Screening by the valence electrons in atoms is _ .
A) more efficient than that by core electrons
B) less efficient than that by core electrons
C) responsible for a general increase in atomic radius going across a period
D) essentially identical to that by core electrons
E) both more efficient than that by core electrons and responsible for a general increase in atomic radius going across a period

Question

Quizplus · Accepted Answer

Screening by the valence electrons in atoms is less efficient than that by core electrons. Core electrons are closer to the nucleus and shield the valence electrons from the positive charge of the nucleus more effectively. This is why the atomic radius decreases going across a period, as the number of valence electrons is the same but the number of protons in the nucleus increases, making the attraction to the nucleus stronger.

Screening by the Valence Electrons in Atoms Is _