Effect of change of temperature on matter: On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles.

As the motion of particles increases, particles move further apart. The attractive forces between particles get weaker. The spaces between them increase and the particles can slip past one another.

If we cool it down, it changes into a solid – ice. If we heat it up, it changes into a gas – steam. A particular material changes from being a solid to a liquid at a fixed temperature. This is its melting point.

When a substance is heated, it gains thermal energy. Therefore, its particles move faster and its temperature rises. When a substance is cooled, it loses thermal energy, which causes its particles to move more slowly and its temperature to drop.

When boiling occurs, the more energetic molecules change to a gas, spread out, and form bubbles. These rise to the surface and enter the atmosphere. In addition, gas molecules leaving the liquid remove thermal energy from the liquid. Therefore the temperature of the liquid remains constant during boiling.

When heated, air expands and increases in volume, density, and sometimes pressure if in a closed container. Sorry, but you can’t melt air. Firstly air is not solid, so you can’t melt it anyway.

The force of attraction between the molecules affects the melting point of a compound. Stronger intermolecular interactions result in higher melting points. Ionic compounds usually have high melting points because the electrostatic forces holding the ions (ion-ion interaction) are much stronger.

beryllium

Covalent crystals

The van der Waals forces are strongest in I2 imparting it the highest melting points and boiling point. At room temperature ,F2 and Cl2 are gases Br2 is liquids and I2 is a solid.

We know that Fluorine has the smallest size and is the most electronegative element. That means that it has the strongest bonding with the metal Na. So a lot of heat will be required to melt it, and hence, NaF has the maximum melting point.