Writing Ionic Formulas: Practice Problems

We'll do some more examples of how to write these

ionic

compounds. We will go much faster. Well, calcium fluoride, calcium is here, fluorine or fluoride is here, metal and non-metal, we want to talk about charges. So calcium is in this column, which converts it to Ca two plus (Ca2+). Fluorine. Fluoride is in this column, so it will be one less (F-). How do we balance them? We have 2 more (2+) here, so I want to add another fluorine to have a total of 2 less (2-) to balance out the 2+. One calcium atom is balanced by two fluoride or fluorine atoms, so I'll write CAF2.

Okay, magnesium oxide. Let's go back to the periodic table, magnesium here, oxide here, metal and non-metal, so it's

ionic

, 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 the charges? Oh! They are already balanced. I have 2+ here and 2- here, so we don't have to add more of any of the atoms in order to write MgO. Remember, don't write Mg1O1, without a number here it just means you have 1 atom. That is magnesium oxide (MgO).

And finally, strontium phosphide. Strontium (Sr) is here, it is a metal. And phosphide is what we call phosphorus when it has a charge, so it is a non-metal. Metal and non-metal. Charges are important, so strontium is in this column, which means it is Sr two or more (Sr2+). Phosphide, phosphorus is in this column which means it has a charge of three minus (P3-). This is like one of the examples we did earlier, this is how we do it. We add another phosphide to have a total negative charge of six minus (6-). To balance the charge of 6, I'm going to add more strontium which has two more (2+) each, so Sr2+, now I have four more (4+), now I add another Sr2+ and now I have a total. of six more (6+).

Six plus (6+) balances the six minus (6-). Now I'm going to write the chemical formula to show how many atoms of each I need to balance the charges. I'm going to say Sr3P2, okay? This is how we write

formulas

for these ionic compounds. There is one thing I want to say. Sometimes these

formulas

you are

writing

are called formulas for binary ionic compounds. Well, you know why they are ionic because we have a metal and a non-metal and everything we write. That makes it ionic, metallic and non-metallic. What about this binary part? Binary means two. In each of these formulas that we write there are only two types of atoms.

Sodium chloride, magnesium oxide, aluminum oxygen, lithium oxygen, etc. We could have more than two real atoms and something like Li2O3, but there are only two types of atoms, two elements in each of them. That's why we call them binary. If all this sounds good to you, continue with the videos. You'll probably want to watch the videos on how to write formulas for compounds that have transition metals and then write formulas for compounds that have polyatomic ions and you can go ahead and name these compounds.