The elements of the third period of the Periodic Table are given below:

(a) Which atom is bigger, Na or Mg? Why?
(b) Identify the most (i) metallic and (ii) non-metallic element in Period 3.
(c) Which is more non-metallic, S or Cl?
(d) Which has higher atomic mass, Al or Cl?

Explanation

(a) Na is bigger than Mg because on moving from left to right in a period, the atomic number of elements increases which means that the number of protons and electrons in the atom increases. ( The extra electrons being added to the same shell).
(b) (i) Most metallic element is Na. Most non-metallic element is Cl,
Because on moving from left to right in a period the nuclear charge increase thus the vlence electrons are pulled in more strongly by the nucleus and it becomes more and more difficult for the atoms to lose electrons so tendency of atoms to lose electrons (i.e., metallic character) decreases on moving from left to right in a period.
On the other hand, due to increased nuclear charge, it becomes easier for the atoms to gain electrons. So the tendency to gain electrons (i.e., non-metallic character) increase on moving from left to right left to right in a period.
(c) Cl is more non-metallic from S because on moving from left to right in a period, nuclear charge increase so the tendency to gain electrons increases (i.e., non-metallic character).
(d) Cl has higher atomic mass because on moving from left to right in a period, atomic number increase. Simultaneously, atomic mass increases.