Question

Which of the following has the largest radius?
A. $ 1{s^2},2{s^2},2{p^6},3{s^2} $
B. $ 1{s^2},2{s^2},2{p^6},3{s^2},3{p^1} $
C. $ 1{s^2},2{s^2},2{p^6},3{s^2},3{p^3} $
D. $ 1{s^2},2{s^2},2{p^6},3{s^2},3{p^5} $

Answer 1

Hint: Atomic radius is the distance from the atom's nucleus to the outer edge of the electron cloud. In general, atomic radius decreases across a period and increases down a group. Across a period, effective nuclear charge increases as electron shielding remains constant. The value of atomic radii depends on the type of chemical bond in which the atoms are involved.

Complete Step By Step Answer:
Atomic size gradually decreases from left to right across a period of elements. This is because, within a period or family of elements, all electrons are added to the same shell. However, at the same time, protons are being added to the nucleus, making it more positively charged. Down a group, atomic radius increases.
The size of an atom or ion depends on the size of the nucleus and the number of electrons. Generally atoms with higher numbers of electrons have larger radii than those with smaller numbers of electrons. Thus ions will have radii different from the atoms because ions will have either gained or lost electrons.
Atomic size increases with the increase in the number of electron shells. Thus atomic radius is directly proportional to the number of electron shells.
Therefore, $ 1{s^2},2{s^2},2{p^6},3{s^2} $ has the largest radius.
So, the correct answer is (A) $ 1{s^2},2{s^2},2{p^6},3{s^2} $ .

Note:
The anionic radius is difficult to define because an anion has an additional electron, which increases the size of the electron cloud and may make the ionic radius larger than the atomic radius. Values for ionic radius are difficult to obtain and tend to depend on the method used to measure the size of the ion.