本题目来源于试卷: Classification of Matter A.1 Periodic Table Elements Classification，类别为 IB化学
[单选题]
Which statement regardingw* ( sef-d6h5pbdqk q9 the first ioq3j+ jibe, x,i,0xk /xzmo7 mbnization energies (A(g)→$A^{+}$(g)+e-) of the period 2 correctly supports the evidence of sublevels in atoms?
I.Each period 2 element shows an increase in ionization energies across the table from left to right
II.Boron has a lower first ionization energy than beryllium because boron has an electron in the 2p sublevel
III.Oxygen has a lower first ionization energy than nitrogen due to oxygen’s greater effective nuclear charge
A. $I$ only
B. $II$ only
C. $I$ and $II$ only
D. $II$ and $III$ only
参考答案: B
本题详细解析:
Explanation: The general trend for ionization energy across a period is to increase, but small decreases are observed between Be and B and again between N and O, making statement I incorrect. These small decreases are due to the increased stability of the full and half full sublevels. The 2s orbital in BeBe is full, making it more difficult to remove an electron from BeBe than BB, so BB has a lower ionization energy. The 2p sublevel of NN is half full, making it more difficult to remove an electron from N than O. The observed decrease is due to the half full sublevel of N, not the effective nuclear charge of O (O does have a greater effective nuclear charge, but this alone would cause an increase the ionization energy).
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