What is the Atomic Number
Content
What is the Atomic Number? The number of protons in the nucleus is called the atomic number. For sodium (Na) the atomic number is11. The atomic number tells you what the element is (see the periodic table). The atomic number of an element never changes. What is the Mass Number? The number of protons plus the number of neutrons is called the mass number. Sodium has 11 protons and 12 neutrons. The mass number is 11 +12 = 23. The mass number is the total number of particles in the nucleus. The mass number and the atomic number are written above and below the chemical symbol for the element, as shown.
What is an Isotope? Atoms of the same element may have different numbers of neutrons. These are called isotopes. For example, Chlorine (atomic number17) may have 18 or 20 neutrons. The mass number will be either 17 + 18 = 35, or 17+ 20 = 37.
Isotopes of the same element have the same chemical properties because the number of protons and electrons are the same. What are Electron Shells (energy levels)? Electrons in atoms are in shells (shown as circles around the nucleus). The shells can also be called energy levels. We will use the term shell rather than energy level but either is acceptable. The maximum number of electrons in each shell, going from the middle to the outside, is 2, 8, 8, 18. Below is a picture of a potassium atom. Its electron structure is2, 8, 8, 1.
An atom that has the maximum number of electrons in its outer shell will be stable. This means that it will not react with other atoms. It belongs to a group called the noble gases.
The electron shells are said to be full. The inner shells of an atom are always full. If the outer shell of an atom has less than its maximum number of electrons (see potassium above) then it will not be stable. It will react with other atoms to get a full outer shell. Ions also have a full outer shell of electrons but because they have a charge they will react and form ionic bonds with other oppositely charged ions What is the Difference between an Atom and an Ion? An atom has the same number of protons and electrons. An atom has no overall electric charge. If an atom loses or gains electrons it is no longer called an atom. It is called an ion. An ion has a full outer shell of electrons. An ion has an electric charge. Why do Chemical Reactions Happen? All chemical reactions happen because atoms are trying to get a full outer shell of electrons. The total number of atoms is the same before and after the reaction. When an atom reacts with another atom to form a chemical bond
it will either 1. Lose electrons to form a stable positive ion. 2. Gain electrons to form a stable negative ion. Or 3. Share electrons to form a stable molecule What happens when a Sodium Atom becomes a Sodium Ion? A sodium atom has 1 electron in its outer shell. It is in group 1 of the periodic table. When sodium reacts with non-metals (for example chlorine) it will lose its outer electron. Its outer shell will then have no electrons. It is as though the outer shell has vanished. The next shell in is full. This full inner shell becomes the new full outer shell.
The sodium atom loses its outer electron to become a sodium ion. The sodium ion still has 11 protons (11 positive charges) but now only 10 electrons (10 negative charges). The sodium ion has an extra positive charge, shown by
the + sign. All group 1metals will form a 1+ ion when they react with non-metals. The charge on the ion can also be shown as
and the electron structure written as [2, 8] + The charge on the sodium ion will make it react and form ionic bonds with other oppositely charged ions. The full outer shell of electrons does not make the sodium ion unreactive (see an example). The Reaction between Sodium and Chlorine. Chlorine has 7 electrons in its outer shell. It is in group 7 of the periodic table. When an atom of chlorine reacts it will gain one electron from sodium. The outer shell of chlorine will then have 8 electrons and be full. The chloride ion will have an extra electron and therefore an extra negative charge (shown as a - sign).
The electrostatic force of attraction between the oppositely charged ions is called an ionic bond. The electrons are shown as dots and crosses to show how they have moved during the reaction. In reality all electrons are identical. The balanced chemical equation for the above reaction is Sodium + chlorine sodium chloride. 2Na(s) + Cl2 (g) 2NaCl(s) Sodium chloride is a crystalline ionic compound. It forms a giant structure. Valency, OxidationState and Ionic Compounds. When a metal reacts with a non-metal, the metal will lose electrons to form a positive ion
and the non-metal will gain electrons to form a negative ion. The compound which is formed will be ionic. It will form a giant structure (also called a giant ionic lattice). If you do not know whether an element is a metal or a non-metal see the periodic table The valency (combining power) of a metal is the same as its oxidation state (the charge on the ion). The number of electrons that a metal will lose is the same as its group number in the periodic table. A metal in group 1 will form a 1+ion (Valency 1,oxidation state 1+). A metal in group 2 will form a 2+ion (Valency 2, oxidation state 2+). The number of electrons that a non-metal will gain will be 8 minus its group number. A non-metal in group 6 will form a 2- ion (Valency 2, oxidation state 2-). A non-metal in group 7 will form a 1- ion (Valency 1, oxidation state 1-). A non-metal ion is negative because it has gained electrons Magnesium is in group 2 of the periodic table. A magnesium atom will lose 2 electrons to form a stable 2+ ion.
Oxygen is in group 6of the periodic table. An oxygen atom will gain2 electrons to form a stable 2ion. In this example the electrons are shown as dots and crosses. You will often see electrons drawn like this in books.
The ionic bond between magnesium and oxygen is stronger than the ionic bond between sodium and chlorine because of the greater charge on the ions. Magnesium oxide has a higher melting point because of the stronger bond. magnesium + oxygen magnesium oxide. 2Mg(s) + O2(g) 2MgO(s)
Lithiumis in group 1 of the periodic table. A lithium atom will lose 1 electron to form a stable1+ion. Oxygen is in group 6of the periodic table. An oxygen atom will gain2 electrons to form a stable 2ion. In this example the electrons are shown asdots and crosses. Two lithium atoms will each give one electron to the oxygen atom. The atoms become ions.
The electrostatic attraction between the oppositely charged ions forms the ionic bond between lithium and oxygen. The formula for lithium oxide is Li2O. lithium+ oxygen lithium oxide. 4Li(s) + O2(g) 2Li2O(s)
Magnesium is in group 2 of the periodic table. A magnesium atom will lose 2 electrons to form a stable2+ion. Chlorine is in group 7 of the periodic table. A chlorine atom will gain1 electron to form a stable 1- ion. In this example the electrons are shown asdots andcrosses. Two chlorine atoms will each gain one electron from the magnesium atom. The atoms become ions.
The attraction between the oppositely charged ions forms the ionic bond between magnesium and chlorine. The formula for magnesium chloride is MgCl2. magnesium +chlorine magnesium chloride. Mg(s) + Cl2(g) MgCl2(s) The Electron Structure of Ions andNoble Gases are the Same.
The noble gases are in group 0 of theperiodic table. They will not react with otheratomsbecause they have a fullouter shell of electronsand no overall charge. Atomswhich have lost or gained electrons to form ionswill also have a full outer shell of electrons but because they have a charge they will form ionicbonds with other oppositelycharged ions. Ions and noble gases both have a fullouter shell of electrons and therefore can have thesame electron structure. A Li+ion has thesameelectron structure as Helium. A Mg2+ ion has the same electron structure as a Na+ ion and a O2- ion. It is the electron structure ofNeon (see previous pages). A Cl- ion has the same electron structure as Argon. The electron structure of Helium is 2. Neon is 2, 8. Argon is 2, 8, 8. INamesof Ionic Compounds. The names of metalelements do not change when they become ions.
If you do not know whether anelement is a metal or a non-metal see the periodic table ons are said to have a noble gas electron structure Metalsform positively charged ions called cations. Examples are Li+, Na+, K+, Mg2+, Ca2+, Al3+. The above ions are called lithium, sodium, potassium, magnesium, calcium and aluminium. The names of non-metal elements do change when they become ions. Non-metals formnegatively charged ions called anions. Examples are F-, Cl-, Br-, I-, O2-, S2-. If there is only 1 non-metal in the ionic compound thename ends in ide. The above ions are called fluoride, chloride, bromide,iodide, oxide and sulfide. So, lithium + chlorine lithium chloride. 2Li(s) + Cl2(g) 2LiCl(s) potassium + bromine 2K(s) + Br2(l) 2KBr(s) potassium bromide.
If there are 2 non-metals and the second one is oxygen the name ends in ate. Why is the formula of sodiumoxide Na2O andnot NaO or NaO2?
The ionic solid must have the same number of plus and minuscharges. If Na+ forms a compound with O2-, then the formula will be Na2O. Two sodium ions (each 1+) will be needed to balance the charge on oneoxygen ion (2-). Sodium has valency 1, oxygen hasvalency 2. Examples of formulaeof other ionic compounds from the elements on the previous page are LiF, LiCl, LiBr, LiI, 1+ with 1NaF,NaCl,NaBr,NaI, gives KF,KCl,KBr,KI, 1 to 1. Li2O,Na2O,K2O, 1+with 2Li2S,Na2S,K2S, gives 2 to 1. MgF2, MgCl2, MgBr2, MgI2, 2+with 1CaF2, CaCl2, CaBr2, CaI2, gives 1 to 2. MgO,CaO, MgS, CaS, 2+with 2- gives 1 to 1. AlF3,AlCl3,AlBr3,AlI3, 3+ with 1- gives 1 to 3. Al2O3,Al2S3, 3+ with 2- gives 2 to 3 Below is a small piece of a giant ionic structure. It is also called a giant ionic lattice. The word "giant" means that ahuge number of particles are present (compare this with the word simple). A giant ionic structureis made from a huge numberof ions.
The red balls are positiveions and the blue balls are negativeions. The electrostaticattraction between the oppositely chargedions is called an ionic bond (compare this with a covalent bond).
The structureextends (repeats itself) in all directions giving a crystal with a regular arrangement of ions called a lattice. The crystal is said to be highly ordered. For sodium chloridethe red balls may representNa+ ions and the blue balls may representCl- ions. All ionic solids have a similar structure to thatshown above but they may not beidentical. Differences of packing and the relative size and amounts ofions will give different crystal variations. When metals react withnon-metals they form an ionic compound. Ions have a charge because electrons are lost or gained informing an ionicbond. An ionic compound has strongforces of attraction between the ions in all directions and forms a giantstructure.
Ionicbonds are strong. All ioniccompounds are solid at roomtemperature. Solid ionic compounds do notconduct electricity because the ions are not free tomove. If the solid is heated until it melts, the liquid will conductelectricity because the ions are mobile (they can move). When electricity flows through an ionic compound the ions become separated and turned into elements. This happens during electrolysis. If the ionic solid is dissolved in a solvent (for example water), the particles of the solventovercome the forceof attraction between the ions and separate the ionsfrom each other to form a solution. The solution will conduct electricity because the ions are now free to move. The liquid which conducts electricityis called the electrolyte. What is Covalent Bonding? When non-metals react with non-metals they shareelectrons and form a covalent bond. Covalent means sharing. If you do not know whether an element is a metal or a non-metal, see the periodic table. A covalent bond forms because of the electrostaticattraction between the nucleiof the atoms(that are positive) and the shared electrons (that are negative).
There are noions present (no + or - charges) because the electrons are shared, not transferred from one atom toanother. One pair of shared electrons form asinglecovalent bond. Two pairs of shared electrons form a double covalent bond. Three pairs of shared electrons form a triple covalent bond. Only covalent compounds are called molecules. If the compound is ionic it is not called a molecule. Covalent compounds containing a small number of atoms are called simple molecules.Simple means that only a small number of atomsare present. If a huge number of atoms are present it would be called a giant molecule. Why does a Chlorine Molecule have a Covalent Bond? Chlorine is a non-metal. A chlorine atom has 7electrons in itsouter shell. Chlorine is in group 7 of the periodic table. Two chlorine atoms will eachshare one electron to get a fullouter shell and form a stable Cl2molecule This is a picture of the shared electrons making a covalent bond in a chlorine molecule. Chlorine is a simple molecule.
By sharing the two electrons where the shells touch each chlorine atom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable and the Cl2 molecule will notreact further with other chlorine atoms. One pair of shared electrons form a single covalent bond. There are noions present (no + or - charges) in chlorine gas because the electrons are shared, not transferred from one atom toanother. Chlorine does form hydrogen ions when it is dissolvedin water to become chloric acid. What is a Hydrogen Molecule? Hydrogen is a non-metal.Hydrogen has only oneelectron. Two hydrogen atoms will eachshare their one electron to form a covalent bond and make a hydrogen molecule (H2).
This is a picture of a hydrogen molecule.
By sharing the two electrons where the shells touch each hydrogenatom can count 2 electrons in its outer shell. These full outer shells with their shared electrons are now stable. The H2 molecule will notreact further with other hydrogen atoms. The pair of shared electrons between the two hydrogen atoms form a singlecovalent bond. The structural formula of a hydrogen molecule is written
There are noions present (no + or - charges) in hydrogen gas because the electrons are shared, not transferred from one atom toanother. What is an Oxygen Molecule?
Oxygen is a non-metal. An oxygen atom has 6electrons in itsouter shell. Oxygen is in group 6 of the periodic table. Two oxygen atoms will eachshare two electrons to form twocovalent bondsand make an oxygen molecule (O2). This is a picture of an oxygen molecule.
By sharing the four electrons where the shells touch each oxygen atom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable, and the O2 molecule will not (normally)react further with other oxygen atoms. Note the 2 pairs (4 electrons)shared between the atoms. Each electron pair is one bond. Oxygen has two bondsbetween its atoms. This is called a double bond. The structural formula of an oxygen molecule is written
There are noions present (no + or - charges) in oxygen gas
because the electrons are shared, not transferred from one atom toanother. What is a Carbon Dioxide Molecule? Oxygen and carbon are both non-metals. An oxygen atom has 6electrons in itsouter shell. Oxygen is in group 6 of the periodic table. A carbon atom has 4 electrons in itsouter shell. Carbon is in group 4 of the periodic table. Two oxygen atoms and 1 carbon atom will each sharetwo electrons to formfour covalent bonds and make a carbon dioxide molecule (CO2). This is a picture of a carbon dioxide molecule.
By sharing the four electrons where the shells touch each oxygen and carbonatom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable, and the CO2 molecule will not react further with other oxygenor carbon atoms.
Each electron pair is one bond. Carbon and oxygen have two bonds each between their atoms. This is called a double bond. The structural formula of a carbon dioxide molecule is written
There are noions present (no + or - charges) in carbon dioxide gas because the electrons are shared, not transferred from one atom toanother. Carbon dioxide does form hydrogen ions when it isdissolvedin water (or rain water) to become a weakacid called carbonic acid What are the Properties of SimpleMolecules? (compare these with giantmolecules and ioniccompounds). When non-metals react with non-metals a covalently bonded molecule is formed. Covalent bonds are strong but only exist between the atoms of the molecule. The force of attraction between molecules (called the intermolecular force) is very weak (compare this with ionic bonding). The picture below shows the forces of attraction between two molecules of oxygen gas.
The weak force between molecules means that very little energy is needed to separate them. Many molecular compounds areliquid or gas at roomtemperature. They have low melting andboiling points. Note that when a molecular compound melts or boils, molecules separate from each other but the covalent bond between theatoms of the molecule does not break. The molecule is the same molecule in the solid, liquid orgas state. If the covalent bond breaks, the moleculeis said to decompose (split up!). Molecules do not have a charge (noions) because the electrons areshared between atoms to form acovalent bond. Molecular substances will thereforenot conduct electricity What is a GiantMolecule? - What is Carbon? A covalently bonded substance containing a huge number ofatoms is called a giant molecule or a giant covalentlattice.
There are four examples of molecules (made from nonmetals) which form giant structures. They are silicon, silicon dioxide and two forms of the elementcarboncalled diamondand graphite (polymers are adifferent kind of largemolecule). When two (or more)forms of an element exist in the same physical state, they are called allotropes. Diamond and graphite are allotropes of carbon. Carbon can exist as fullerenes as well as diamond and graphite. Carbon and siliconare both in group 4 of the periodic table. They both need to form 4 bonds withthemselves or other elements. They have valency4. Valency is the combining power of an atom. (with the exception of graphitewhich is a giant molecule). What is the Structure of Diamondand Silicon? Diamond is a formof the elementcarbon - see also graphite.
In the picture of diamond above, eachblue ball represents a carbon atom. The structure has billions of atoms forming hexagons andextends inall directions. Allof the covalent bonds in diamond areidentical. It forms agiantmolecular structure. A crystal of diamond is onegiant molecule! The covalent bonds are very strong.Diamond is the hardest naturally occurring material. It does not conductelectricity. Silicon (used in microchips for computers) has the same structure, with eachblue ballbeing a silicon atom. Silicon dioxide (SiO2) issand (also called silica). SiO2 has a similar structure and also forms a giant molecule. What is theStructure of Graphite?
Whenever you come across carbon, as a reactant or electrode, carbon means graphite notdiamond. It can be written C(gr) but is usually written as just C. Graphite consists of many flat layers of hexagons (like a wire fence). The layers are called graphene sheets. Each carbon atom is joined tothree other carbon atoms. Each layer is itself a giant molecule with very strong covalent bonds. Carbon is in group 4 of the periodic table and so it has four electrons in its outer shell. Three electrons are used forbonding in the graphene sheet. The fourth electron between thelayers is delocalised (it is afree electron).
Between the layers thebonds are weak. Free electrons between the layers allows graphite to conduct electricity and heat.
The layers can easily slide over each other making graphite soft and slippery and anexcellent lubricant (like oil). See also carbon fibresand fullerenes. What are the Properties of GiantMolecules? Giant molecules include diamond,graphite, silicon and silicon dioxide. Giant Molecules have high melting and boiling points due to strong covalent bonds. They are very hard (due to strong covalent bonds). They do not dissolve in water. They do not conduct electricity as a solid (except graphite) or as a liquid because there are no ions What are the Properties of Carbon Fibres? Carbon Fibres are very thin (see nano particles). They are less than one hundredth of a millimeter in diameter. They can be more than three times as strong as steel but with less than one quarter of the density. How is Carbon Fibres Made? Carbon fibres are made by heating long polymer chains containing carbon and other atoms until there is only
carbon left. The chains are heated where there is no oxygen to prevent the carbon atoms reacting to form carbon dioxide. What are the Uses of Carbon Fibres? Carbon fibres are used to reinforce a large number of materials. The materials are mainly polymers called carbon fibre reinforced plastic. The carbon fibres make the polymer stronger. Carbon fibres are used to make an increasingly large number of products including aircraft, cars, boats, sports equipment (fishing rods, tennis rackets, golf clubs) and bicycles. See also graphite and fullerenes. What is Metallic Bonding? Metals form a giant structure (like ionic compounds and giant molecules).
The red balls represent metal ions. The blue lines represent delocalized electrons in the outer shell of the metal ions. Delocalized means that they are not attached to one particular ion. The structure of a metal can also be shown as
In the above picture the dotted lines represent the delocalized electrons.Delocalised electrons are also called free electrons because they can move very easily through the metal structure. It is these free electrons which give metals their properties. It is the free electrons (delocalized electrons) that give metals their properties. 1. The free electrons cause metals to conduct heat and electricity. 2. The free electrons allow the metal ions to slide over each other. This makes metals malleable which means that they are
soft, easily bent and shaped, and can be pressed or beaten into thin sheets. Metals are ductile which means that they can be drawn down into wires. 3. the free electrons hold the structure together as if the metal ions were in”glue" (called a "sea of electrons"). Delocalized electrons hold the ions together by strong electrostatic forces. This gives metals high melting points and boiling points. They are all solid at room temperature except mercury, which is liquid. The properties of a metal can be changed by mixing in other elements to make an alloy.
Revision Questions
The best way to remember the information in this chapter is to get a pen and paper and write down your answers. Atomic Structure
1 2 3 4 5 6 7 8 9 What is an Atom? Which Particles are found in the Nucleus? What is the charge on an Electron? What is the charge on a Neutron? Does a Proton have more mass than a Neutron? Does a Proton have more mass than an Electron? What is the Atomic Number? What is an Isotope? What is the maximum number of Electrons in each Shell? Answer Answer Answer Answer Answer Answer Answer Answer Answer
Ionic Bonding
10 How does an Atom become an Ion? Write the Balanced Equation for the reaction between 11 Sodium and Chlorine. Draw a Dot and Cross diagram for the reaction between 12 Sodium and Chlorine. 13 What is an Ionic Bond? 14 What type of Structure do Ionic Compounds form? 15 A metal in group 1 will form what type of Ion? 16 A non-metal in group 7will form what type of Ion? 17 What is the connection between an Ion and a Noble Gas? What is the name of the Compound made from Lithium 18 and Chlorine? 19 What is the formula of Magnesium Oxide? 20 What is the formula of Aluminum Oxide? 21 Give two Properties of Ionic Compounds? 22 What does the state symbol aq mean? 21 What is the formula of Calcium Carbonate? Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer
Covalent Bonding
22 23 24 25 26 27 28 29 What does Covalent mean? How many Electrons are there in a Single Covalent Bond? When a Compound is called a Molecule? Draw a Dot and Cross diagram for a Chlorine Molecule. Draw a Dot and Cross diagram for an Ammonia Molecule. Draw a Dot and Cross diagram for a Water Molecule. Are Covalent Bonds Strong or Weak? Do Molecular Substances Conduct Electricity? Answer Answer Answer Answer Answer Answer Answer Answer
Giant Molecules
30 31 32 33 34 What is a Giant Molecule? Give one Example of a Giant Molecule? What is an Allotrope? Why does Graphite Conduct Electricity? Give two Properties of a Giant Molecule? Answer Answer Answer Answer Answer
Metallic Bonding
35 What type of Structure does Metals Form? 36 What are Free Electrons? 37 Give two Properties of Metals? Answer Answer Answer
What is an Isotope? Atoms of the same element may have different numbers of neutrons. These are called isotopes. For example, Chlorine (atomic number17) may have 18 or 20 neutrons. The mass number will be either 17 + 18 = 35, or 17+ 20 = 37.
Isotopes of the same element have the same chemical properties because the number of protons and electrons are the same. What are Electron Shells (energy levels)? Electrons in atoms are in shells (shown as circles around the nucleus). The shells can also be called energy levels. We will use the term shell rather than energy level but either is acceptable. The maximum number of electrons in each shell, going from the middle to the outside, is 2, 8, 8, 18. Below is a picture of a potassium atom. Its electron structure is2, 8, 8, 1.
An atom that has the maximum number of electrons in its outer shell will be stable. This means that it will not react with other atoms. It belongs to a group called the noble gases.
The electron shells are said to be full. The inner shells of an atom are always full. If the outer shell of an atom has less than its maximum number of electrons (see potassium above) then it will not be stable. It will react with other atoms to get a full outer shell. Ions also have a full outer shell of electrons but because they have a charge they will react and form ionic bonds with other oppositely charged ions What is the Difference between an Atom and an Ion? An atom has the same number of protons and electrons. An atom has no overall electric charge. If an atom loses or gains electrons it is no longer called an atom. It is called an ion. An ion has a full outer shell of electrons. An ion has an electric charge. Why do Chemical Reactions Happen? All chemical reactions happen because atoms are trying to get a full outer shell of electrons. The total number of atoms is the same before and after the reaction. When an atom reacts with another atom to form a chemical bond
it will either 1. Lose electrons to form a stable positive ion. 2. Gain electrons to form a stable negative ion. Or 3. Share electrons to form a stable molecule What happens when a Sodium Atom becomes a Sodium Ion? A sodium atom has 1 electron in its outer shell. It is in group 1 of the periodic table. When sodium reacts with non-metals (for example chlorine) it will lose its outer electron. Its outer shell will then have no electrons. It is as though the outer shell has vanished. The next shell in is full. This full inner shell becomes the new full outer shell.
The sodium atom loses its outer electron to become a sodium ion. The sodium ion still has 11 protons (11 positive charges) but now only 10 electrons (10 negative charges). The sodium ion has an extra positive charge, shown by
the + sign. All group 1metals will form a 1+ ion when they react with non-metals. The charge on the ion can also be shown as
and the electron structure written as [2, 8] + The charge on the sodium ion will make it react and form ionic bonds with other oppositely charged ions. The full outer shell of electrons does not make the sodium ion unreactive (see an example). The Reaction between Sodium and Chlorine. Chlorine has 7 electrons in its outer shell. It is in group 7 of the periodic table. When an atom of chlorine reacts it will gain one electron from sodium. The outer shell of chlorine will then have 8 electrons and be full. The chloride ion will have an extra electron and therefore an extra negative charge (shown as a - sign).
The electrostatic force of attraction between the oppositely charged ions is called an ionic bond. The electrons are shown as dots and crosses to show how they have moved during the reaction. In reality all electrons are identical. The balanced chemical equation for the above reaction is Sodium + chlorine sodium chloride. 2Na(s) + Cl2 (g) 2NaCl(s) Sodium chloride is a crystalline ionic compound. It forms a giant structure. Valency, OxidationState and Ionic Compounds. When a metal reacts with a non-metal, the metal will lose electrons to form a positive ion
and the non-metal will gain electrons to form a negative ion. The compound which is formed will be ionic. It will form a giant structure (also called a giant ionic lattice). If you do not know whether an element is a metal or a non-metal see the periodic table The valency (combining power) of a metal is the same as its oxidation state (the charge on the ion). The number of electrons that a metal will lose is the same as its group number in the periodic table. A metal in group 1 will form a 1+ion (Valency 1,oxidation state 1+). A metal in group 2 will form a 2+ion (Valency 2, oxidation state 2+). The number of electrons that a non-metal will gain will be 8 minus its group number. A non-metal in group 6 will form a 2- ion (Valency 2, oxidation state 2-). A non-metal in group 7 will form a 1- ion (Valency 1, oxidation state 1-). A non-metal ion is negative because it has gained electrons Magnesium is in group 2 of the periodic table. A magnesium atom will lose 2 electrons to form a stable 2+ ion.
Oxygen is in group 6of the periodic table. An oxygen atom will gain2 electrons to form a stable 2ion. In this example the electrons are shown as dots and crosses. You will often see electrons drawn like this in books.
The ionic bond between magnesium and oxygen is stronger than the ionic bond between sodium and chlorine because of the greater charge on the ions. Magnesium oxide has a higher melting point because of the stronger bond. magnesium + oxygen magnesium oxide. 2Mg(s) + O2(g) 2MgO(s)
Lithiumis in group 1 of the periodic table. A lithium atom will lose 1 electron to form a stable1+ion. Oxygen is in group 6of the periodic table. An oxygen atom will gain2 electrons to form a stable 2ion. In this example the electrons are shown asdots and crosses. Two lithium atoms will each give one electron to the oxygen atom. The atoms become ions.
The electrostatic attraction between the oppositely charged ions forms the ionic bond between lithium and oxygen. The formula for lithium oxide is Li2O. lithium+ oxygen lithium oxide. 4Li(s) + O2(g) 2Li2O(s)
Magnesium is in group 2 of the periodic table. A magnesium atom will lose 2 electrons to form a stable2+ion. Chlorine is in group 7 of the periodic table. A chlorine atom will gain1 electron to form a stable 1- ion. In this example the electrons are shown asdots andcrosses. Two chlorine atoms will each gain one electron from the magnesium atom. The atoms become ions.
The attraction between the oppositely charged ions forms the ionic bond between magnesium and chlorine. The formula for magnesium chloride is MgCl2. magnesium +chlorine magnesium chloride. Mg(s) + Cl2(g) MgCl2(s) The Electron Structure of Ions andNoble Gases are the Same.
The noble gases are in group 0 of theperiodic table. They will not react with otheratomsbecause they have a fullouter shell of electronsand no overall charge. Atomswhich have lost or gained electrons to form ionswill also have a full outer shell of electrons but because they have a charge they will form ionicbonds with other oppositelycharged ions. Ions and noble gases both have a fullouter shell of electrons and therefore can have thesame electron structure. A Li+ion has thesameelectron structure as Helium. A Mg2+ ion has the same electron structure as a Na+ ion and a O2- ion. It is the electron structure ofNeon (see previous pages). A Cl- ion has the same electron structure as Argon. The electron structure of Helium is 2. Neon is 2, 8. Argon is 2, 8, 8. INamesof Ionic Compounds. The names of metalelements do not change when they become ions.
If you do not know whether anelement is a metal or a non-metal see the periodic table ons are said to have a noble gas electron structure Metalsform positively charged ions called cations. Examples are Li+, Na+, K+, Mg2+, Ca2+, Al3+. The above ions are called lithium, sodium, potassium, magnesium, calcium and aluminium. The names of non-metal elements do change when they become ions. Non-metals formnegatively charged ions called anions. Examples are F-, Cl-, Br-, I-, O2-, S2-. If there is only 1 non-metal in the ionic compound thename ends in ide. The above ions are called fluoride, chloride, bromide,iodide, oxide and sulfide. So, lithium + chlorine lithium chloride. 2Li(s) + Cl2(g) 2LiCl(s) potassium + bromine 2K(s) + Br2(l) 2KBr(s) potassium bromide.
If there are 2 non-metals and the second one is oxygen the name ends in ate. Why is the formula of sodiumoxide Na2O andnot NaO or NaO2?
The ionic solid must have the same number of plus and minuscharges. If Na+ forms a compound with O2-, then the formula will be Na2O. Two sodium ions (each 1+) will be needed to balance the charge on oneoxygen ion (2-). Sodium has valency 1, oxygen hasvalency 2. Examples of formulaeof other ionic compounds from the elements on the previous page are LiF, LiCl, LiBr, LiI, 1+ with 1NaF,NaCl,NaBr,NaI, gives KF,KCl,KBr,KI, 1 to 1. Li2O,Na2O,K2O, 1+with 2Li2S,Na2S,K2S, gives 2 to 1. MgF2, MgCl2, MgBr2, MgI2, 2+with 1CaF2, CaCl2, CaBr2, CaI2, gives 1 to 2. MgO,CaO, MgS, CaS, 2+with 2- gives 1 to 1. AlF3,AlCl3,AlBr3,AlI3, 3+ with 1- gives 1 to 3. Al2O3,Al2S3, 3+ with 2- gives 2 to 3 Below is a small piece of a giant ionic structure. It is also called a giant ionic lattice. The word "giant" means that ahuge number of particles are present (compare this with the word simple). A giant ionic structureis made from a huge numberof ions.
The red balls are positiveions and the blue balls are negativeions. The electrostaticattraction between the oppositely chargedions is called an ionic bond (compare this with a covalent bond).
The structureextends (repeats itself) in all directions giving a crystal with a regular arrangement of ions called a lattice. The crystal is said to be highly ordered. For sodium chloridethe red balls may representNa+ ions and the blue balls may representCl- ions. All ionic solids have a similar structure to thatshown above but they may not beidentical. Differences of packing and the relative size and amounts ofions will give different crystal variations. When metals react withnon-metals they form an ionic compound. Ions have a charge because electrons are lost or gained informing an ionicbond. An ionic compound has strongforces of attraction between the ions in all directions and forms a giantstructure.
Ionicbonds are strong. All ioniccompounds are solid at roomtemperature. Solid ionic compounds do notconduct electricity because the ions are not free tomove. If the solid is heated until it melts, the liquid will conductelectricity because the ions are mobile (they can move). When electricity flows through an ionic compound the ions become separated and turned into elements. This happens during electrolysis. If the ionic solid is dissolved in a solvent (for example water), the particles of the solventovercome the forceof attraction between the ions and separate the ionsfrom each other to form a solution. The solution will conduct electricity because the ions are now free to move. The liquid which conducts electricityis called the electrolyte. What is Covalent Bonding? When non-metals react with non-metals they shareelectrons and form a covalent bond. Covalent means sharing. If you do not know whether an element is a metal or a non-metal, see the periodic table. A covalent bond forms because of the electrostaticattraction between the nucleiof the atoms(that are positive) and the shared electrons (that are negative).
There are noions present (no + or - charges) because the electrons are shared, not transferred from one atom toanother. One pair of shared electrons form asinglecovalent bond. Two pairs of shared electrons form a double covalent bond. Three pairs of shared electrons form a triple covalent bond. Only covalent compounds are called molecules. If the compound is ionic it is not called a molecule. Covalent compounds containing a small number of atoms are called simple molecules.Simple means that only a small number of atomsare present. If a huge number of atoms are present it would be called a giant molecule. Why does a Chlorine Molecule have a Covalent Bond? Chlorine is a non-metal. A chlorine atom has 7electrons in itsouter shell. Chlorine is in group 7 of the periodic table. Two chlorine atoms will eachshare one electron to get a fullouter shell and form a stable Cl2molecule This is a picture of the shared electrons making a covalent bond in a chlorine molecule. Chlorine is a simple molecule.
By sharing the two electrons where the shells touch each chlorine atom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable and the Cl2 molecule will notreact further with other chlorine atoms. One pair of shared electrons form a single covalent bond. There are noions present (no + or - charges) in chlorine gas because the electrons are shared, not transferred from one atom toanother. Chlorine does form hydrogen ions when it is dissolvedin water to become chloric acid. What is a Hydrogen Molecule? Hydrogen is a non-metal.Hydrogen has only oneelectron. Two hydrogen atoms will eachshare their one electron to form a covalent bond and make a hydrogen molecule (H2).
This is a picture of a hydrogen molecule.
By sharing the two electrons where the shells touch each hydrogenatom can count 2 electrons in its outer shell. These full outer shells with their shared electrons are now stable. The H2 molecule will notreact further with other hydrogen atoms. The pair of shared electrons between the two hydrogen atoms form a singlecovalent bond. The structural formula of a hydrogen molecule is written
There are noions present (no + or - charges) in hydrogen gas because the electrons are shared, not transferred from one atom toanother. What is an Oxygen Molecule?
Oxygen is a non-metal. An oxygen atom has 6electrons in itsouter shell. Oxygen is in group 6 of the periodic table. Two oxygen atoms will eachshare two electrons to form twocovalent bondsand make an oxygen molecule (O2). This is a picture of an oxygen molecule.
By sharing the four electrons where the shells touch each oxygen atom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable, and the O2 molecule will not (normally)react further with other oxygen atoms. Note the 2 pairs (4 electrons)shared between the atoms. Each electron pair is one bond. Oxygen has two bondsbetween its atoms. This is called a double bond. The structural formula of an oxygen molecule is written
There are noions present (no + or - charges) in oxygen gas
because the electrons are shared, not transferred from one atom toanother. What is a Carbon Dioxide Molecule? Oxygen and carbon are both non-metals. An oxygen atom has 6electrons in itsouter shell. Oxygen is in group 6 of the periodic table. A carbon atom has 4 electrons in itsouter shell. Carbon is in group 4 of the periodic table. Two oxygen atoms and 1 carbon atom will each sharetwo electrons to formfour covalent bonds and make a carbon dioxide molecule (CO2). This is a picture of a carbon dioxide molecule.
By sharing the four electrons where the shells touch each oxygen and carbonatom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable, and the CO2 molecule will not react further with other oxygenor carbon atoms.
Each electron pair is one bond. Carbon and oxygen have two bonds each between their atoms. This is called a double bond. The structural formula of a carbon dioxide molecule is written
There are noions present (no + or - charges) in carbon dioxide gas because the electrons are shared, not transferred from one atom toanother. Carbon dioxide does form hydrogen ions when it isdissolvedin water (or rain water) to become a weakacid called carbonic acid What are the Properties of SimpleMolecules? (compare these with giantmolecules and ioniccompounds). When non-metals react with non-metals a covalently bonded molecule is formed. Covalent bonds are strong but only exist between the atoms of the molecule. The force of attraction between molecules (called the intermolecular force) is very weak (compare this with ionic bonding). The picture below shows the forces of attraction between two molecules of oxygen gas.
The weak force between molecules means that very little energy is needed to separate them. Many molecular compounds areliquid or gas at roomtemperature. They have low melting andboiling points. Note that when a molecular compound melts or boils, molecules separate from each other but the covalent bond between theatoms of the molecule does not break. The molecule is the same molecule in the solid, liquid orgas state. If the covalent bond breaks, the moleculeis said to decompose (split up!). Molecules do not have a charge (noions) because the electrons areshared between atoms to form acovalent bond. Molecular substances will thereforenot conduct electricity What is a GiantMolecule? - What is Carbon? A covalently bonded substance containing a huge number ofatoms is called a giant molecule or a giant covalentlattice.
There are four examples of molecules (made from nonmetals) which form giant structures. They are silicon, silicon dioxide and two forms of the elementcarboncalled diamondand graphite (polymers are adifferent kind of largemolecule). When two (or more)forms of an element exist in the same physical state, they are called allotropes. Diamond and graphite are allotropes of carbon. Carbon can exist as fullerenes as well as diamond and graphite. Carbon and siliconare both in group 4 of the periodic table. They both need to form 4 bonds withthemselves or other elements. They have valency4. Valency is the combining power of an atom. (with the exception of graphitewhich is a giant molecule). What is the Structure of Diamondand Silicon? Diamond is a formof the elementcarbon - see also graphite.
In the picture of diamond above, eachblue ball represents a carbon atom. The structure has billions of atoms forming hexagons andextends inall directions. Allof the covalent bonds in diamond areidentical. It forms agiantmolecular structure. A crystal of diamond is onegiant molecule! The covalent bonds are very strong.Diamond is the hardest naturally occurring material. It does not conductelectricity. Silicon (used in microchips for computers) has the same structure, with eachblue ballbeing a silicon atom. Silicon dioxide (SiO2) issand (also called silica). SiO2 has a similar structure and also forms a giant molecule. What is theStructure of Graphite?
Whenever you come across carbon, as a reactant or electrode, carbon means graphite notdiamond. It can be written C(gr) but is usually written as just C. Graphite consists of many flat layers of hexagons (like a wire fence). The layers are called graphene sheets. Each carbon atom is joined tothree other carbon atoms. Each layer is itself a giant molecule with very strong covalent bonds. Carbon is in group 4 of the periodic table and so it has four electrons in its outer shell. Three electrons are used forbonding in the graphene sheet. The fourth electron between thelayers is delocalised (it is afree electron).
Between the layers thebonds are weak. Free electrons between the layers allows graphite to conduct electricity and heat.
The layers can easily slide over each other making graphite soft and slippery and anexcellent lubricant (like oil). See also carbon fibresand fullerenes. What are the Properties of GiantMolecules? Giant molecules include diamond,graphite, silicon and silicon dioxide. Giant Molecules have high melting and boiling points due to strong covalent bonds. They are very hard (due to strong covalent bonds). They do not dissolve in water. They do not conduct electricity as a solid (except graphite) or as a liquid because there are no ions What are the Properties of Carbon Fibres? Carbon Fibres are very thin (see nano particles). They are less than one hundredth of a millimeter in diameter. They can be more than three times as strong as steel but with less than one quarter of the density. How is Carbon Fibres Made? Carbon fibres are made by heating long polymer chains containing carbon and other atoms until there is only
carbon left. The chains are heated where there is no oxygen to prevent the carbon atoms reacting to form carbon dioxide. What are the Uses of Carbon Fibres? Carbon fibres are used to reinforce a large number of materials. The materials are mainly polymers called carbon fibre reinforced plastic. The carbon fibres make the polymer stronger. Carbon fibres are used to make an increasingly large number of products including aircraft, cars, boats, sports equipment (fishing rods, tennis rackets, golf clubs) and bicycles. See also graphite and fullerenes. What is Metallic Bonding? Metals form a giant structure (like ionic compounds and giant molecules).
The red balls represent metal ions. The blue lines represent delocalized electrons in the outer shell of the metal ions. Delocalized means that they are not attached to one particular ion. The structure of a metal can also be shown as
In the above picture the dotted lines represent the delocalized electrons.Delocalised electrons are also called free electrons because they can move very easily through the metal structure. It is these free electrons which give metals their properties. It is the free electrons (delocalized electrons) that give metals their properties. 1. The free electrons cause metals to conduct heat and electricity. 2. The free electrons allow the metal ions to slide over each other. This makes metals malleable which means that they are
soft, easily bent and shaped, and can be pressed or beaten into thin sheets. Metals are ductile which means that they can be drawn down into wires. 3. the free electrons hold the structure together as if the metal ions were in”glue" (called a "sea of electrons"). Delocalized electrons hold the ions together by strong electrostatic forces. This gives metals high melting points and boiling points. They are all solid at room temperature except mercury, which is liquid. The properties of a metal can be changed by mixing in other elements to make an alloy.
Revision Questions
The best way to remember the information in this chapter is to get a pen and paper and write down your answers. Atomic Structure
1 2 3 4 5 6 7 8 9 What is an Atom? Which Particles are found in the Nucleus? What is the charge on an Electron? What is the charge on a Neutron? Does a Proton have more mass than a Neutron? Does a Proton have more mass than an Electron? What is the Atomic Number? What is an Isotope? What is the maximum number of Electrons in each Shell? Answer Answer Answer Answer Answer Answer Answer Answer Answer
Ionic Bonding
10 How does an Atom become an Ion? Write the Balanced Equation for the reaction between 11 Sodium and Chlorine. Draw a Dot and Cross diagram for the reaction between 12 Sodium and Chlorine. 13 What is an Ionic Bond? 14 What type of Structure do Ionic Compounds form? 15 A metal in group 1 will form what type of Ion? 16 A non-metal in group 7will form what type of Ion? 17 What is the connection between an Ion and a Noble Gas? What is the name of the Compound made from Lithium 18 and Chlorine? 19 What is the formula of Magnesium Oxide? 20 What is the formula of Aluminum Oxide? 21 Give two Properties of Ionic Compounds? 22 What does the state symbol aq mean? 21 What is the formula of Calcium Carbonate? Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer Answer
Covalent Bonding
22 23 24 25 26 27 28 29 What does Covalent mean? How many Electrons are there in a Single Covalent Bond? When a Compound is called a Molecule? Draw a Dot and Cross diagram for a Chlorine Molecule. Draw a Dot and Cross diagram for an Ammonia Molecule. Draw a Dot and Cross diagram for a Water Molecule. Are Covalent Bonds Strong or Weak? Do Molecular Substances Conduct Electricity? Answer Answer Answer Answer Answer Answer Answer Answer
Giant Molecules
30 31 32 33 34 What is a Giant Molecule? Give one Example of a Giant Molecule? What is an Allotrope? Why does Graphite Conduct Electricity? Give two Properties of a Giant Molecule? Answer Answer Answer Answer Answer
Metallic Bonding
35 What type of Structure does Metals Form? 36 What are Free Electrons? 37 Give two Properties of Metals? Answer Answer Answer
