Question

practice:write the electron configuration of the following:
•he (z = 2)
•o (z = 8)
•al (z = 13)
•ar (z = 18)
•ga (z = 31)

Explanation:

Step1: Recall electron - filling rules

Electrons fill orbitals in order of increasing energy (1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p etc.), with a maximum of 2 electrons in an s - orbital, 6 in a p - orbital, 10 in a d - orbital and 14 in an f - orbital.

Step2: Determine electron configuration for He

He has 2 electrons. They fill the 1s orbital. So the electron configuration is $1s^{2}$.

Step3: Determine electron configuration for O

O has 8 electrons. 2 fill the 1s orbital, 2 fill the 2s orbital, and 4 fill the 2p orbital. So the electron configuration is $1s^{2}2s^{2}2p^{4}$.

Step4: Determine electron configuration for Al

Al has 13 electrons. 2 fill the 1s orbital, 2 fill the 2s orbital, 6 fill the 2p orbital, 2 fill the 3s orbital, and 1 fills the 3p orbital. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$.

Step5: Determine electron configuration for Ar

Ar has 18 electrons. 2 fill the 1s orbital, 2 fill the 2s orbital, 6 fill the 2p orbital, 2 fill the 3s orbital, 6 fill the 3p orbital. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$.

Step6: Determine electron configuration for Ga

Ga has 31 electrons. 2 fill the 1s orbital, 2 fill the 2s orbital, 6 fill the 2p orbital, 2 fill the 3s orbital, 6 fill the 3p orbital, 2 fill the 4s orbital, 10 fill the 3d orbital, and 1 fills the 4p orbital. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{1}$.

Answer:

He: $1s^{2}$
O: $1s^{2}2s^{2}2p^{4}$
Al: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$
Ar: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$
Ga: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{1}$