Question

based on its position in the periodic table of the elements, how many valence electrons does phosphorus (atomic number 15) have?
o 3
o 5
o 8
o 15

Explanation:

Step1: Write electron - configuration

The electron - configuration of phosphorus (atomic number 15) is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}$.

Step2: Identify valence electrons

Valence electrons are in the outermost shell. For phosphorus, the outermost shell is the third shell ($n = 3$), and the number of electrons in the $3s$ and $3p$ sub - shells is $2 + 3=5$. So phosphorus has 5 valence electrons.

Answer:

B. 5