Question

Atomic size across the period increases with increase in nuclear charge of element.
(A)- True
(B)- False

Answer 1

The outermost electrons in an element experience both attractive force (from the nucleus) and the repulsive force (from the electrons in the prior shells). These play an effective role in order to determine the size of the element in the periodic table.

Complete step by step answer:
Firstly, an atomic size of the elements is denoted with respect to its atomic radius. It is the distance from the centre of the nucleus to the outermost shell. Then, along the period it is seen that in the electronic configuration obtained using the Aufbau principle that, as the atomic number or the number of electrons increases, the electrons get added into the same shell as the adjacent element, which remains the same along the period.
Then, these electrons experience electrostatic attraction forces from the positively charged nucleus. This is known as the effective nuclear charge. It gets affected by the non-valence electrons that shield the outermost electrons from the nucleus. This is called the shielding effect. So, greater the shielding effect, more is the decrease in the effective nuclear charge experienced by the valence electrons.
But along the period, this shielding by electrons remains constant as the electrons get added. So, the effective nuclear charge increases, pulling the electron cloud closer to the nucleus. Hence, causing decrease in the atomic radius and thus, the atomic size.

Therefore, the statement that the atomic size across the period increases with increase in nuclear charge of element is option (B)- False.

Note: The decrease in the atomic size is only found across the period, but as the shell number increases, that is, down the group, the atomic size increases, because along with the attraction force, the valence electrons also face repulsion from the other electrons in prior shells. As this decreases the effective nuclear charge experienced by the valence electrons.