Question

(a) What are the electron configurations of the ground states of lithium \((Z=3),\) sodium \((Z=11),\) and potassium \((Z=19) ?\) (b) Why are these elements placed in the same column of the periodic table?

Short answer

Answer: Lithium, sodium, and potassium are placed in the same column of the periodic table because they have the same outer electron configuration, with one electron in their outermost s-orbital. This results in similar chemical properties among these elements, also known as alkali metals.

Step-by-step solution

Determine the electron configuration of Lithium (Z=3)

To find the electron configuration of Lithium, we first look at its atomic number (Z=3) which tells us that it has 3 electrons in the ground state. The electron configuration for Lithium will follow the order in which the atomic orbitals fill, starting with the lowest energy orbital (1s) and going in ascending order (2s, 2p, 3s, 3p, etc.). The electron configuration for Lithium (Z=3) is: \(1s^2 2s^1\)

Determine the electron configuration of Sodium (Z=11)

Like we did for lithium, we look at the atomic number of Sodium (Z=11) which tells us that it has 11 electrons in the ground state. The electron configuration following the same order as before, will be: The electron configuration for Sodium (Z=11) is: \(1s^2 2s^2 2p^6 3s^1\)

Determine the electron configuration of Potassium (Z=19)

Lastly, we look at the atomic number of Potassium (Z=19) which tells us that it has 19 electrons in the ground state. The electron configuration following the same order will be: The electron configuration for Potassium (Z=19) is: \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1\)

Compare electron configurations and relate to their position in the periodic table

When comparing the electron configurations of lithium (\(1s^2 2s^1\)), sodium (\(1s^2 2s^2 2p^6 3s^1\)), and potassium (\(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1\)), we can observe that they all have one electron in their outermost s-orbital with electron configurations that differ only in the number of filled inner orbitals. These elements are placed in the same column of the periodic table (alkali metals) because they have the same outer electron configuration, which results in similar chemical properties.