Show that F forms ionic bond with Na but it forms covalent bond with H . (The atomic numbers of H , F and Na are 1 , 9 , and 11 respectively).

An ionic bond is formed between atoms when one atom transfers its electrons from itself to its neighbouring atom. Here, Sodium having one valence electron transfers it to Fluorine atom having seven valence electrons and thus an ionic bond is formed between them whereas HF is a polar covalent compound as Fluorine is more electronegative than hydrogen. Both fluorine and hydrogen are non-metals. Fluorine has seven valence electrons and hydrogen has one valence electron, therefore, they share electrons to form a covalent bond.

By giving example of an Ionic compound show that its ions do not obey the octet rule.

Lithium fluoride is an ionic compound whose ions does not obey octet rule. Lithium has one valence electron and fluorine has seven valence electrons. Lithium transfers it one valence electron to fluorine and thus becomes electron deficient.

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.