Why does the outermost electron of boron experience a lower effective nuclear charge than that of carbon?

• A. Boron has fewer protons in its nucleus than carbon, resulting in a weaker attraction for the outermost electron.
• B. Boron has more electron shielding than carbon, which increases the effective nuclear charge.
• C. Boron and carbon have the same effective nuclear charge because they are in the same period.
• D. Carbon's outermost electron is in a higher energy level than boron's, reducing its effective nuclear charge.

Answer: (A)

Verified step by step guidance

1. Understand the concept of effective nuclear charge (Z_eff), which is the net positive charge experienced by an electron in an atom. It accounts for the actual nuclear charge (number of protons) minus the shielding effect caused by other electrons.
2. Recall that boron (B) has 5 protons and carbon (C) has 6 protons in their nuclei. The number of protons directly affects the nuclear charge attracting the electrons.
3. Recognize that both boron and carbon have their outermost electrons in the same principal energy level (the second shell), so the shielding effect from inner electrons is similar for both elements.
4. Since carbon has one more proton than boron, its nucleus exerts a stronger positive charge, pulling its outermost electron closer and increasing the effective nuclear charge experienced by that electron.
5. Conclude that the outermost electron of boron experiences a lower effective nuclear charge than that of carbon primarily because boron has fewer protons, resulting in a weaker attraction despite similar shielding.