Question

In the periodic table from left to right in a period, the atomic volume

• A. decreases
• B. increases
• C. remains same
• D. first decrease then increases

Answer 1

The Correct Option is D

The question addresses the trend of atomic volume across a period in the periodic table. Atomic volume is defined as the volume occupied by one mole of atoms of an element. As we move across a period from left to right, several factors influence the atomic volume:

• Effective Nuclear Charge: As we go from left to right in a period, the nuclear charge increases because of the addition of protons in the nucleus. This causes a greater attraction between the nucleus and the electrons, pulling the electrons closer, which generally decreases the atomic radius.
• Screening Effect: Although additional electrons are added to the same shell, the screening effect (or shielding effect) caused by the inner electrons does not increase significantly. Thus, the effective nuclear charge increases, leading to a decrease in atomic size initially.

Based on these factors, here's what happens to the atomic volume across a period:

• At the beginning of the period, as you move from one element to the next, the electrons are added to the same shell, while the nuclear charge increases. This pulls the electrons closer to the nucleus, reducing the size of the atom, and hence the atomic volume decreases.
• As we continue moving across the period, after the midpoint, the nature of bonding changes (atoms closer to achieving a full outer shell), influencing atomic interactions and volume. Due to increased electron repulsion in the outer orbitals and the start of filling of p-electrons, atomic volume starts increasing.

Thus, the atomic volume first decreases then increases across a period. This trend is because initially, the increased effective nuclear charge pulls atoms closer, reducing volume, but later electron-electron repulsion and other factors increase atomic volume.

Hence, the correct answer is: first decrease then increases.