# What is the energy level and sublevel in which a neutral sodium atom's valence electron is found?

Oct 28, 2015

The valence electron of a neutral sodium atom in its ground state is in the $\text{3s}$ sublevel.

#### Explanation:

Sodium has an atomic number of 11, which is the number of protons in the nuclei of its atoms. A neutral sodium atom also has 11 electrons.

The electron configuration of a neutral sodium atom is $\text{1s"^2"2s"^2"2p"^6"3s"^1}$.

For the atoms of the representative elements (all elements except for the inner and outer transition metals), their valence electrons are in their outermost (highest energy) $\text{s}$ and $\text{p}$ sublevels.

Therefore, the valence electron of a neutral sodium atom in its ground state is in its $\text{3s}$ sublevel, in which $3$ represents the principal energy level, and $\text{s}$ represents the sublevel.

Oct 28, 2015

Sodium has one electron on the 3s sublevel.

#### Explanation:

The question wants you to determine the energy level and sublevel on which sodium's valence electron can be found.

Notice that you are given sodium's atomic number, which tells you how many protons it has in its nucleus,

You know that a neutral sodium atom must have equal numbers of protons in the nucleus and electrons surrounding the nucleus.

This means that sodium has a total of $11$ electrons surrounding its nucleus. Its electron configuration will thus be

$\text{Na: } 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} \textcolor{red}{3} {s}^{1}$

Now, notice that sodium's electron configuration shows

• 2 electrons in the 1s sublevel
• 2 electrons in the 2s sublevel
• 6 electrons in the 2p sublevel
• 1 electron in the 3s sublevel

Therefore, sodium has one electron on its 3s sublevel, which is a part of the third energy level.