Question #7b0f6

Phosphorus, #"P"#, is a main-group element, which means that you can find the number of non-bonding electrons in a phosphorus atom by looking at two things

• the atomic number of the element #-># this tells you the total number of electrons present in a neutral phosphorus atom.

• the group in which phosphorus is located in the periodic table #-># for main-group elements, the group number tells you the number of bonding electrons present in a neutral atom

The idea is that an atom's electrons can basically be split into two groups bonding and non-bonding.

Bonding electrons, also known as valence electrons, are the electrons located in the outermost shell of the atom. These are the electrons used for chemical reactions.

On the other hand, non-bonding electrons, also known as core electrons, are located in the inner shells of the atom and are not used for chemical reactions.

You can thus say that

#color(blue)(|bar(ul(color(white)(a/a)"total no. of e"^(-) = "no. of bonding e"^(-) + "no. of non-bonding e"^(-)color(white)(a/a)|)))#

So a, neutral atom has equal numbers of protons in the nucleus and electrons surrounding the nucleus. As you know, the number of protons present in the nucleus is given by the atomic number.

Grab a periodic table and look for phosphorus. You'll find it in period 3, group 15. Its atomic number is equal to #15#.

This means that a neutral phosphorus atom has a total of #15# electrons surrounding the nucleus.

Since it's located in period 15, you know that phosphorus has a total of #5# valence electrons. Remember, for main-group elements

#color(blue)(|bar(ul(color(white)(a/a)"group number" = "no. of valence e"^(-)color(white)(a/a)|)))#

So, phosphorus has #15# electrons, out of which #5# are bonding electrons. This means that it has

#"no. of non-bonding e"^(-) = "15 e"^(-) - "5 e"^(-) = color(green)(|bar(ul(color(white)(a/a)color(black)("10 e"^(-))color(white)(a/a)|)))#

Here's how an atomic structure diagram would look for a neutral phosphorus atom.

The valence electrons, shown here in purple, are located on the outermost energy shell. The non-bonding electrons, shown here in yellow, are located on the two inner shells.