Which of the following statements about the effective nuclear charge, Z_eff, is correct? A)Z _eff increases with the size of the atom. B)Z _eff decreases across a period and increases down a group. C)Z _eff increases across a period and is relatively constant down a group. D)Z _effincreases as the value of the principal quantum number increases. E)Z _eff is greater for hydrogen than for any other element.

Question

Quizplus · Accepted Answer

The effective nuclear charge, Z_eff, is the net positive charge experienced by an electron in an atom. It takes into account the attractive force of the nucleus and the repulsive force of the electrons in the same electron shell. Across a period, the number of protons in the nucleus increases, which increases the attractive force on the electrons. At the same time, the number of electrons in the same shell also increases, which increases the repulsive force. As a result, the effective nuclear charge increases across a period. Down a group, the number of electron shells increases, which shields the outer electrons from the attractive force of the nucleus. As a result, the effective nuclear charge remains relatively constant down a group. Therefore, option C is correct: Z_eff increases across a period and is relatively constant down a group.

Which of the Following Statements About the Effective Nuclear Charge