18. what is the electron configuration for each of the following elements? a. he b. si c. as d. kr 19. write…

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 of He

Helium has 2 electrons. It fills the 1s orbital. So the electron configuration is $1s^{2}$.

Step3: Determine electron configuration of Si

Silicon has 14 electrons. Filling order: 1s takes 2 electrons, 2s takes 2 electrons, 2p takes 6 electrons, and 3s takes 2 electrons, and 3p takes 2 electrons. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}$.

Step4: Determine electron configuration of As

Arsenic has 33 electrons. Filling order: After filling up to 3p (18 electrons), 4s takes 2 electrons, 3d takes 10 electrons, and 4p takes 3 electrons. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$.

Step5: Determine electron configuration of Kr

Krypton has 36 electrons. Filling order: After filling up to 4p (33 electrons for As), the remaining 3 electrons fill the 4p orbital completely. So the electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$.

Answer:

a. $1s^{2}$ b. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{2}$ c. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{3}$ d. $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$