🌍 Introduction to States of Matter
Matter exists in four states
- Solid
- Liquid
- Gas
- Plasma
The simplest form of matter is the gaseous state.
Most of matter around us is in the solid state.
Liquids are less common than solids, gases and plasmas.
The reason is that the liquid state of any substance can exist only within a relatively narrow range of temperature and pressure.
🌟 Fun Fact: Plasma is the most common state of matter in the universe, making up stars including our Sun!
💨 5.1 Properties of Gases
Definite shape and volume
Gases do not have a definite shape and volume. The volume of a gas is the volume of the container.
Compressibility
The molecules of gases are widely separated from one another and most of the volume of the gas is empty space (nearly 99.9%). That is why gases can be compressed easily.
Joule-Thomson effect
When sudden expansion of gases occurs, cooling takes place. It is called Joule Thomson effect.
Pressure of a gas
Pressure of a gas is due to the collisions of gas molecules with the walls of the container.
Strength of intermolecular forces
There are negligible intermolecular forces in ideal gases.
💧 5.3 Properties of Liquids
Diffusion
Liquids also diffuse like gases, however the rate of diffusion in liquids is much lower than that in gases.
Little empty spaces
There are little empty spaces among liquid molecules because of relatively stronger intermolecular forces.
Compressibility
Liquids are 105 times less compressible than gases, but about 10 times more compressible than solids.
State of motion
The molecules of a liquid are in constant random motion, but their speed of movement is lower than gases.
Kinetic energy
According to kinetic molecular theory, molecules of a liquid are in constant motion, therefore they possess a certain amount of kinetic energy at any temperature.
Example: A liquid is converted into a solid by decreasing its kinetic energy (on cooling) and converted into vapour by increasing kinetic energy (on heating).
🧊 5.11 Solids
General Properties of Solids
Solids are those substances which are rigid, hard, have definite shape and definite volume.
The atoms, ions and molecules that make up a solid are closely packed. They are held together by strong cohesive forces.
Compression of solids
The particles of solids cannot move closer to each other unlike gases. The compression of solids is not possible.
Expansion of solids
Increase in temperature of solids hardly increases their volume. No doubt, there are parameters like coefficient of linear and cubic expansions of various solids, but these are negligible as compared to liquids and gases.
Motion of particles in solids
The constituent particles of a solid do not undergo translatory motion, and neither rotational ones. They only vibrate about their mean positions.
Kinetic energy based on KMT
Solid particles have only vibratory motion and they do not have translational or rotational motion. Therefore, the only kinetic energy that solids possess is vibrational kinetic energy.
🧲 5.4 Intermolecular Forces
Three types of intermolecular forces
- Instantaneous dipole-induced dipole forces (id-id) (London dispersion forces)
- Permanent dipole- permanent dipole forces (pd- pd)
- Hydrogen bonding
Instantaneous Dipole-induced Dipole Forces (id-id)
The momentary force of attraction between an instantaneous dipole and an induced dipole is called instantaneous dipole-induced dipole force.
These are only forces that exist among the molecules of non-polar compounds.
Factors affecting strength: Molecular mass and size, Surface area (shape of molecule).
Permanent Dipole-Permanent Dipole Forces (pd-pd)
The force of attraction between the positive end of a polar molecule and the negative end of a nearby polar molecule is called permanent dipole-permanent dipole force.
Examples: HCl, CHCl₃ (chloroform).
Hydrogen Bonding
Hydrogen bond is a special type of dipole-dipole force. It is the strongest force among intermolecular forces, but is weaker than all the major types of bond.
Conditions for H-bonding:
- The hydrogen atom is connected to a highly electronegative atom (F, O, or N).
- The electronegative atom must have a lone pair of electrons on it.
Examples: H₂O, NH₃, HF.
🚀 Study Strategies
Understand Intermolecular Forces
Create a comparative chart of the three types of intermolecular forces: London dispersion, dipole-dipole, and hydrogen bonding. Note their relative strengths and examples.
Master Gas Laws
Memorize and understand Boyle’s Law, Charles’s Law, Avogadro’s Law, and the Ideal Gas Equation. Practice numerical problems using PV = nRT.
Compare States of Matter
Make a table comparing solids, liquids, and gases in terms of shape, volume, compressibility, particle motion, and intermolecular forces.