Question

Which statement is correct?

A. Atomic radius decreases down group 17.
B. First ionization energy decreases down group 1.
C. Atomic radius increases across period 3 from Na to Cl.
D. First ionization energy decreases across period 3 from Na to Cl.

Answer 1

The correct statement is: D. First ionization energy decreases across period 3 from Na to Cl.

Step-by-step explanation:

The correct statement is: D. First ionization energy decreases across period 3 from Na to Cl.

Ionization energy is the energy required to remove an electron from an atom. In general, ionization energy increases across a period from left to right because the effective nuclear charge increases, making it harder to remove an electron. However, there are some exceptions to this trend.

In Period 3 of the periodic table, the first ionization energy decreases from sodium (Na) to chlorine (Cl). This is because, as you move from left to right across a period, the atomic radius decreases and the effective nuclear charge increases, making it more difficult to remove an electron. However, chlorine (Cl) has a higher atomic number than sodium (Na), so the additional shielding from the filled 3p sublevel of chlorine outweighs the increased effective nuclear charge, resulting in a lower first ionization energy compared to sodium.