Question

match the letter of the following electron configurations with the number of valence electrons. note: valence electrons for transition metals are omitted due to the presence of additional d subshell electrons.
electron configurations|number of valence electrons:
a. 1s² 2s² 2p⁶ 3s² 3p⁵
b. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰5p³
c. 1s² 2s² 2p⁶ 3s² 3p⁴
d. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s²
e. 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶
electron configurations:|number of valence electrons:
a. choose
b. choose
c. choose
d. choose
e. choose

Explanation:

Step1: Recall valence - electron rule

Valence electrons are the electrons in the outermost shell. For the given electron - configurations, we only consider the electrons in the highest - numbered shell.

Step2: Analyze configuration A

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$, the outermost shell is the third shell ($n = 3$). The number of electrons in the $3s$ and $3p$ sub - shells is $2 + 5=7$.

Step3: Analyze configuration B

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{3}$, the outermost shell is the fifth shell ($n = 5$). The number of electrons in the $5s$ and $5p$ sub - shells is $2+3 = 5$.

Step4: Analyze configuration C

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}$, the outermost shell is the third shell ($n = 3$). The number of electrons in the $3s$ and $3p$ sub - shells is $2 + 4=6$.

Step5: Analyze configuration D

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}$, the outermost shell is the fifth shell ($n = 5$). The number of electrons in the $5s$ sub - shell is $2$.

Step6: Analyze configuration E

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$, the outermost shell is the fourth shell ($n = 4$). The number of electrons in the $4s$ and $4p$ sub - shells is $2+6 = 8$.

Answer:

A. 7
B. 5
C. 6
D. 2
E. 8