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 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 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 formulas for these
ionic compounds. There's one thing that I want to say. Sometimes these formulas that you're writing
are referred to as formulas of binary ionic 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, metal and nonmetal. What about this binary part? Binary 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.