Question

module 4: electrons in atoms test - 11/14/2025
the element sodium is one of the elements that compose the earths crust. what is the electron configuration for sodium, na
( 1 s ^ { 2 } 2 s ^ { 2 } 2 p ^ { 6 } 3 s ^ { 1 } )
( 1 s ^ { 2 } 2 s ^ { 2 } 2 p ^ { 6 } 3 s ^ { 1 } 4 s )
( 1 s ^ { 2 } 2 s ^ { 2 } 3 s ^ { 1 } 2 p ^ { 6 } )
( 1 s ^ { 2 } 2 p ^ { 6 } 3 s ^ { 1 } 3 p ^ { 2 } )

Explanation:

Step1: Determine the atomic number of sodium

The atomic number of sodium ($Na$) is $11$. This means a neutral sodium atom has $11$ electrons.

Step2: Fill the electron orbitals according to the Aufbau principle

• The $1s$ orbital can hold a maximum of $2$ electrons: $1s^{2}$.
• The $2s$ orbital can hold a maximum of $2$ electrons: $2s^{2}$.
• The $2p$ orbital can hold a maximum of $6$ electrons: $2p^{6}$.
• After filling $1s$, $2s$, and $2p$, we have used $2 + 2+6 = 10$ electrons. The remaining $1$ electron goes into the $3s$ orbital: $3s^{1}$.

Answer:

$1s^{2}2s^{2}2p^{6}3s^{1}$ (the first option)