Question

What does a high melting point temperature indicate about a substance?

Answer 1

Melting, or the change of physical states, is the change of distance between particles. In solid state, particles are closely packed together. Energy is required to separate them in order to make it become liquid or even gas.
When a substance has a high melting point, it means the intermolecular forces or the chemical bonds are strong and the particles are easily attracted to each other. Therefore, more energy is needed to overcome these forces. A higher temperature could provide such energy.
Elements are combined together by different kinds of bonds. Ionic bonds and metallic bonds are considered to be strong. Ionic compounds (eg. NaCl) and metals tend to have a high melting point. In covalent compounds, molecules are held by weak van der Waals’ force. Thus, covalent compounds (eg. most gases, like CO2) have a low melting point.
Yet, water molecules, which are covalent compounds, have a higher melting point than others. It is because water molecules are polar, which allows hydrogen bonds to form among molecules, keeping them close together. More energy is required to melt ice or boil water than normal covalent compounds.