In this video, we're going to talk about how to write the chemical formula of ionic compounds. So let's say if we have lithium chloride. How can we write the formula of this ionic compound? The first thing you want to do is write the charges of each ion.
Lithium has a plus one charge. All of the alkaline metals in group one have a positive one charge. an ion.
Chloride has a minus one charge. Now whenever the charges are the same, you could simply write the elements together. So therefore, lithium chloride is simply LiCl. You don't need any subscripts if the charges are the same. So let me give you another example of that.
Calcium sulfide. Calcium is an alkaline earth metal found in group 2A of the periodic table, so therefore it has a positive 2 charge. Sulfide has a minus 2 charge.
Because the charges are the same, you can simply write them together with no subscripts. So it's simply called Cas, calcium sulfide. Now let's look at another similar example.
Aluminum nitride. Aluminum has a positive 3 charge. Nitride has a negative 3 charge. Once again the charges are the same. So you could simply write it as Aln, aluminum nitride.
Let's work on this one. Magnesium Bromide. Magnesium, like calcium, is an alkaline earth metal found in group 2, and it has a plus 2 charge.
Bromide is a halogen that has a minus 1 charge. Now notice that this time, the charges are not the same. they're different so in this situation you want to exchange the charges with subscripts and you got to reverse them so the plus 2 which is the charge on magnesium will become the subscript for bro and the minus 1, which is the charge on bromine, will become the subscript of Mg.
So it's going to be Mg1Br2. The negative sign does not carry over. Now, if you have a 1, you don't need to write it.
So you could ignore the 1. So you could simplify and say this is MgBr2. So that's what you need to do whenever the charges are not the same. So let's look at another example. Sodium, sulfide.
Sodium has a positive 1 charge. Sulfide has a minus 2 charge. So using the same method, it's going to be Na2S1, but we don't have to write the 1, so it's going to be simply Na2S. Try these two problems. Aluminum fluoride.
And also, calcium phosphide. Aluminum is a metal found in group 3A, so it has a positive 3 charge. Fluoride is a halogen for minus 1 charge.
So using the same method, it's going to be Al1F3, or simply AlF3. So once you work on a few examples and get the hang of it, this process becomes a piece of cake. Calcium has a plus 2 charge.
Phosphorus, as an ion, has a minus 3 charge. So let's switch the charges with subscripts. So it's going to be Ca3P2. Here's another two examples that you can work on with polyatomic ions. So write the chemical formula of aluminum sulfate and also strontium phosphate.
Aluminum, as we mentioned before, has a positive 3 charge. Sulfate is SO4 with a negative 2 charge. So let's use the same crisscross method. So it's going to be Al2SO4 3. Now, if you have multiple polyatomic ions, you need to enclose it within a parenthesis.
So that's how you write the chemical formula of aluminum sulfate. Now, strontium is... Strontium is Sr.
It's an alkali earth metal with a positive 2 charge. Phosphate is PO4 with a negative 3 charge. So this is going to be called Sr3PO4 times 2. So that's the chemical formula of strontium phosphate.
Now let's incorporate some examples with transition metals along with roman numerals. So write the chemical formula of iron chloride and also iron nitrate. The chemical symbol of iron is Fe. The roman numerals tells you the charge on Fe. So the charge is positive 2 and chloride has a minus 1 charge.
And then use the same method, so this is going to be Fe1Cl2 or simply FeCl2. As you can see this is not difficult. The next one, Fe3Nit, this time Fe has a positive 3 charge, based on the Roman numeral.
Nitrate is a polyatomic ion with the formula NO3-1. So this is going to be Fe1NO3 times 3 due to the positive 3 charge. So we can simply write it as FeNO3-3.
So what do you think? Is this doable or is it too difficult? Here's some more examples that you can work on.
Copper 1 phosphate. And also, copper 2. Phosphide. So in the first example, copper has a plus one charge. Phosphate is PO4 with a negative three charge. So this is going to be Cu3PO4 times one.
If it's just a 1 as a subscript, we really don't need to write the 1, nor do we need to write the parentheses. So the answer is simply Cu3PO4. So that's copper 1-phosphate.
The next one, copper has a plus 2 charge, phosphide has a minus 3 charge. So this is going to be Cu3P2. And we can't modify the answer, so this is it.
Let's work on some harder examples. Tin 4 selenide. and lead for perbromate.
So go ahead and work on those examples. So in our first example, tin has a plus 4 charge. Selenide, which is associated with selenium, has a minus 2 charge. So initially, this is going to be Sn2Se4.
Now, if you can reduce the numbers, you should. Because they're both even, you could divide both numbers by 2. So therefore, the correct formula is going to be Sn1, which we don't have to write the 1, Se2. So this is the answer. The next one, lead, has a positive 4 charge, and perbromate is BrO4 with a negative 1 charge.
So this is going to be Pb1BrO4 times 4, or simply just PbBrO4 4. Go ahead and work on this one. Vanadium, 5. oxide. So in this example, vanadium has a positive 5 charge. Oxygen has a negative 2 charge. So using this method, it's going to be V2O5.
That's vanadium 5 oxide.