# Question #81233

##### 1 Answer

Here's what I got.

#### Explanation:

As you know, a *neutral atom* has **equal numbers** of protons inside the nucleus and of electrons surrounding the nucleus.

This implies that your element, which has an **atomic number** equal to **protons** inside the nucleus, must have a total of **electrons** surrounding the nucleus.

Now, each **period** of the Periodic Table corresponds to an **energy shell** in which these electrons can reside. The maximum number of electrons that each shell can hold is given by

#color(blue)(ul(color(black)("no. of e"^(-) = 2n^2)))#

Here *principal quantum number*.

So all you have to do here is to figure out how many **full shells** are present in your atom. You start with **electrons** to distribute, so you have

#n = 1 -> "no. of e"^(-) = 2 * 1^2 = 2# The

first energy shellcan hold a maximum of#2# electrons, so subtract this from#13# to get#11# electrons left to distribute.

#n = 2 -> "no. of e"^(-) = 2 * 2^2 = 8# The

second energy shellcan hold a maximum of#8# electrons, so subtract this from#11# to get#3# electrons left to distribute.

#n = 3 -> "no. of e"^(-) = 2 * 3^2 = 18# The

third energy shellcan hold a maximum of#18# 8electrons*., but since you only haveelectrons#3# left to distribute in this energy shell, you can say that theseelectrons#3# will be the atom'svalence electrons

You can say that because the *valence electrons* are located in the **outermost energy shell**, which in your case is the third energy shell.

You can thus say that your atom has **valence electrons** located in the **third energy shell**.