Explain why the melting point of sodium chloride is much greater than that of glucose.

Sodium chloride has a high melting point because the lattice is constructed from positive sodium ions and negative chloride ions. This ions attract each other with a strong electrostatic force. To break the bonds between the ions you need high temperature. The intermolecular forces glucose has are hydrogen bonding between the hydrogen and oxygen, dipole dipole between the negative end and positive end of the molecule and London dispersion forces which are weak forces and hence the melting point of sodium chloride is much greater than that of glucose.

Give one example each of a liquid and a solid covalent bond.

Covalent compounds are those in which the atoms are chemically linked together by the sharing of electrons. A covalent compound can exist in three states: solid, liquid, and gaseous. Silica, for example is a covalent molecule that occurs in a solid state. Water is also a covalent molecule that occurs as a liquid. The intermolecular forces of attraction between the molecules of covalent compounds are weak. They are brittle as a result, and can be readily broken down as a result.