Question

The atom of smallest atomic radius among the following is
A.Na
B.K
C.Br
D.Li

Answer 1

Hint: We must know that the atomic radius decreases gradually from left to right across the period in the periodic table. And this is because all atoms add electrons to the same shell within the periods.

Complete step by step solution:
Group 1A of the periodic table are the alkali metals and from the given options sodium ($$Na$$), potassium ($$K$$) and Lithium ($$Li$$) belongs to alkali earth metals, whereas bromine ($$Br$$) belongs to halogen family.
Variations in atomic radii are observed due to the effective nuclear charge that holds the valence electrons close to the nucleus. This is due to trends in the periodic table. Atomic radius decreases as we go across a period from left to right whereas the trend of atomic radii is seen decreasing as we move up a group from bottom to top.
Electrons are added to the same energy level, as we move across a period and at the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus ultimately generates a higher effective nuclear charge.
Or we can say that there is a stronger force of attraction that pulls the electrons closer to the nucleus which gives a smaller atomic radius.
Moreover, the radius of alkali metals is metallic radius, whereas the radius of halogens is covalent radius. You always remember that metallic radius is always higher than that of the covalent radius.
Thus, from the given options, we can conclude that Bromine ($$Br$$ ) has the smallest atomic radius as it belongs to halogens and so have covalent radius.

Note: We must know that out of all the elements present and known so far, Helium ($He$) has the smallest atomic radius. This is because helium has two protons on its nucleus. Therefore, it shows more attraction to its electrons. That’s why helium has a smaller atomic radius.