The answer is: the type of bonding among the particles.
For example, calcium oxide (CaO) has ionic bonds between calcium cations (Ca²⁺) and oxygen anions (O²⁻).
Because it has strong ionic bonds, it has high melting point (around 2600°C).
Ionic bond is the electrostatic attraction between oppositely charged ions (cations and anions).
Amount of energy required to change 1 gram of material from the solid to the liquid state at its melting point
