# Question #5e7c5

Oct 20, 2017

$3 -$

#### Explanation:

The problem wants you to recognize the fact that the difference between the number of protons and the number of electrons gives you the net charge of an atom or ion.

$\textcolor{b l u e}{\underline{\textcolor{b l a c k}{\text{net charge" = "no. of protons " - " no. of electrons}}}}$

Now, the fact that you need to subtract the number of electrons from the number of protons will help with the sign of the net charge. In this regard, you can distinguish three cases:

• $\text{no. of protons " > " no. of electrons}$

In this case, you have

$\text{net charge} > 0$

This implies that an atom that has more protons inside its nucleus than electrons surrounding its nucleus will become a positively charged ion, or cation.

• $\text{no. of protons " < " no. of electrons}$

In this case, you have

$\text{net charge} < 0$

This implies that an atom that has more electrons surrounding its nucleus than protons inside its nucleus will become a negatively charged ion, or anion.

• $\text{no. of protons " = " no. of electrons}$

In this case, you have

$\text{net charge} = 0$

This implies that an atom that has equal numbers of protons inside the nucleus and of electrons surrounding the nucleus will not carry a net carry, i.e. it will be electrically neutral.

In your case, you know that this hypothetical ion has $58$ electrons and $55$ protons, which means that it has

$\text{net charge} = 55 - 58 = - 3$

This tells you that the ion carries a $3 -$ charge, which is consistent with the fact that it has $3$ more electrons than protons.