Question

Consider the atomic radius of the atoms in Period 2. Notice that the radius decreases from left to right accross the period, even though the number of valence electrons increases. Why doesn't atomic radius increase across a period? (Hint: consider effective nuclear charge.)

Answer 1

"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. The effect of increasing proton number is greater than that of the increasing electron number; therefore, there is a greater nuclear attraction. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The valence electrons are held closer towards the nucleus of the atom. As a result, the atomic radius decreases.

For going down a group, the number of outer electrons increase. Thus, the atom as a whole gets bigger since more energy levels exist.