# Question 452bf

Jun 6, 2017

Calcium cations and bromide anions.

#### Explanation:

I'm not sure what you mean by "types of ions", so I'll just show you what two ions are needed in order to have one formula unit of calcium bromide.

Ionic compounds consist of two ions--a positively charged ion called a cation and a negatively charged ion called an anion.

When we write the chemical formula for an ionic compound, we use subscripts to show how many cations and anions are present in one formula unit of the compound.

It's important to keep in mind that we do not add subscripts of $1$. This implies that if a chemical element is written without an added subscript, then that subscript is equal to $1$.

In this case, you know that calcium bromide is

${\text{CaBr}}_{\textcolor{red}{2}}$

This tells you that one formula unit of calcium bromide contains

• one calcium cation, 1 xx "Ca"^(?+)
• two bromide anions, color(red)(2) xx "Br"^(?-)

Now, you can find the two charges by looking at the location of the two elements in the Periodic Table.

Calcium is located in group 2, which implies that it loses $2$ electrons to form $2 +$ cations. On the other hand, bromine is located in group 17, which implies that it accepts $1$ electron to form $1 -$ anions.

You can thus say that one formula of calcium bromide consists of

• one calcium cation, $1 \times {\text{Ca}}^{2 +}$
• two bromide anions, $\textcolor{red}{2} \times {\text{Br}}^{-}$

In other words, $1$ calcium cation combines with $\textcolor{red}{2}$ bromide anions to form calcium bromide.

["Ca"]^(2+) + color(red)(2) * ["Br"]^(-) -> "CaBr"_ color(red)(2)#