Question

On moving from left to right in a period in the periodic table, the size of the atom.

• A. Increases
• B. Decreases
• C. Does not change appreciably
• D. First decreases and then increases

Answer 1

The correct option is B

Decreases

The explanation for correct answers:

Option (B) Decreases

• The distance from the nucleus to the valence shell of an atom is termed atomic size
• Atomic radius is coined as half the distance between adjacent atoms of the same element in a molecule.
• Atomic size depends upon the nuclear charge and the number of shells.
• If we consider the elements in the same period the number of shells remains the same, but the nuclear charge increases as we move across the period.
• On increasing the effective nuclear charge the valence electrons are attracted more towards the nucleus which in turn increases the inward nuclear pull that makes the valence shell come closer to the nucleus and hence the size of the atom decreases as we move from the left to right in a period.
• As we move along the period, the atomic number of the atoms increases but the number of shells will always remain the same, that is electronic attraction increases and hence reducing the size.
• The atomic size of atoms decreases as the atomic number (i.e., the number of protons and electrons) increases but the number of shells remains the same on moving from left to right in a period.
• Therefore as the attractive forces between the nucleus and the outermost shell of electrons (called an effective nuclear charge) increase, atomic size decrease.
• Hence option (B) Decreases