# Writing Ionic Formulas: Practice Problems

We’ll do a few more examples of how to write these

### ionic

compounds. We’ll go a lot faster. Okay, Calcium Fluoride, Calcium is here, Fluorine or Fluoride is here, metal and nonmetal, we want to talk about charges. So Calcium is in this column which makes it Ca two-plus (Ca2+) Fluorine-- fluoride is in this column so it's going to be one minus (F-). How do we balance these out? We got 2 plus (2+) here so I want to add another Fluorine so I have a total of 2 minus (2- ) to balance out the
2+. One atom of Calcium is balanced out by two atoms of Fluoride or Fluorine so I'm going to write CAF2. Alright, Magnesium Oxide. Go back to the periodic table, Magnesium here, Oxide here, metal and non-metal, so it's

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, so its charges are important. So Magnesium two-plus (Mg2+), Oxide, the word for oxygen when it has a charge, O two-minus (O2-). How are we going to balance out the charges? Oh! They are already balanced out. I have 2+ here and 2- here so we don't have to add
more of either one of the atoms so I can write out MgO. Remember, don’t write Mg1O1, without a number here it just means you have 1 atom. So that's Magnesium Oxide (MgO). And finally, Strontium Phosphide. Strontium (Sr) is right here, it's a metal. And Phosphide is what we call Phosphorus when it has a charge so it's a nonmetal. Metal and nonmetal. Charges are important so Strontium is in this column which means that it's Sr two-plus (Sr2+). Phosphide, Phosphorus is in this
column which means that it has a charge of three minus (P3-). This is like one of the examples we did previously, here's how we do it. We add another Phosphide so we have a total negative charge of six minus (6- ). To balance out the 6- charge, I’m going to add more Strontium which have two-plus (2+) each so Sr2+, now I have four plus (4+), now I add another Sr2+ and now I have a total of six plus (6+). Six plus (6+) balances out the six minus (6- ). Now I’m going to write the chemical
formula to show how many of each atom I need to balance of charges, I’m going to say Sr3P2, okay? So that's how we write

for these

### ionic

compounds. There's one thing that I want to say. Sometimes these

that you're

## writing

are referred to as

of binary

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compounds. Well know you know why they are

### ionic

because we have a metal and a non-metal and everything that we wrote. So that makes it

### ionic

means two. In every one of these

#### formulas

that we wrote have only two types of atoms. Sodium Chloride, Magnesium Oxide, Aluminum Oxygen, Lithium Oxygen and so forth. We might have more than two actual atoms and something like Li2O3 but there are only two types of atoms, two elements in each of these. So that’s why we call them binary. If this is all good for you, go ahead and move on with the videos. You’ll probably want to check out the videos on

## writing

the

#### formulas

for compounds that have
transitional metals and then

## writing

#### formulas

for compounds that have polyatomic ions and you can just keep moving ahead with naming these compounds.