Glossary of Chemical Terms

GLOSSARY
absolute zero The coldest temperature possible. Absolute zero (0 K or - 273 °C or - 459 °F) is the temperature at which molecular motion stops. Lower temperatures do not exist. acid A molecular compound that dissolves in solution to form H+ ions. Acids have the ability to dissolve some metals and will turn litmus paper red. acid rain Acidic precipitation in the form of rain; created when fossil fuels are burned, which releases SO2 and NO2 , which then react with water in the atmosphere to form sulfuric acid and nitric acid. acid–base reaction A reaction that forms water and typically a salt. acidic solution A solution containing a concentration of H3 O+ ions greater than 1.0 * 10-7 M (pH 6 7). activation energy The amount of energy that must be absorbed by reactants before a reaction can occur; an energy hump that normally exists between the reactants and products. activity series of metals A listing of metals (and hydrogen) in order of decreasing activity, decreasing ability to oxidize, and decreasing tendency to lose electrons. actual yield The amount of product actually produced by a chemical reaction. addition polymer A polymer formed by addition of monomers to one another without elimination of any atoms. alcohol An organic compound containing an ¬ OH functional group bonded to a carbon atom and having the general formula ROH. aldehyde An organic compound with the general formula RCHO. alkali metals The Group 1A elements, which are highly reactive metals. alkaline battery A dry cell employing half-reactions that use a base. alkaline earth metals The Group 2A elements, which are fairly reactive metals. alkaloids Organic compounds that are typically found in plants and act as bases. alkanes Hydrocarbons in which all carbon atoms are connected by single bonds. Noncyclic alkanes have the general formula CnH2n + 2. alkene A hydrocarbon that contains at least one double bond between carbon atoms. Noncyclic alkenes have the general formula CnH2n. alkyl group In an organic molecule, any group containing only singly bonded carbon atoms and hydrogen atoms. alkyne A hydrocarbon that contains at least one triple bond between carbon atoms. Noncyclic alkynes have the general formula CnH2n - 2. alpha particle A particle consisting of two protons and two 4 neutrons (a helium nucleus), represented by the symbol 2 He. alpha (A) radiation Radiation emitted by an unstable nucleus, consisting of alpha particles. alpha (A)-helix The most common secondary protein structure. The amino acid chain is wrapped into a tight coil from which the side chains extend outward. The structure is maintained by hydrogen bonding interactions between NH and CO groups along the peptide backbone of the protein. amine An organic compound that contains nitrogen and has the general formula NR3 , where R may be an alkyl group or a hydrogen atom. amino acid A molecule containing an amine group, a carboxylic acid group, and an R group (also called a side chain). Amino acids are the building blocks of proteins. amorphous A type of solid matter in which atoms or molecules do not have long-range order (e.g., glass and plastic). amphoteric In Brønsted–Lowry terminology, able to act as either an acid or a base. anion A negatively charged ion. anode The electrode where oxidation occurs in an electrochemical cell. aqueous solution A homogeneous mixture of a substance with water. aromatic ring A ring of carbon atoms containing alternating single and double bonds; another name for the benzene ring. Arrhenius acid A substance that produces H+ ions in aqueous solution. Arrhenius base A substance that produces OH- ions in aqueous solution. atmosphere (atm) The average pressure at sea level, 101,325 Pa (760 mmHg). atom The smallest identifiable unit of an element. atomic element An element that exists in nature with single atoms as the basic unit. atomic mass A weighted average of the masses of each naturally occurring isotope of an element; atomic mass is the average mass of the atoms of an element. atomic mass unit (amu) The unit commonly used to express the masses of protons, neutrons, and nuclei. 1 amu = 1.66 * 10-24 g. atomic number (Z) The number of protons in the nucleus of an atom. atomic size The size of atom, which is determined by how far the outermost electrons are from the nucleus. atomic solid A solid whose component units are individual atoms (e.g., diamond, C; iron, Fe). atomic theory A theory stating that all matter is composed of tiny particles called atoms. Avogadro’s law A law stating that the volume (V) of a gas and the amount of the gas in moles (n) are directly proportional. Avogadro’s number The number of entities in a mole, 6.022 * 1023.

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balanced equation A chemical equation in which the numbers of each type of atom on both sides of the equation are equal. base A molecular compound that dissolves in solution to form OH- ions. Bases have a slippery feel and turn litmus paper blue. base chain The longest continuous chain of carbon atoms in an organic compound. basic solution A solution containing a concentration of OHions greater than 1.0 * 10-7 M (pH 7 7). bent The molecular geometry in which 3 atoms are not in a straight line. This geometry occurs when the central atoms contain 4 electron groups (2 bonding and 2 nonbonding) or 3 electron groups (2 bonding and 1 nonbonding). benzene (C6 H6 ) A particularly stable organic compound consisting of six carbon atoms joined by alternating single and double bonds in a ring structure. beta particle A form of radiation consisting of an energetic electron and represented by the symbol -0 1 e. beta ( B ) radiation Energetic electrons emitted by an unstable nucleus. beta ( B )-pleated sheet A common pattern in the secondary structure of proteins. The protein chain is extended in a zigzag pattern, and the peptide backbones of adjacent strands interact with one another through hydrogen bonding to form sheets. binary acid An acid containing only hydrogen and a nonmetal. binary compound A compound containing only two different kinds of elements. biochemistry The study of the chemical substances and processes that occur in living organisms. Bohr model A model for the atom in which electrons travel around the nucleus in circular orbits at specific, fixed distances from the nucleus. boiling point The temperature at which the vapor pressure of a liquid is equal to the pressure above it. boiling point elevation The increase in the boiling point of a solution caused by the presence of the solute. bonding pair Electrons that are shared between two atoms in a chemical bond. bonding theory A model that predicts how atoms bond together to form molecules. Boyle’s law A law maintaining that the volume (V) of a gas and its pressure (P) are inversely proportional. branched alkane An alkane composed of carbon atoms bonded in chains containing branches. Brønsted–Lowry acid A proton (H+ ion) donor. Brønsted–Lowry base A proton (H+ ion) acceptor. buffer A solution that resists pH change by neutralizing added acid or added base. Calorie (Cal) An energy unit equivalent to 1000 little-c calories. calorie (cal) The amount of energy required to raise the temperature of 1 g of water by 1 °C. carbohydrates Polyhydroxyl aldehydes or ketones or their derivatives, containing multiple ¬ OH groups and often having the general formula (CH2 O)n. carbonyl group A carbon atom double bonded to an oxygen atom.

carboxylic acid An organic compound with the general formula RCOOH. catalyst A substance that increases the rate of a chemical reaction but is not consumed by the reaction. cathode The electrode where reduction occurs in an electrochemical cell. cation A positively charged ion. cell The smallest structural unit of living organisms that has the properties associated with life. cell membrane The structure that bounds the cell and holds the contents of the cell together. cellulose A common polysaccharide composed of repeating glucose units linked together. Celsius (°C) scale A temperature scale often used by scientists. On this scale, water freezes at 0 °C and boils at 100 °C at 1 atm pressure. Room temperature is approximately 22 °C. chain reaction A self-sustaining chemical or nuclear reaction yielding energy or products that cause further reactions of the same kind. charge A fundamental property of protons and electrons. Charged particles experience forces such that like charges repel and unlike charges attract. Charles’s law A law stating that the volume (V) of a gas and its temperature (T) expressed in kelvins are directly proportional. chemical bond The sharing or transfer of electrons to attain stable electron configurations among the bonding atoms. chemical change A change in which matter changes its composition. chemical energy The energy associated with chemical changes. chemical equation An equation that represents a chemical reaction; the reactants are on the left side of the equation and the products are on the right side. chemical formula A way to represent a compound. At a minimum, the chemical formula indicates the elements present in the compound and the relative number of atoms of each element. chemical properties Properties that a substance can display only through changing its composition. chemical reaction The process by which one or more substances transform into different substances via a chemical change. Chemical reactions often emit or absorb energy. chemical symbol A one- or two-letter abbreviation for an element. Chemical symbols are listed directly below the atomic number in the periodic table. chemistry The science that seeks to understand the behavior of matter by studying what atoms and molecules do. chromosome A biological structure containing genes, located within the nucleus of a cell. codon A sequence of three bases in a nucleic acid that codes for one amino acid. colligative properties Physical properties of solutions that depend on the number of solute particles present but not the type of solute particles. collision theory A theory of reaction rates stating that effective collisions between reactant molecules must take place in order for the reaction to occur.

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color change One type of evidence of a chemical reaction, involving the change in color of a substance after a reaction. combined gas law A law that combines Boyle’s law and Charles’s law; it is used to calculate how a property of a gas (P, V, or T) changes when two other properties are changed at the same time. combustion reaction A reaction in which a substance reacts with oxygen, emitting heat and forming one or more oxygencontaining compounds. complementary base In DNA, a base capable of precise pairing with a specific other DNA base. complete ionic equation A chemical equation showing all the species as they are actually present in solution. complex carbohydrate A carbohydrate composed of many repeating saccharide units. compound A substance composed of two or more elements in fixed, definite proportions. compressible Able to occupy a smaller volume when subjected to increased pressure. Gases are compressible because, in the gas phase, atoms or molecules are widely separated. concentrated solution A solution containing large amounts of solute. condensation A physical change in which a substance is converted from its gaseous form to its liquid form. condensation polymer A class of polymers that expel atoms, usually water, during their formation or polymerization. condensed structural formula A shorthand way of writing a structural formula. conjugate acid–base pair In Brønsted–Lowry terminology, two substances related to each other by the transfer of a proton. conservation of energy, law of A law stating that energy can be neither created nor destroyed. The total amount of energy is constant and cannot change; it can only be transferred from one object to another or converted from one form to another. conservation of mass, law of A law stating that in a chemical reaction, matter is neither created nor destroyed. constant composition, law of A law stating that all samples of a given compound have the same proportions of their constituent elements. conversion factor A factor used to convert between two separate units; a conversion factor is constructed from any two quantities known to be equivalent. copolymers Polymers that are composed of two different kinds of monomers and result in chains composed of alternating units rather than a single repeating unit. core electrons The electrons that are not in the outermost principal shell of an atom. corrosion The oxidation of metals (e.g., rusting of iron). covalent atomic solid An atomic solid, such as diamond, that is held together by covalent bonds. covalent bond The bond that results when two nonmetals combine in a chemical reaction. In a covalent bond, the atoms share their electrons. critical mass The mass of uranium or plutonium required for a nuclear reaction to be self-sustaining. crystalline A type of solid matter with atoms or molecules arranged in a well-ordered, three-dimensional array with long-range, repeating order (e.g., salt and diamond).

cytoplasm In a cell, the region between the nucleus and the cell membrane. Dalton’s law of partial pressure A law stating that the sum of the partial pressures of each component in a gas mixture equals the total pressure. daughter nuclide The nuclide product of a nuclear decay. decimal part One part of a number expressed in scientific notation. decomposition A reaction in which a complex substance decomposes to form simpler substances; AB ¡ A + B. density (d) A fundamental property of materials that relates mass and volume and differs from one substance to another. The units of density are those of mass divided by volume, most commonly expressed in g> cm3, g> mL, or g> L. derived unit A unit formed from the combination of other units. dilute solution A solution containing small amounts of solute. dimer A molecule formed by the joining together of two smaller molecules. dipeptide Two amino acids linked together via a peptide bond. dipole moment A measure of the separation of charge in a bond or in a molecule. diprotic acid An acid containing two ionizable protons. disaccharide A carbohydrate that can be decomposed into two simpler carbohydrates. dispersion force The intermolecular force present in all molecules and atoms. Dispersion forces are caused by fluctuations in the electron distribution within molecules or atoms. displacement A reaction in which one element displaces another in a compound; A + BC ¡ AC + B. dissociation In aqueous solution, the process by which a solid ionic compound separates into its ions. disubstituted benzene A benzene in which two hydrogen atoms have been replaced by an atom or group of atoms. DNA (deoxyribonucleic acid) Long chainlike molecules that occur in the nucleus of cells and act as blueprints for the construction of proteins. dot structure A drawing that represents the valence electrons in atoms as dots; it shows a chemical bond as the sharing or transfer of electron dots. double bond The bond that exists when two electron pairs are shared between two atoms. In general, double bonds are shorter and stronger than single bonds. double displacement A reaction in which two elements or groups of elements in two different compounds exchange places to form two new compounds; AB + CD ¡ AD + CB. dry cell An ordinary battery (voltaic cell); it does not contain large amounts of liquid water. duet The name for the two electrons corresponding to a stable Lewis structure in hydrogen and helium. dynamic equilibrium In a chemical reaction, the condition in which the rate of the forward reaction equals the rate of the reverse reaction. electrical current The flow of electric charge—for example, electrons flowing through a wire or ions through a solution.

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electrical energy Energy associated with the flow of electric charge. electrochemical cell A device that creates electrical current from a redox reaction. electrolysis A process in which electrical current is used to drive an otherwise nonspontaneous redox reaction. electrolytic cell An electrochemical cell used for electrolysis. electromagnetic radiation A type of energy that travels through space at a constant speed of 3.0 * 108 m> s (186,000 miles/s) and exhibits both wavelike and particlelike behavior. Light is a form of electromagnetic radiation. electromagnetic spectrum A spectrum that includes all wavelengths of electromagnetic radiation. electron A negatively charged particle that occupies most of the atom’s volume but contributes almost none of its mass. electron configuration A representation that shows the occupation of orbitals by electrons for a particular element. electron geometry The geometrical arrangement of the electron groups in a molecule. electron group A general term for a lone pair, single bond, or multiple bond in a molecule. electron spin A fundamental property of all electrons that causes them to have magnetic fields associated with them. The 1 spin of an electron can either be oriented up A + 1 2 B or down A - 2 B . electronegativity The ability of an element to attract electrons within a covalent bond. element A substance that cannot be broken down into simpler substances. emission spectrum A spectrum associated with the emission of electromagnetic radiation by elements or compounds. empirical formula A formula for a compound that gives the smallest whole-number ratio of each type of atom. empirical formula molar mass The sum of the molar masses of all the atoms in an empirical formula. endothermic Describes a process that absorbs heat energy. endothermic reaction A chemical reaction that absorbs energy from the surroundings. energy The capacity to do work. English system A unit system commonly used in the United States. enzymes Biological catalysts that increase the rates of biochemical reactions; enzymes are abundant in living organisms. equilibrium constant (Keq) The ratio, at equilibrium, of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients. equivalence point The point in a reaction at which the reactants are in exact stoichiometric proportions. equivalent The stoichiometric proportions of elements and compounds in a chemical equation. ester An organic compound with the general formula RCOOR. ester linkage A type of bond with the general structure ¬ COO ¬ . Ester linkages join glycerol to fatty acids. ether An organic compound with the general formula ROR. evaporation A process in which molecules of a liquid, undergoing constant random motion, acquire enough energy to overcome attractions to neighbors and enter the gas phase.

excited state An unstable state for an atom or a molecule in which energy has been absorbed but not reemitted, raising an electron from the ground state into a higher energy orbital. exothermic Describes a process that releases heat energy. exothermic reaction A chemical reaction that releases energy to the surroundings. experiment A procedure that attempts to measure observable predictions to test a theory or law. exponent A number that represents the number of times a term is multiplied by itself. For example, in 24 the exponent is 4 and represents 2 * 2 * 2 * 2. exponential part One part of a number expressed in scientific notation; it represents the number of places the decimal point has moved. Fahrenheit (°F) scale The temperature scale that is most familiar in the United States; water freezes at 32 °F and boils at 212 °F at 1 atm prssure. family (of elements) A group of elements that have similar outer electron configurations and therefore similar properties. Families occur in vertical columns in the periodic table. family (of organic compounds) A group of organic compounds with the same functional group. fatty acid A type of lipid consisting of a carboxylic acid with a long hydrocarbon tail. film badge dosimeter Badges used to measure radiation exposure, consisting of photographic film held in a small case that is pinned to clothing. fission, nuclear The process by which a heavy nucleus is split into nuclei of smaller masses and energy is emitted. formula mass The average mass of the molecules (or formula units) that compose a compound. formula unit The basic unit of ionic compounds; the smallest electrically neutral collection of cations and anions that compose the compound. freezing point depression The decrease in the freezing point of a solvent caused by the presence of a solute. frequency The number of wave cycles or crests that pass through a stationary point in one second. fuel cell A voltaic cell in which the reactants are constantly replenished. functional group A set of atoms that characterize a family of organic compounds. fusion, nuclear The combination of light atomic nuclei to form heavier ones with emission of large amounts of energy. galvanic (voltaic) cell An electrochemical cell that spontaneously produces electrical current. gamma radiation High-energy, short-wavelength electromagnetic radiation emitted by an atomic nucleus. gamma rays The shortest-wavelength, most energetic form of electromagnetic radiation. Gamma ray photons are represented 0 by the symbol 0 g. gas A state of matter in which atoms or molecules are widely separated and free to move relative to one another. gas-evolution reaction A reaction that occurs in solution and forms a gas as one of the products. gas formation One type of evidence of a chemical reaction, a gas forms when two substances are mixed together.

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Geiger-Müller counter A radioactivity detector consisting of a chamber filled with argon gas that discharges electrical signals when high-energy particles pass through it. gene A sequence of codons within a DNA molecule that codes for a single protein. Genes vary in length from hundreds to thousands of codons. genetic material The inheritable blueprint for making organisms. glycogen A type of polysaccharide; it has a structure similar to that of starch, but the chain is highly branched. glycolipid A biological molecule composed of a nonpolar fatty acid and hydrocarbon chain and a polar section composed of a sugar molecule such as glucose. glycoside linkage The link between monosaccharides in a polysaccharide. ground state The state of an atom or molecule in which the electrons occupy the lowest possible energy orbitals available. group (of elements) Elements that have similar outer electron configurations and therefore similar properties. Groups occur in vertical columns in the periodic table. half-cell A compartment in which the oxidation or reduction half-reaction occurs in a galvanic or voltaic cell. half-life The time it takes for one-half of the parent nuclides in a radioactive sample to decay to the daughter nuclides. half-reaction Either the oxidation part or the reduction part of a redox reaction. halogens The Group 7A elements, which are very reactive nonmetals. heat absorption One type of evidence of a chemical reaction, involving the intake of energy. heat capacity The quantity of heat energy required to change the temperature of a given amount of a substance by 1 °C. heat emission One type of evidence of a chemical reaction, involving the evolution of thermal energy. heat of fusion The amount of heat required to melt one mole of a solid at its melting point with no change in temperature. heat of vaporization The amount of heat required to vaporize one mole of a liquid at its boiling point with no change in temperature. heterogeneous mixture A mixture, such as oil and water, that has two or more regions with different compositions. homogeneous mixture A mixture, such as salt water, that has the same composition throughout. human genome All of the genetic material of a human being; the total DNA of a human cell. Hund’s rule A rule stating that when filling orbitals of equal energy, electrons will occupy empty orbitals singly before pairing with other electrons. hydrocarbon A compound that contains only carbon and hydrogen atoms. hydrogen bond A strong dipole–dipole interaction between molecules containing hydrogen directly bonded to a small, highly electronegative atom, such as N, O, or F. hydrogenation The chemical addition of hydrogen to a compound. hydronium ion The H3 O+ ion. Chemists often use H+(aq) and H3 O+(aq) interchangeably to mean the same thing—a hydronium ion.

hypothesis A theory or law before it has become well established; a tentative explanation for an observation or a scientific problem that can be tested by further investigation. hypoxia A shortage of oxygen in the tissues of the body. ideal gas law A law that combines the four properties of a gas—pressure (P), volume (V), temperature (T), and number of moles (n) in a single equation showing their interrelatedness: PV = nRT (R = ideal gas constant). indicator A substance that changes color with acidity level, often used to detect the endpoint of a titration. infrared (IR) light The fraction of the electromagnetic spectrum between visible light and microwaves. Infrared light is invisible to the human eye. insoluble Not soluble in water. instantaneous dipole A type of intermolecular force resulting from transient shifts in electron density within an atom or molecule. intermolecular forces Attractive forces that exist between molecules. International System (SI) The standard set of units for science measurements, based on the metric system. ion An atom (or group of atoms) that has gained or lost one or more electrons, so that it has an electric charge. ion product constant (Kw) The product of the H3 O+ ion concentration and the OH- ion concentration in an aqueous solution. At room temperature, Kw = 1.0 * 10-14. ionic bond The bond that results when a metal and a nonmetal combine in a chemical reaction. In an ionic bond, the metal transfers one or more electrons to the nonmetal. ionic compound A compound formed between a metal and one or more nonmetals. ionic solid A solid compound composed of metals and nonmetals joined by ionic bonds. ionization The forming of ions. ionization energy The energy required to remove an electron from an atom in the gaseous state. ionizing power The ability of radiation to ionize other molecules and atoms. isomers Molecules with the same molecular formula but different structures. isoosmotic Describes solutions having equal osmotic pressure. isotope scanning The use of radioactive isotopes to identify disease in the body. isotopes Atoms with the same number of protons but different numbers of neutrons. Kelvin (K) scale The temperature scale that assigns 0 K to the coldest temperature possible, absolute zero ( - 273 °C or - 459 °F), the temperature at which molecular motion stops. The size of the kelvin is identical to that of the Celsius degree. ketone An organic compound with the general formula RCOR. kilogram (kg) The SI standard unit of mass. kilowatt-hour (kWh) A unit of energy equal to 3.6 million joules. kinetic energy Energy associated with the motion of an object. kinetic molecular theory A simple model for gases that predicts the behavior of most gases under many conditions. Le Châtelier’s principle A principle stating that when a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance.

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lead-acid storage battery An automobile battery consisting of six electrochemical cells wired in series. Each cell produces 2 volts for a total of 12 volts. Lewis structure A drawing that represents chemical bonds between atoms as shared or transferred electrons; the valence electrons of atoms are represented as dots. Lewis theory A simple theory for chemical bonding involving diagrams showing bonds between atoms as lines or dots. In this theory, atoms bond together to obtain stable octets (8 valence electrons). light emission One type of evidence of a chemical reaction, involving the giving off of electromagnetic radiation. limiting reactant The reactant that determines the amount of product formed in a chemical reaction. linear Describes the molecular geometry of a molecule containing two electron groups (two bonding groups and no lone pairs). linearly related A relationship between two variables such that, when they are plotted one against the other, the graph produced is a straight line. lipid A cellular component that is insoluble in water but soluble in nonpolar solvents. lipid bilayer A structure formed by lipids in the cell membrane. liquid A state of matter in which atoms or molecules are packed close to each other (about as closely as in a solid) but are free to move around and by each other. logarithmic scale A scale involving logarithms. A logarithm entails an exponent that indicates the power to which a number is raised to produce a given number (e.g., the logarithm of 100 to the base 10 is 2). lone pair Electrons that are only on one atom in a Lewis structure. main-group elements Groups 1A–8A on the periodic table. These groups have properties that tend to be predictable based on their position in the periodic table. mass A measure of the quantity of matter within an object. mass number (A) The sum of the number of neutrons and protons in an atom. mass percent composition (or mass percent) The percentage, by mass, of each element in a compound. matter Anything that occupies space and has mass. Matter exists in three different states: solid, liquid, and gas. melting point The temperature at which a solid turns into a liquid. messenger RNA (mRNA) Long chainlike molecules that act as blueprints for the construction of proteins. metallic atomic solid An atomic solid, such as iron, which is held together by metallic bonds that, in the simplest model, consist of positively charged ions in a sea of electrons. metallic character The properties typical of a metal, especially the tendency to lose electrons in chemical reactions. Elements become more metallic as you move from right to left across the periodic table. metalloids Those elements that fall along the boundary between the metals and the nonmetals in the periodic table; their properties are intermediate between those of metals and those of nonmetals.

metals Elements that tend to lose electrons in chemical reactions. They are found at the left side and in the center of the periodic table. meter (m) The SI standard unit of length. metric system The unit system commonly used throughout most of the world. microwaves The part of the electromagnetic spectrum between the infrared region and the radio wave region. Microwaves are efficiently absorbed by water molecules and can therefore be used to heat water-containing substances. millimeter of mercury (mmHg) A unit of pressure that originates from the method used to measure pressure with a barometer. Also called a torr. miscibility The ability of two liquids to mix without separating into two phases, or the ability of one liquid to mix with (dissolve in) another liquid. mixture A substance composed of two or more different types of atoms or molecules combined in variable proportions. molality (m) A common unit of solution concentration, defined as the number of moles of solute per kilogram of solvent. molar mass The mass of one mole of atoms of an element or one mole of molecules (or formula units) for a compound. An element’s molar mass in grams per mole is numerically equivalent to the element’s atomic mass in amu. molar solubility The solubility of a substance in units of moles per liter (mol> L). molar volume The volume occupied by one mole of gas. Under standard temperature and pressure conditions the molar volume of ideal gas is 22.5 L. molarity (M) A common unit of solution concentration, defined as the number of moles of solute per liter of solution. mole Avogadro’s number (6.022 * 1023) of particles— especially, of atoms, ions, or molecules. A mole of any element has a mass in grams that is numerically equivalent to its atomic mass in amu. molecular compound A compound formed from two or more nonmetals. Molecular compounds have distinct molecules as their simplest identifiable units. molecular element An element that does not normally exist in nature with single atoms as the basic unit. These elements usually exist as diatomic molecules—2 atoms of that element bonded together—as their basic units. molecular equation A chemical equation showing the complete, neutral formulas for every compound in a reaction. molecular formula A formula for a compound that gives the specific number of each type of atom in a molecule. molecular geometry The geometrical arrangement of the atoms in a molecule. molecular solid A solid whose composite units are molecules. molecule Two or more atoms joined in a specific arrangement by chemical bonds. A molecule is the smallest identifiable unit of a molecular compound. monomer An individual repeating unit that makes up a polymer. monoprotic acid An acid containing only one ionizable proton. monosaccharide A carbohydrate that cannot be decomposed into simpler carbohydrates.

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monosubstituted benzene A benzene in which one of the hydrogen atoms has been replaced by another atom or group of atoms. net ionic equation An equation that shows only the species that actually participate in a reaction. neutral solution A solution in which the concentrations of H3 O+ and OH- are equal (pH = 7). neutralization A reaction that takes place when an acid and a base are mixed; the H+(aq) from the acid combines with the OH-(aq) from the base to form H2 O(l). neutron A nuclear particle with no electrical charge and nearly the same mass as a proton. nitrogen narcosis An increase in nitrogen concentration in bodily tissues and fluids that results in feelings of drunkenness. noble gases The Group 8A elements, which are chemically unreactive. nonbonding atomic solid An atomic solid that is held together by relatively weak dispersion forces. nonelectrolyte solution A solution containing a solute that dissolves as molecules; therefore, the solution does not conduct electricity. nonmetals Elements that tend to gain electrons in chemical reactions. They are found at the upper right side of the periodic table. nonpolar molecule A molecule that does not have a net dipole moment. nonvolatile Describes a compound that does not vaporize easily. normal alkane (or n-alkane) An alkane composed of carbon atoms bonded in a straight chain with no branches. normal boiling point The boiling point of a liquid at a pressure of 1 atmosphere. nuclear equation An equation that represents the changes that occur during radioactivity and other nuclear processes. nuclear radiation The energetic particles emitted from the nucleus of an atom when it is undergoing a nuclear process. nuclear theory of the atom A theory stating that most of the atom’s mass and all of its positive charge is contained in a small, dense nucleus. Most of the volume of the atom is empty space occupied by negatively charged electrons. nucleic acids Biological molecules, such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), that store and transmit genetic information. nucleotide An individual unit of a nucleic acid. Nucleic acids are polymers of nucleotides. nucleus (of a cell) The part of the cell that contains the genetic material. nucleus (of an atom) The small core containing most of the atom’s mass and all of its positive charge. The nucleus is made up of protons and neutrons. observation Often the first step in the scientific method. An observation must measure or describe something about the physical world. octet The number of electrons, eight, around atoms with stable Lewis structures. octet rule A rule that states that an atom will give up, accept, or share electrons in order to achieve a filled outer electron shell, which usually consists of 8 electrons.

orbital The region around the nucleus of an atom where an electron is most likely to be found. orbital diagram An electron configuration in which electrons are represented as arrows in boxes corresponding to orbitals of a particular atom. organic chemistry The study of carbon-containing compounds and their reactions. organic molecule A molecule whose main structural component is carbon. osmosis The flow of solvent from a lower-concentration solution through a semipermeable membrane to a higherconcentration solution. osmotic pressure The pressure produced on the surface of a semipermeable membrane by osmosis or the pressure required to stop osmotic flow. oxidation The gain of oxygen, the loss of hydrogen, or the loss of electrons (the most fundamental definition). oxidation state (or oxidation number) A number that can be used as an aid in writing formulas and balancing equations. It is computed for each element based on the number of electrons assigned to it in a scheme where the most electronegative element is assigned all of the bonding electrons. oxidation–reduction (redox) reaction A reaction in which electrons are transferred from one substance to another. oxidizing agent In a redox reaction, the substance being reduced. Oxidizing agents tend to gain electrons easily. oxyacid An acid containing hydrogen, a nonmetal, and oxygen. oxyanion An anion containing oxygen. Most polyatomic ions are oxyanions. oxygen toxicity The result of increased oxygen concentration in bodily tissues. parent nuclide The original nuclide in a nuclear decay. partial pressure The pressure due to any individual component in a gas mixture. pascal (Pa) The SI unit of pressure, defined as 1 newton per square meter. Pauli exclusion principle A principle stating that no more than two electrons can occupy an orbital and that the two electrons must have opposite spins. penetrating power The ability of a radioactive particle to penetrate matter. peptide bond The bond between the amine end of one amino acid and the carboxylic acid end of another. Amino acids link together via peptide bonds to form proteins. percent natural abundance The percentage amount of each isotope of an element in a naturally occurring sample of the element. percent yield In a chemical reaction, the percentage of the theoretical yield that was actually attained. period A horizontal row of the periodic table. periodic law A law that states that when the elements are arranged in order of increasing relative mass, certain sets of properties recur periodically. periodic table An arrangement of the elements in which atomic number increases from left to right and elements with similar properties fall in columns called families or groups.

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permanent dipole A separation of charge resulting from the unequal sharing of electrons between atoms. pH scale A scale used to quantify acidity or basicity. A pH of 7 is neutral; a pH lower than 7 is acidic, and a pH greater than 7 is basic. The pH is defined as follows: pH = - log3H3 O+4. phenyl group The term for a benzene ring when other substituents are attached to it. phospholipid A lipid with the same basic structure as a triglyceride, except that one of the fatty acid groups is replaced with a phosphate group. phosphorescence The slow, long-lived emission of light that sometimes follows the absorption of light by some atoms and molecules. photon A particle of light or a packet of light energy. physical change A change in which matter does not change its composition, even though its appearance might change. physical properties Those properties that a substance displays without changing its composition. polar covalent bond A covalent bond between atoms of different electronegativities. Polar covalent bonds have a dipole moment. polar molecule A molecule with polar bonds that add together to create a net dipole moment. polyatomic ion An ion composed of a group of atoms with an overall charge. polymer A molecule with many similar units, called monomers, bonded together in a long chain. polypeptide A short chain of amino acids joined by peptide bonds. polysaccharide A long, chainlike molecule composed of many linked monosaccharide units. Polysaccharides are polymers of monosaccharides. positron A nuclear particle that has the mass of an electron but carries a + 1 charge. positron emission Expulsion of a positron from an unstable atomic nucleus. In positron emission, a proton is transformed into a neutron. potential energy The energy of a body that is associated with its position or the arrangement of its parts. precipitate An insoluble product formed through the reaction of two solutions containing soluble compounds. precipitation reaction A reaction that forms a solid or precipitate when two aqueous solutions are mixed. prefix multipliers Prefixes used by the SI system with the standard units. These multipliers change the value of the unit by powers of 10. pressure The force exerted per unit area by gaseous molecules as they collide with the surfaces around them. primary protein structure The sequence of amino acids in a protein’s chain. Primary protein structure is maintained by the covalent peptide bonds between individual amino acids. principal quantum number A number that indicates the shell that an electron occupies. principal shell The shell indicated by the principal quantum number. products The final substances produced in a chemical reaction; represented on the right side of a chemical equation. properties The characteristics we use to distinguish one substance from another.

protein A biological molecule composed of a long chain of amino acids joined by peptide bonds. In living organisms, proteins serve many varied and important functions. proton A positively charged nuclear particle. A proton’s mass is approximately 1 amu. pure substance A substance composed of only one type of atom or molecule. quantification The assigning of a number to an observation so as to specify a quantity or property precisely. quantum ( pl. quanta) The precise amount of energy possessed by a photon; the difference in energy between two atomic orbitals. quantum number (n) An integer that specifies the energy of an orbital. The higher the quantum number n, the greater the distance between the electron and the nucleus and the higher its energy. quantum-mechanical model The foundation of modern chemistry; explains how electrons exist in atoms, and how they affect the chemical and physical properties of elements. quaternary structure In a protein, the way that individual chains fit together to compose the protein. Quaternary structure is maintained by interactions between the R groups of amino acids on the different chains. R group (side chain) An organic group attached to the central carbon atom of an amino acid. radio waves The longest wavelength and least energetic form of electromagnetic radiation. radioactive Describes a substance that emits tiny, invisible, energetic particles from the nuclei of its component atoms. radioactivity The emission of tiny, invisible, energetic particles from the unstable nuclei of atoms. Many of these particles can penetrate matter. radiocarbon dating A technique used to estimate the age of fossils and artifacts through the measurement of natural radioactivity of carbon atoms in the environment. radiotherapy Treatment of disease with radiation, such as the use of gamma rays to kill rapidly dividing cancer cells. random coil The name given to an irregular pattern of a secondary protein structure. rate of a chemical reaction (reaction rate) The amount of reactant that changes to product in a given period of time. Also defined as the amount of a product that forms in a given period of time. reactants The initial substances in a chemical reaction, represented on the left side of a chemical equation. recrystallization A technique used to purify a solid; involves dissolving the solid in a solvent at high temperature, creating a saturated solution, then cooling the solution to cause the crystallization of the solid. reducing agent In a redox reaction, the substance being oxidized. Reducing agents tend to lose electrons easily. reduction The loss of oxygen, the gain of hydrogen, or the gain of electrons (the most fundamental definition). rem Stands for roentgen equivalent man; a weighted measure of radiation exposure that accounts for the ionizing power of the different types of radiation. resonance structures Two or more Lewis structures that are necessary to describe the bonding in a molecule or ion. reversible reaction A reaction that is able to proceed in both the forward and reverse directions.

GLOSSARY |

G-9

RNA (ribonucleic acid) Long chainlike molecules that occur throughout cells and take part in the construction of proteins. salt An ionic compound that usually remains dissolved in a solution after an acid–base reaction has occurred. salt bridge An inverted, U-shaped tube containing a strong electrolyte; completes the circuit in an electrochemical cell by allowing the flow of ions between the two half-cells. saturated fat A triglyceride composed of saturated fatty acids. Saturated fat tends to be solid at room temperature. saturated hydrocarbon A hydrocarbon that contains no double or triple bonds between the carbon atoms. saturated solution A solution that holds the maximum amount of solute under the solution conditions. If additional solute is added to a saturated solution, it will not dissolve. scientific law A statement that summarizes past observations and predicts future ones. Scientific laws are usually formulated from a series of related observations. scientific method The way that scientists learn about the natural world. The scientific method involves observations, laws, hypotheses, theories, and experimentation. scientific notation A system used to write very big or very small numbers, often containing many zeros, more compactly and precisely. A number written in scientific notation consists of a decimal part and an exponential part (10 raised to a particular exponent). scintillation counter A device used to detect radioactivity in which energetic particles traverse a material that emits ultraviolet or visible light when excited by their passage. The light is detected and turned into an electrical signal. second (s) The SI standard unit of time. secondary protein structure Short-range periodic or repeating patterns often found in proteins. Secondary protein structure is maintained by interactions between amino acids that are fairly close together in the linear sequence of the protein chain or adjacent to each other on neighboring chains. semiconductor A compound or element exhibiting intermediate electrical conductivity that can be changed and controlled. semipermeable membrane A membrane that selectively allows some substances to pass through but not others. SI units The most convenient system of units for science measurements, based on the metric system. The set of standard units agreed on by scientists throughout the world. significant digits (figures) The non-place-holding digits in a reported measurement; they represent the precision of a measured quantity. simple carbohydrate (simple sugar) A monosaccharide or disaccharide. single bond A chemical bond in which one electron pair is shared between two atoms. solid A state of matter in which atoms or molecules are packed close to each other in fixed locations. solid formation One type of evidence of a chemical reaction, involving the formation of a solid. solubility The amount of a compound, usually in grams, that will dissolve in a certain amount of solvent. solubility rules A set of empirical rules used to determine whether an ionic compound is soluble. solubility-product constant (Ksp) The equilibrium expression for a chemical equation that represents the dissolving of an ionic compound in solution.

soluble Dissolves in solution. solute The minority component of a solution. solution A homogeneous mixture of two or more substances. solvent The majority component of a solution. specific heat capacity (or specific heat) The heat capacity of a substance in joules per gram degree celsius (J> g °C). spectator ions Ions that do not participate in a reaction; they appear unchanged on both sides of a chemical equation. standard temperature and pressure (STP) Conditions often assumed in calculations involving gases: T = 0 °C (273 K) and P = 1 atm. starch A common polysaccharide composed of repeating glucose units. states of matter The three forms in which matter can exist: solid, liquid, and gas. steroid A biological compound containing a 17-carbon 4-ring system. stock solution A concentrated form in which solutions are often stored. stoichiometry The numerical relationships among chemical quantities in a balanced chemical equation. Stoichiometry allows us to predict the amounts of products that form in a chemical reaction based on the amounts of reactants. strong acid An acid that completely ionizes in solution. strong base A base that completely dissociates in solution. strong electrolyte A substance whose aqueous solutions are good conductors of electricity. strong electrolyte solution A solution containing a solute that dissociates into ions; therefore, a solution that conducts electricity well. structural formula A two-dimensional representation of molecules that not only shows the number and type of atoms, but also how the atoms are bonded together. sublimation A physical change in which a substance is converted from its solid form directly into its gaseous form. subshell In quantum mechanics, specifies the shape of the orbital and is represented by different letters (s, p, d, f ). substituent An atom or a group of atoms that has been substituted for a hydrogen atom in an organic compound. substitution reaction A reaction in which one or more atoms are replaced by one or more different atoms. supersaturated solution A solution holding more than the normal maximum amount of solute. surface tension The tendency of liquids to minimize their surface area, resulting in a “skin” on the surface of the liquid. synthesis A reaction in which simpler substances combine to form more complex substances; A + B ¡ AB. temporary dipole A type of intermolecular force resulting from transient shifts in electron density within an atom or molecule. terminal atom An atom that is located at the end of a molecule or chain. tertiary structure A protein’s structure that consists of the large-scale bends and folds due to interactions between the R groups of amino acids that are separated by large distances in the linear sequence of the protein chain. tetrahedral The molecular geometry of a molecule containing four electron groups (four bonding groups and no lone pairs).

G-10

| GLOSSARY

theoretical yield The maximum amount of product that can be made in a chemical reaction based on the amount of limiting reactant. theory A proposed explanation for observations and laws. A theory presents a model of the way nature works and predicts behavior that extends well beyond the observations and laws from which it was formed. titration A laboratory procedure used to determine the amount of a substance in solution. In a titration, a reactant in a solution of known concentration is reacted with another reactant in a solution of unknown concentration until the reaction reaches the endpoint. torr A unit of pressure named after the Italian physicist Evangelista Torricelli; also called a millimeter of mercury. transition metals The elements in the middle of the periodic table whose properties tend to be less predictable based simply on their position in the periodic table. Transition metals lose electrons in their chemical reactions, but do not necessarily acquire noble gas configurations. triglyceride A fat or oil; a tryglyceride is a tri-ester composed of glycerol with three fatty acids attached. trigonal planar The molecular geometry of a molecule containing three electron groups, three bonding groups, and no lone pairs. trigonal pyramidal The molecular geometry of a molecule containing four electron groups, three bonding groups, and one lone pair. triple bond A chemical bond consisting of three electron pairs shared between two atoms. In general, triple bonds are shorter and stronger than double bonds. Type I compounds Compounds containing metals that always form cations with the same charge. Type II compounds Compounds containing metals that can form cations with different charges. ultraviolet (UV) light The fraction of the electromagnetic spectrum between the visible region and the X-ray region. UV light is invisible to the human eye. units Previously agreed-on quantities used to report experimental measurements. Units are vital in chemistry. unsaturated fat (or oil) A triglyceride composed of unsaturated fatty acids. Unsaturated fats tend to be liquids at room temperature.

unsaturated hydrocarbon A hydrocarbon that contains one or more double or triple bonds between its carbon atoms. unsaturated solution A solution holding less than the maximum possible amount of solute under the solution conditions. valence electrons The electrons in the outermost principal shell of an atom; they are involved in chemical bonding. valence shell electron pair repulsion (VSEPR) A theory that allows prediction of the shapes of molecules based on the idea that electrons—either as lone pairs or as bonding pairs—repel one another. vapor pressure The partial pressure of a vapor in dynamic equilibrium with its liquid. vaporization The phase transition between a liquid and a gas. viscosity The resistance of a liquid to flow; manifestation of intermolecular forces. visible light The fraction of the electromagnetic spectrum that is visible to the human eye, bounded by wavelengths of 400 nm (violet) and 780 nm (red). vital force A mystical or supernatural power that, it was once believed, was possessed only by living organisms and allowed them to produce organic compounds. vitalism The belief that living things contain a nonphysical “force” that allows them to synthesize organic compounds. volatile Tending to vaporize easily. voltage The potential difference between two electrodes; the driving force that causes electrons to flow. volume A measure of space. Any unit of length, when cubed, becomes a unit of volume. wavelength The distance between adjacent wave crests in a wave. weak acid An acid that does not completely ionize in solution. weak base solution. A base that does not completely dissociate in

weak electrolyte A substance whose aqueous solutions are poor conductors of electricity. X-rays The portion of the electromagnetic spectrum between the ultraviolet (UV) region and the gamma-ray region.