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Matter is any thing or substance that has mass and occupies volume. There are three types of matter. They are solid, liquid, and gas. The state of a substance depends on the intermolecular forces acting between the molecules, and the thermal energy of the molecules.
Intermolecular Forces
Intermolecular forces are the forces of attraction between atoms, molecules, and ions. These forces hold the covalently bonded molecules together. Intermolecular forces are also called van der Waals forces.
Van der Waals forces
Van der Waals forces are weak intermolecular forces that involve attraction and repulsions between atoms and molecules, and surfaces. These forces form from interactions between uncharged atoms/molecules.
Types of van der Waals forces are as follow:
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Dipole-dipole forces
Dipole-dipole forces are the attractive forces between oppositely charged ends of polar molecules .
Factors that affect dipole-dipole forces:
(i) Electronegativity difference: More the electronegativity difference,more will be dipole-dipole forces.
(ii) Intermolecular distance: Liquids contain strong forces due to less distance between molecules. Gas contains weak forces due to greater distance between molecules.
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Dipole-induced dipole forces
This type of forces operate between a polar molecule which has a permanent dipole and a nonpolar molecule whose electron density is symmetrical.
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London dispersion forces
London dispersion force is the attractive force between the temporary dipole in a molecule and the dipole temporarily induced into an adjacent molecule. It is the weakest among all intermolecular forces. It is present between any two molecules when they are nearly touching.
Hydrogen bonding
Hydrogen bonding is a special type of dipole-dipole interaction. But the difference is that for hydrogen bonding there is a large difference in the electronegativity of the covalently bonded atoms. That means hydrogen bonds are formed between the highly polar N – H ,O – H, H-F bonds. Thus, hydrogen bonding in the force of attraction between the hydrogen atom attached to the highly electronegative atom and the electronegative atom of the other polar molecule.
Gaseous Laws
(1) Boyle’s Law
According to Boyle’s Law, “The volume of a given mass of gas is inversely proportional to pressure at constant temperature.”
Ρ ∝ 1 /V ..(at constant T and n)
P= K x 1/V
where k is the proportionality constant.
(2) Charles Law
According to Jacques Charles, or Charles’ law, “The volume of a given mass of gas is directly proportional to its absolute temperature at constant pressure.”
V ∝ T…..(at constant P)
V = kT
where k is the proportionality constant.
(3) Gay Lussac’s Law
Gay Lussac’s Law states that at constant volume, the pressure of a fixed mass of a gas is directly proportional to the Kelvin temperature. The law is expressed as follows –
P ∝ T….(at constant V)
P=kT
where k is the proportionality constant.
(4) Avogadro’s Law
According to Avogadro’s Law, “Equal volumes of all gases at same temperature and pressure contain equal numbers of molecules”.
V ∝ n
V = kn
where k is the proportionality constant.
Ideal Gas Equation
According to ideal gas equation,
PV = nRT
Where R is the proportionality constant called the universal gas constant.
Dalton’s Law of Partial Pressure
John Dalton gave a law which states that “the total pressure exerted by a mixture of non reacting gases is equal to the sum of partial pressure of each gas present in the mixture”.
Partial Pressure: It is the pressure exerted by a constituent gas of the gaseous mixture when kept alone in the same container. Suppose there are three non-reacting constituting gases 1, 2 and 3 whose partial.
Pressures are P1, P2, P3 respectively. Then, mathematically, Dalton’s Law of partial pressure can be
P Total = P₁ + P₂ + P₂ +……(at constant T, V)
Kinetic Theory of Gases
The postulates of kinetic theory of gases are given below:
- Every gas contains a large number of very small particles called molecules.
- The molecules of a gas move randomly , colliding among themselves and with the walls of the container and change their directions.
- Gas exerts pressure due to the collisions of molecules with the walls of a container. The collisions are perfectly elastic.
- The molecules of a gas are widely separated from one another and there are adequate empty spaces among them.
Compressibility factor (Z)
it determines which extent the real gas deviates for ideal gas behaviour.
Z = PV/nRT
- i) Z >1, positive deviation. less compressibility.
- ii) Z <1 Negative deviation, more compressibility.
Boyle Temperature: The temperature at which a real gas behaves like an ideal gas over an appreciable range of pressure.
Van der Waals Equation
Van der Waal suggested a modified gas equation to describe the behaviour of real gases over a wider range of pressure and temperature. If ‘n’ moles of gas are present in volume ‘V’, then
(P + an²/V2 ) (V – nb) = nRT
Graham’s Law of Diffusion
Diffusion is the process of intermoing of two or more gases irrespective of density relationship, gravity and without the help of external agency.
According to Graham’s Law “at constant pressure and temperature, the rate of diffusion or effusion of a gas is inversely proportional to the square root of its vapour density or molecular mass”.
r ∝ (1/d)½
Liquefaction of Gases
The liquefaction of the gases is the physical conversion of a liquid state gas (condensation).
Critical Temperature
Critical temperature of a gas is the temperature above which the gas cannot be liquefy however high the pressure is applied on the gas.
Tc= 8a/27Rb
Critical Pressure: The minimum pressure that must be applied on a gas at its critical temperature to just liquefy it is known as critical pressure.
Pc= a/27b2
Critical Volume: The volume occupied by one mole of a gas at its critical temperature and critical pressure is known as the critical volume.
Vc = 3b
Liquid State
Introduction
The intermolecular forces in the liquid state are stronger than in the gaseous state. Also their density is higher than that of gases.
Vapour pressure
The pressure that is exerted by the vapour present in equilibrium with a liquid in a closed vessel at a particular temperature is called vapour pressure.
Factors that affects vapour pressure are :
(i) Nature of the liquid: Weaker are the intermolecular forces, higher is the vapour pressure. (ii) Temperature: Higher the temperature, greater is the vapour pressure.
Surface tension of liquids
The force acting at right angles to the surface along 1cm length of the surface is called surface tension. Its units are dynes cm or Nm.
Surface energy of a liquid
The work required to be done to extend the surface area of the liquid by 1 sq. cm or 1 sq. m. is called the surface energy of the liquid. The spherical shape of drops, fire polishing of glass, rise of a liquid in a capillary tube are all examples of force of surface tension.
Factors affecting surface tension :
(i) Nature of the liquid: Greater the intermolecular forces of attraction, higher is the surface tension.
(ii) Temperature: Surface tension decreases with increase of temperature .
Viscosity of liquids
The internal resistance of a liquid to flow or it is the force of friction which one part of the liquid offers to another part of the liquid is called viscosity of liquids. For two layers
F ∝ Adv/dx f=ηAdv/dx
A= area of each surface
dx=distance
dv= velocity difference
where η is called the coefficient of viscosity.
Let A = 1 cm², dx =1 cm and dv = 1 cm s-1 ,f = η . Hence, coefficient of viscosity is the force of friction required to maintain a velocity difference of 1 cm s-1 between two parallel layers 1 cm apart and each having area 1 cm².
Factors affecting viscosity
(i) Nature of the liquid: Greater the intermolecular forces, higher is the viscocity.
(ii) Temperature: Viscosity of a liquid decreases with increase of temperature.
Solid State
The third state of matter we will discuss is solid. Solids have fixed shape and volume. Rigidity, incompressibility, slow diffusion and mechanical strength are some of its characteristics . They are classified into two types :
(a) Crystalline solids
(b) Amorphous solids .
A regular 3D arrangement of points in space is known as space lattice or crystal lattice. There are only 14 three-dimensional lattices known as Bravais lattices. There are 7 lattice systems i.e triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, and cubic.
Unit cell
A unit cell is the smallest unit of the crystal which represents the crystal of the given substance.
There are three types of unit cells:
(a) Primitive or simple cube
(b) Body-centred cube
(c) Face-centred cube
Density of unit cell
The density of the unit cell = Mass of unit cell/Volume of unit cell
Defects
Imperfection or defects is any disruption from a perfectly ordered arrangement of atoms or ions in crystals. These are of two types:
(a) Point defects (b) Line defects
Schottky defects occur when a pair of ions of opposite charge leave the ideal lattice. IT lowers the density of a crystal, e.g., AgBr.
Frenkel defects occur when ion (usually cation) leaves its place in the lattice, creating a vacancy in the crystal.
Non-stoichiometric defects is the defect in which the ratio of cation and anion becomes different from the ideal chemical formula.
In this type of defect the chemical formula and structural formula can not be the same i.e number of cation and anion is unbalanced.
Depending on their reaction of solid to magnetic field, the substances are classified as:
(i) Paramagnetism
Substances which are weakly attracted by the magnetic field are called paramagnetic substances. They lose their magnetism in the absence of a magnetic field. Their magnetic character does not depend on temperature.
(ii) Diamagnetism
Substances that are weakly repelled by magnetic fields are called diamagnetic substances.
Conclusion
Matter is any thing or substance that has mass and occupies volume. There are three types of matter. They are solid, liquid, and gas. John Dalton gave a law which states that “the total pressure exerted by a mixture of non reacting gases is equal to the sum of partial pressure of each gas present in the mixture”. The force acting at right angles to the surface along 1cm length of the surface is called surface tension. Its units are dynes cm or Nm.
