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5. STATES OF MATTER
Matter is anything that occupies space and has a definite mass. Matter mainly exists in three different
states – solid, liquid and gaseous state.
Solids have a definite shape and definite volume. This is because in solids the particles are closely
packed and so the intermolecular force of attraction is greater.
Liquids have no definite shape but have definite volume. In liquids, the intermolecular force of
attraction is smaller than that in solids. So the particles do not have a fixed position.
Gases have no definite shape and volume. Here the particles are far apart and hence they have no
force of attraction.
Comparison between the three states of matter
Properties Solid state Liquid state Gaseous state
Shape and volume Have definite No definite shape but have Have no
shape and definite volume definite shape
volume and volume
Inter molecular force of Strong In between solids and gases Very small
attraction
Arrangement of Closely packed Loosely packed Far apart
particles
K.E of particles Very low In between solids and gases Very high
Diffusability Very low In between solids and gases Very high
Compressibility Very low In between solids and gases Very high
INTERMOLECULAR FORCES
Intermolecular forces are the forces of attraction and repulsion between interacting particles (atoms
and molecules). Attractive intermolecular forces are known as van der Waals forces. These forces include
dispersion forces or London forces, dipole-dipole forces, and dipole-induced dipole forces. A particularly strong
type of dipole-dipole interaction is hydrogen bonding.
1) Dispersion Forces or London Forces
Atoms and non-polar molecules are electrically symmetrical and have no dipole moment. But in an
atom, at a particular moment, the nucleus is shifted towards one side and the electrons, to the other side. So
a temporary dipole (momentarily dipole) is created. This results in the development of instantaneous dipole
on the adjacent atom for a very short time. These temporary dipoles of atoms attract each other. This force of
attraction between temporary dipoles is termed as London forces or dispersion forces. These forces are
important only at short distances.
2) Dipole - Dipole Forces
Dipole-dipole forces act between the molecules possessing permanent dipole (polar molecules). These
molecules interact with the neighbouring molecules. This interaction is stronger than the London forces but is
weaker than ion-ion interaction because only partial charges are involved. The attractive force decreases with
the increase of distance between the dipoles. E.g.: HCl
3) Dipole–Induced Dipole Forces
This type of attractive forces operates between the polar molecules and the non-polar molecules.
Permanent dipole of the polar molecule induces dipole on the electrically neutral molecule by deforming its
electronic cloud. Thus an induced dipole is developed in the other molecule. The attraction between these
molecules is termed as dipole – induced dipole force.
ANIL KUMAR K L ,GHSS ASHTTAMUDI,KOLLAM States of Matter Page 1
, Gas Laws
These are some relationships connecting the measurable properties of gases like pressure (P), temperature
(T), volume (V) and number of moles (n). These are:
1) Boyle’s Law (Pressure – Volume Relationship)
It states that at constant temperature, the volume of a fixed mass of gas is inversely proportional to its
pressure. Mathematically,
P α 1/V
P = k x 1/V, where k is the proportionality constant.
Or, PV = k, a constant
Consider a fixed amount of gas at constant temperature T. Let V1 & P1 are its initial volume and
pressure respectively. Let the gas undergoes expansion, so that its final volume and pressure becomes V2 and
P2.
Then according to Boyle’s law,
P1V1 = P2V2
If we plot graphs between pressure against volume, pressure against 1/volume and PV against P at
constant temperature, the graphs obtained are as follows:
P P PV
PV = a constant
V 1/V P
These graphs are obtained at constant temperature and are called isotherms.
We know that density = mass/volume
i.e., d = m/V
If we put value of V in this equation from Boyle’s law equation, we get the relationship,
d = (m/k) x p
i.e. At constant temperature, pressure is directly proportional to the density of a fixed mass of the gas.
2) Charles’ Law (Temperature – Volume Relationship)
It states that at constant pressure, volume of a fixed mass of gas is directly proportional to its
temperature.
Mathematically, V α T
Or, V=kxT
Or, V/T = k, a constant
Consider a fixed amount of gas at constant pressure P. Let V1 be its volume at a temperature T1 and V2
be its volume at a temperature T2.
Then according to Charle’s law:
V1/T1 = V2/T2
If volume is plotted against temperature at constant pressure, the graph obtained is as follows.
ANIL KUMAR K L ,GHSS ASHTTAMUDI,KOLLAM States of Matter Page 2
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