Question

which of the following elements has the following complete electron configuration? 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
magnesium
calcium
argon
potassium
how many valence electrons would be shown in the lewis dot diagram for sodium?
6
11
1
4

Explanation:

1. For the first question, count the total number of electrons from the electron - configuration. The sum of electrons in \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) is \(2 + 2+6 + 2+6 + 2=20\). Calcium has an atomic number of 20, so it has 20 electrons.
2. For the second question, sodium has an atomic number of 11 and its electron - configuration is \(1s^{2}2s^{2}2p^{6}3s^{1}\). The valence electrons are the electrons in the outermost shell. Here, the outermost shell is the 3rd shell with 1 electron.

Answer:

1. B. Calcium
2. C. 1