JAMB - Chemistry (1989 - No. 10)

How many valence electrons are contained in the element represented \(^{31}\) \(_{15}\)P?
3
5
15
31

Explanation

The element is Phosphorus in group 5 with valencies of 3 and 5.

The electronic configuration of phosphorus is 2,8,5. Hence it has two valencies of +5 and -3. Since we do have 3 and 5 in the options provided, the valency of 5 is a better option since it has positive while 3 has a negative value.

The electron configuration of phosphorus (atomic number 15) is 1s² 2s² 2p⁶ 3s² 3p³. Valence electrons are those in the outermost shell, which in phosphorus's case are the 3s² and 3p³ electrons, totaling 5. 

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