Okay, so it turns out that there's two types of ways that in which two or more atoms can come together to form compounds. The two types of bonds are one covalent bonds and the second one is the ionic bond. The name of these two types of bonds tries to tell you what's going on between the atoms. Covalence are sharing covalence electrons. So a covalent bond is between two atoms who are sharing valence electrons. These can come in a couple of varieties. One, there is the single bond, single covalent bond, where the atoms are sharing two valence electrons. The double bond is, you can think of it as two single bonds, where they are sharing two pairs of electrons for a total of four. So four total and the last one would be triple bond, a triple covalent bond, where the atoms are sharing three pairs of electrons for a total of six. Now, on contrast, the ionic bond is the attraction between two ions. Okay, so ions are atoms or molecules that have a net positive or negative charge. So in an ionic bond, we have a positively charged ion that is electrostatically attracted to a negatively charged ion. And that electrostatic attraction between the positively charged ion and the negatively charged ion is the ionic bond. This can result from the transfer of electrons, which we'll talk about in a little bit, where one atom loses an electron or transfer is an electron to another atom. And that result is a positive charge ion for the atom or molecule that just lost an electron and a negative charge for the atom that just gained an electron. So what are the two different scenarios in which an ionic bond or a covalent bond would set up? Well, it turns out that most of the time, not all the time, but most of the time covalent bonds form between non-metal atoms. And ionic bonds form between a metal and a non-metal. Okay, this has to do with primarily differences in electron negativity, which we'll talk about in a little bit. And then of course, how either of these atoms are going to satisfy what is known as the octet rule. Before we get to the octet rule, let's just talk about how we display compounds in what are known as molecular formulas. Now you've already seen these most likely at some point in time, either in the different science course or reading through the textbook. What we do is we show molecular formulas in this fashion. Say we have water. Water is of course H2O. And it's H2O because there are two hydrogen atoms and one oxygen atom. Now whenever there's just one oxygen, one atom of any type, we don't need to show the subscript. So if you don't see a subscript there, you know there's just one of them. But any time you have more than one atom, you're going to show that in a formula by showing a subscript to the right of that element. The atoms elemental symbol. And that shows you how many different atoms are there. If we wanted to show the molecular formula for the sugar molecule glucose, it turns out each glucose atom has six carbons. So we would write C in a subscript 6 as 12 hydrogen atoms. And then 6 additional oxygen atoms. So the molecular formula for glucose is C6H12O6. And so that's how we would write it in terms of a formula. Now eventually when we start talking about polyatomic ions, you'll notice that we will need to use parentheses. So a very common one type of base would be calcium hydroxide. That calcium hydroxide is the calcium ion and two hydroxide ions which are polyatomic ions. Now if we were to just write CAOH2, you might look at this formula and think that there's one calcium atom, one oxygen atom and then two hydrogen. But it turns out there's two hydroxide which is OH. And so we need to show a parentheses around that hydroxide. So now that we know that there are two hydroxides and one calcium. So in terms of this, we just basically factor in this subscript on the outside of the parentheses. So each calcium hydroxide compound has two or excuse me, one calcium, two hydrogen and two oxygen atoms.