Solid State

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SOLID STATE CHEMISTRY
http://chemistry.tutorvista.com/inorganic-chemistry/types-of-solids.html
https://books.google.co.in/books?
id=QHZyoKCxwKAC&pg=PA364&dq=interfacial+
+angles+in+a+crystal&hl=en&sa=X&ved=0ahUKEwjW1cXZ9PTKAhWDRI4K
HXmLBnkQ6AEISzAI#v=onepage&q=interfacial%20%20angles%20in%20a
%20crystal&f=true

Matter is made of a large number of particles, which have space between
them. These particles are continuously in motion and attract each other. You
know that all forms of matter are made of billions of particles. The same can
be said of solid, liquid and gaseous states of matter. All forms of matter show
the following properties:

There is some intermolecular space between particles of matter.

Irrespective of the state, particles of matter are continuously moving. They
can be said to possess kinetic energy.

Particles of matter are constantly attracted to each other. It is this force of
attraction that keeps the particles together.

Matter around us exists in different states: solids, liquids, gases, plasma and
the Bose Einstein Condensate (BEC). Since matter exists as tiny particles,
let’s compare three states of matter – solid, liquid and gaseous - to see the
arrangement of these particles. The arrangement of particles in each type of
matter determines its physical properties.

Let’s see how it is in the solid state of matter. What do you observe when you
see an ice cube or any other form of solid matter? Solid matter shows definite
shape and volume. Solids can maintain their shape even on the application of
force or pressure. Let’s discuss some other properties of solid state.

Solids State Characterization
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A solid is defined as that form of matter which possesses rigidity and hence
possesses a definite shape and a definite volume.

Free movement of particles in the gaseous state and in the liquid state is the
reason for their fluidity which is due to weaker intermolecular forces while the
particles in the solid state are held together with strong intermolecular forces
and don’t possess translator motion.

They can only vibrate about their fixed position. Therefore, solids are rigid
and have definite shape.
General Characteristic of Solids

The general characteristics of solids are as follows. As mentioned above,
solids have two main properties.

They have strong intermolecular forces and short internuclear distance due
to close packing of constituent particles.
Their constituent particles don’t possess translator motion but can oscillate
only around their mean position.

Due to these two basic properties, solids possess the following characteristic
properties.

They have definite shape, mass and volume.
They are rigid and incompressible.

They have high density.

The solids are classified into two main types.
Crystalline Solids - All solid metals, nonmetals and compounds come in this
category.
Amorphous Solids - Rubber, glass, pitch, polymers of high molecular mass,
quartz glass, etc., are the examples of it.
Crystalline Solids
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These are the substances whose constituent particles possess a regular
orderly arrangement. They are considered as true solids. For example, NaCl
(rock salt), Sucrose (sugar), Diamond, Quartz, etc.

The main properties of these solids are mentioned below.

1. Arrangement of constituents particles

In a crystalline solid, the particles (ion, molecule or atoms) are arranged in
definite geometric pattern in the three dimensional network. This is known as
long range order. This arrangement repeats periodically over the entire
crystal. Due to this arrangement, they have short range as well as long range
order.

Cubic Arrangement of solids

2. Melting point

The crystalline solids have a sharp melting point, so possess definite heat of
fusion.

3. Anisotropy

In a crystalline solid, the properties like electrical conductance, refractive
index, thermal expansion, etc., have different values in different directions.

This type of behavior is called Anisotropy and the substances with this
property are called Anisotropic.

Anisotropic Behavior Of Crystalline Solids

4. Clean Cleavage with knife

A crystalline solid gives a clean surface after cleaving it with a knife rather
than an irregular breakage.

Classification of crystalline solids

They can be classified into different categories depending upon the type of
constituent particles and the nature of intermolecular forces between them.
Various categories are:

Ionic solid
Molecular Solids
Covalent or Network Solids
Metallic Solids

Ionic Solids

In the ionic solids, the constituent particles are anions and cations. Each
participating ion is surrounded by a typical number of opposite charges. The
number of ions that surround a particular ion of the opposite charge is called
the coordination number of the ion.

For example, in NaCl crystal, each Na+ ion is surrounded by 6 Cl- ions and
each Cl- ion is surrounded by 6 Na+ ions. So, the coordination number of Na+
and Cl- is 6. Similar in CaF2 crystal, the coordination number of Ca+ and Fions are 8 and 4 respectively. Some other examples are CaCl, ZnS etc. These
ions are held together with strong electrostatic force of attraction.
Some common characteristics of ionic solids are given below.

They have high melting point and boiling point due to strong electrostatic
force of attraction.
In the solid state, they behave like an electrical insulator as the ions are
not free to move, but in an aqueous solution, they are good conductors of
electricity because the ions become free.
They are generally soluble in a polar solvent but not in a non-polar solvent.
They are hard and brittle because their stability depends upon the
preservation of their geometric pattern.

Ionic Solid Caf2

Molecular Solids

In these solids the particles are molecules. Depending upon the nature of the
molecules they are further divided into three types.

1. Non-Polar Molecular Solids -They possess the particles either atoms like
those of noble gases or non-polar molecules like H2, Cl2 I2 etc. The attractive
force between them is weak van der Waal force or dispersion force.
Due to this weak force, they have low melting and boiling points, are soft in
nature and non-conductors of electricity (no ions are present).
They are generally gaseous or liquid in nature at room temperature and
pressure.

Non Polar Molecular Solids

2. Polar Molecular Solids - These are those solids in which constituent
particles are polar molecules like HCl, SO2, etc., the force which held them
together is dipole-dipole force of attraction. This force is stronger than the
dispersion force of non polar molecular solids.

Polar Molecular Solids

These solids are soft, non conductors of electricity and exist in gaseous or
liquid form at room temperature and pressure. Their melting and boiling point
is higher than non-polar molecular solids but not so much.

3. Hydrogen-bonded molecular solids - In these types of solids, the
constituent particles are bonded with hydrogen bond. For example, H2O,
NH3, HF, etc.
So they possess the strong hydrogen bond as intermolecular force. Due to
this, they have a high melting and boiling point which are higher than the
other two types of molecular solids. They exist as volatile liquid or soft solids
at room temperature and pressure.

Hydrogen Bonded Molecular Solids

Covalent or Network Solids

In this type of solids the constituent particles are atoms of the same or
different elements connected to each other by covalent bond.
So a network of covalent bonds is formed throughout the crystal and they
form a giant molecule.
The most common example is diamond, silicon carbide (SiC) and graphite,
etc.
Network Solids

Covalent Solids

Due to strong covalent bonds, they are hard and brittle and have high
melting and boiling points. They are insulators but graphite is exception in
this case because of the free fourth electron of each carbon atom where each
carbon atom is linked to three neighboring carbon atoms. So graphite is good
conductor of electricity.

The distance between the adjacent layers is greater than carbon-carbon bond
length. These layers are not bonded to each other and can easily slip over
each other. This is the reason for the softness and good solid lubricant
behavior of graphite.

Metallic Solids
These solids contain metal atoms as constituent particles. As metals have a
good tendency to lose their valence electron and change in to positively
charged metal ions (kernel). These electrons can easily move throughout the
whole crystal and form the sea of free electrons. So the attractive force
between the kernels and mobile valence electrons is termed as metallic bond.
This is the force which holds the metal ions together.

Metallic Solids

Because of these strong metallic bonds, metals can maintain a regular
structure and usually have high melting and boiling points.
They possess high electrical and thermal conductivity because the free
electrons flow with a charge or heat energy through the metal.

The free electrons allow metal atoms to slide over each other and can be
easily deformed, so metals are malleable and ductile. They possess bright
luster and color due to free electrons. All the metals and alloys come in this
category.
Amorphous Solids
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These are the substances whose constituent particles don't possess a regular
orderly arrangement. The main properties of these solids are mentioned
below:

1. Arrangement of constituents particles

In an amorphous solid, the particles are arranged in a regular manner up to a
small region only. This is called short range order. So, in these solids, the
particles are not in regular arrangement and possess only short range order
and have irregular shape.

Amorphous Solids

2. Melting point

The amorphous solids melt gradually over a temperature range, so do not
possess definite heat of fusion.

3. Isotropy

In amorphous solids, the various physical properties like electrical
conductivity, refractive index, thermal expansion, etc., are same in all
directions just like liquids and gases. This type of behavior is called isotropy
and the substances with this property are called isotropic. So they are
isotropic in nature due to random arrangement of particles.

4. Clean Cleavage with knife

Like a crystalline solid they don't give a clean surface after cleavage with
knife.
They undergo an irregular breakage.

5. Super cooled liquid

They have a tendency to flow like liquid, although very slowly, so they are
also called super cooled liquids. This tendency is illustrated by the fact that
glass panes in the window of old historical buildings are found to be thicker at
the bottom than at the top.

6. Pseudo solids

They are not considered true solids. Due to short range order, small parts of
amorphous solids may be crystalline and rest may be non-crystalline. This
part of amorphous solids is called crystallizes.
So they are also known as pseudo solids. This is the reason for the milkiness
of window glass of old buildings because due to heating during the day and
cooling at nights, glass acquires some crystalline character.

Uses of amorphous solids

Amorphous solids are very useful materials. Here are a few applications of it:

Amorphous solids glass and plastics are very useful materials and are
widely used in construction, house ware, laboratory ware, etc.
Amorphous silica is one of the best materials for converting sunlight into
electricity (photovoltaic).
Amorphous solid rubber is used in making tyres, shoe soles etc.

Comparison between Crystalline Solids and Amorphous Solids
CRYSTALLIINE



Crystals have definite and regular geometry and have long range as
well as short range order of constituent particles.



Crystals posses high melting points.



The crystals external forms have regularity when these are formed.



They give a clean surface after cleavage with knife.



They have definite heat of fusion.



Crystalline solids are very rigid and their molecules cannot be
deformed by mild distorting force.



Crystalline solids are considered as true solid.



Crystalline solids display anisotropism.

AMORPHOUS



The particles in the constituent are arranged irregularly. They do not
have any definite geometry and have short range order.



They are devoid of sharp melting points



No external regularity in their form when these amorphous solids are

formed.



Usually the amorphous solids exhibit irregular cut.



Amorphous solids do not possess any particular heat of fusion.



Amorphous solid do not exhibit rigidity. Deformation could be done by
bending or compressing them.



Amorphous solids are considered as super cooled liquids or also
pseudo solids.



Amorphous solids display isotropism.

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