Modeling Ionic Compounds
As you've learned, there are two main types of chemical bonding: ionic bonding and covalent bonding. You should know that an ionic bond is between a metal and a nonmetal, and should understand that it involves charged ions. It involves a nonmetal, which basically steals an electron (or two or three) from a metal. This makes the nonmetal negatively charged and the metal positively charged. Since opposites attract, they stick together in an ionic bond. But, these are words and scientists like pictures. So let's learn to draw pictures!
The Octet Rule
Remember when I told you the octet rule was super important? Well, it's about to become even more important. So, if you don't remember it, go back and review before continuing this lesson.
Lewis Dot Structures
There are several ways to show atoms forming molecules, including the one above (with Bohr models), but the most common is the Lewis dot structure. As it happens, they were invented by a guy named Lewis (how convenient that he managed to invent something with the same name as him!). They’re extremely simple to read: each dot represents a valence electron, and each atom is denoted with its atomic symbol. To draw them, start with the atomic symbol in the middle, and just keep putting dots in a clockwise circle until there are enough for one atom. To figure out how many are enough, just count the boxes on the Periodic table like we did with Bohr models. It looks a little something like this:
Modeling Ionic Compounds with Lewis Dot Structures
Modeling an ionic compound (and the chemical reaction that makes it) with Lewis dot structures is almost as easy as drawing a Lewis dot structure. It's just 3 easy steps:
- Draw Lewis Dot Structures for each atom in the molecule. If there is more than one instance of each atom, make sure to draw all of them!
- Transfer electrons from atom to atom (arrows). Make sure each gets 8 electrons. (Or 2, for H, Li, and Be.)
- Write out a chemical formula for your new compound. Remember, the charges of one ion should equal the coefficient on the other (criss cross rule).
Drawing Lewis dot structures and modeling ionic compounds isn't hard, but it is important to know these steps in order to understand our next step: modeling covalent compounds.