(a) How does the atomic radius changes as you go
(i) from left to right in a period?
(ii) down a group in the periodic table?
(b) Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the Modern Periodic Table do these two elements belong? What type of bond will be formed between them and why?
(a) (i) Atomic radius decreases from left to right in a period because effective nuclear charge increases from left to right in a period. Due to this effective nuclear charge, the electronegativity increases and the attraction of nucleus on valence shell electrons also increases. So the size decreases.
(ii) Atomic radius increases down a group because number of shells increases.
(b) X12- 2, 8, 2
Y16- 2, 8, 6
These two elements belong to 3 period because period of an atom in periodic table is equal to the number of shells present in that atom.
These two elements will form ionic bond because X has two valence electrons so it will completely lose these two electrons to acquire noble gas electronic configuration and Y has six valence electrons and it has more electronegativity so it will gain two electrons to complete its octet. So X will completely give its two electrons to Y and ionic bond will form.