Question

Which are the smallest and largest atoms?

Answer 1

Hint: We already know that the size of the atom can be measured through the atomic radius of the atom. If the atomic radius is greater then, its atomic size will also be larger and if the atomic radius is small and the atomic size will also be small.

Complete answer:
We can determine the largest and smallest atom only by looking at the atomic radius of the atom. Also, we know that atomic size depends upon the two main factors. The first one is the nuclear charge of an atom and another factor is the shielding effect by the other atom.
According to the modern periodic table, the atomic size of the atom decreases across the period i.e. when we go from left to right in the periodic table. Also, atomic size of the atom increases down the group i.e. when we go from top to bottom in the periodic table.
So, we can conclude that the element francium with the atomic number $$87$$ is the largest element. It is the last element present in group I whereas the element helium with the atomic number $$2$$ is the smallest number. It is the last element across the period I.
Therefore, the smallest atom is helium and the largest atom is francium.

Note:
It must be noted that new orbitals are added when we go down the group which increases the size of the atom. Also, when we go across the period, new protons are being added to the nucleus which increases the effective nuclear charge. Thus, it results in the decrease in the size of the atom.