Question

the trend towards smaller atomic radii as one moves to the right in a period is ______. answer: a faulty, as atomic radii in a period are nearly uniform in size. b because of electron pair repulsion causing the expansion of the orbitals. c wrong. atomic radii increase across a period left to right as the larger d and p orbitals are occupied after the s orbital. d due to the effective nuclear charge decreasing. e due to the effective nuclear charge increasing.

Explanation:

As one moves to the right in a period, the number of protons in the nucleus increases (increasing the positive charge of the nucleus). The electrons are added to the same shell (so the shielding effect remains relatively constant). The effective nuclear charge (the net positive charge experienced by the outermost electrons) increases. This stronger attraction of the nucleus for the electrons pulls the electrons closer, resulting in a smaller atomic radius.

• Option A is incorrect as atomic radii in a period are not nearly uniform.
• Option B is incorrect as electron - pair repulsion is not the reason for the trend of decreasing atomic radius across a period.
• Option C is incorrect as atomic radii decrease (not increase) across a period from left to right.
• Option D is incorrect as the effective nuclear charge increases (not decreases) across a period.

Answer:

E. due to the effective nuclear charge increasing.