普化問題 結構

The answer is : (e) Two of the above could be X.

In XCl5⁻, the central atom is X andthe shape of the five X-Cl bonds is square pyramidal. It can be deduced thatthe central atom X has 5 bond pairs and 1 lone pair of electrons, and the 6 electronpairs are octagonal in shape. To state the shape of the XCl5⁻, the lone pair ofelectrons is neglected, and thus it becomes square pyramidal.

In XCl5⁻, the central atom has 5bond pairs and 1 lone pair of electrons. Considering there is an extra electronin XCl5⁻, X atom in free state has6 valence electrons. All of O, S and P would have 6 valence electrons. However,O cannot expands its octet. Therefore, Xcan be S or P.

2013-11-26 00:07:01 補充：
Alternative explanation.

(A) incorrect
O cannot form OCl5⁻. This is because O cannot expand its octet, but X has 10 electrons in its outermost shell.

2013-11-26 00:08:48 補充：
(B) incorrect
In XeCl5⁻, the central atom Xe has 5 bond pairs and 2 lone pairs of electrons. The 7 electrons pairs are pentagonal bipyramidal in shape, and thus the 5 bond pairs would NOT form a square pyramidal.
(Actually, XeCl5⁻ does NOT exist. Xe can form covalent bonds with F and O, but NOT Cl.)

2013-11-26 00:09:19 補充：
(C) correct
In SCl5⁻, the central atom S has 5 bond pairs and 1 lone pair of electrons. The 6 electrons pairs are octagonal in shape, and thus the 5 bond pairs form a square pyramidal.

2013-11-26 00:09:57 補充：
(D) correct
In PCl5⁻, the central atom P has 5 bond pairs and 1 lone pair of electrons. The 6 electrons pairs are octagonal in shape, and thus the 5 bond pairs form a square pyramid.

2013-11-26 17:30:22 補充：
Sorry, the answer is (c) S only.

(d) is incorrect.
In PCl5⁻, the central atom P has 5 bond pairs and 1 unpaired electron. This is a very unstable structure and thus PCl5⁻ does NOT exist.

2013-11-26 17:31:37 補充：
Sorry again, I mixed up As and P. It is actually P, but in my mind it is As instead.