Question

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

Which atom is bigger, Na or Mg? Why?

Answer 1

Bigger atom among $Na$ and $Mg$:

• Magnesium's nuclear charge is higher than the Sodium nuclear charge. Thus Magnesium is smaller than Sodium by attracting electrons towards it by shrinking the size.
• On moving from $Na$ to $Cl$ in the third period, the atomic number increases, and thereby, the nuclear charge also increases.
• This leads to a greater attraction of the electrons towards the nucleus, leading to the shrinkage of the atom.
• Although the number of electrons also increases, each additional electron is placed within the same shell, thus all the electrons being equidistant from the nucleus.

$\mathbf{Na}$ is a bigger atom than $\mathbf{Mg}$ as it is placed on the farthest left of the period. $Mg$ has a greater nuclear charge than $Na$.