1kg of Aluminum contains many more atoms than 1kg of lead. Also, as you add energy some of it goes to increasing the average translational kinetic energy per atom, but some may go to increase the potential energy associated with the thermal motion. These potential energies are not the same for all substances. Thermal Expansion Most, but not all, materials expand when their temperature increases and shrink as their temperature decreases. Solids and liquids usually expand slowly with an increase in temperature.
Gasses tend to expand much more rapidly with temperature changes.
An exception to this is water.