A. B. and C are three elements with atomic number 6, 11 and 17 respectively.

i. Which of these cannot firm ionic bond? Why?

ii. Which of these cannot form covalent bond? Why?

iii. Which of these can form ionic as well as covalent bonds?

we know that

A is Carbon – ₆C¹²

B is Sodium – ₁₁Na²³

C is Chlorine – ₁₇Cl³⁵

(i) The configuration of carbon is 1s²2s²2p². It has exactly 4 electrons

in its outermost shell. So, it neither loses nor gains electrons to obtain octet. Rather it shares electrons with other atoms and gets stable by obtaining octet structure. So, it forms covalent compounds but not ionic compounds.

(ii) The configuration of sodium is 1s²2s²2p⁶3s¹. So, to obtain octet

and become stable, it can easily lose an electron which is 3s¹. Therefore, sodium forms ionic compounds.

(iii) The Chlorine (₁₇Cl³⁵) configuration is 1s²2s²2p⁶3s²3p⁵. So, it can

easily gain an electron to obtain octet , thereby forming ionic compounds. But it can also share electrons and form covalent compounds like in the case of HCl. So, chlorine forms both ionic and covalent compounds.