ICSE Class 9 Answered

(i) The atom which changes into the cation (+ve ion) should have 1, 2 or 3 valency electrons while the other atom which changes into the anion (-ve ion) should have 5, 6 or 7 electrons in the valency shell.

(ii) A high difference of electro negativity (about 2) between the combining two atoms is necessary for the formation of an electrovalent bond. Hence, the electrovalent bond is not possible between the similar atoms.

(iii) There must be overall decrease in energy which means that the energy must be released. For this purpose an atom should have low value of Ionisation potential and the other atom should have high value of electron affinity.

(iv) The quantity of energy released when free ions combine together to form one mole of a crystal is called lattice energy (U). Higher the lattice energy, the greater will be the case of the forming an ionic compound.