So density represents the amount of mass per units of volume. And here we have our purple box again. Remember when we have a purple box, that means that is a formula or some type of concept you need to commit to memory. So density is equal to mass over volume.
Depending on the phase of matter, the units forward can be different. So we're going to say for solids and liquids, which are more dense than gases. Solids and liquids have the unit for mass in grams and a unit for volume in milliliters, or they have the unit for mass still in grams or the units for volume in centimeters cubed. Remember when we talked about conversion factors for volume? We said that one milliliter was equal to 1cm3. That's why we're allowed to basically swap out MLS here for centimeters, cubes here.
Now, gases themselves are much less dense than solids and liquids, so their units for density are a little bit different. Their mass is still in grams, but now because they're less dense, we wouldn't use milliliters, we'd use liters. And remember, within our conversion factors, we said that one liter was equal to 1dm3. So we could say the density of gases is grams per liter or grams per decimeters cubed.
So just remember, density itself is just massive over volume. Depending on the phase of matter that we're dealing with, the units can be slightly different. Now that we've looked at the basic setup of density, let's move on to our example and practice questions.