You must first learn why atoms bond together. We use a concept called "
Happy Atoms." We figure most atoms want to be happy, just like you. The idea behind Happy Atoms is that atomic shells like to be full. That's it. If you are an atom and you have a shell, you want your shell to be full. Some atoms have too many electrons (one or two extra). These atoms like to give up their electrons. Some atoms are really close to having a full shell. Those atoms go around looking for other atoms who want to give up an electron.
Let's take a look at some examples.
We should start with the atoms with atomic numbers between 1 and 18. There is a 2-8-8 rule for these elements. The first shell is filled with 2 electrons, the second is filled with 8 electrons, and the third is filled with 8. You can see that sodium (Na) and magnesium (Mg) have a couple of extra electrons. They, like all atoms, want to be happy. They have two possibilities. (1) They can try to get eight electrons to fill up their third shell. Or (2) they give up a few electrons and have a filled second shell. For them it's easier to give up a few electrons.
What a coincidence! Many other atoms are interested in gaining a few extra electrons.
Oxygen (O) and fluorine (F) are two good examples. Each of those elements is looking for a couple of electrons to make a filled shell. They have one filled shell with two electrons but their second shell wants to have eight. There are a couple of ways they can get the electrons. (1) They can share electrons, making a covalent bond. Or (2) they can just borrow them, and make an ionic bond (also called electrovalent bond).
So we've got a sodium (Na) atom that has an extra electron. We've also got a fluorine (F) atom that is looking for one.
They wind up working together and both wind up happy! Sodium (Na) gives up its extra electron. The sodium (Na) has a full second shell and the fluorine (F) has a full second shell. Two happy atoms! That's one way things are able to bond together. They can give up or share electrons. The two elements have created an ionic bond.
Source: www.chem4kids.com
