A Look at Density and How to Calculate It

Definition of DENSITY: The RATIO of the mass of a substance to the space it takes up (volume) Substances have a characteristic density Determined by how compact the atoms are inside

The maximum density of MOST materials occurs in the SOLID phase… solids have high densities gases have low densities

Can you think of an exception to this rule?

What happens to the molecules in liquid water as water freezes?

Molecules move farther apart and EXPAND! Ice (solid water) is LESS dense than liquid water It floats in liquid water!

Will it Float? Density can predict if something will float. How?

Will it Float? The density of liquid water is 1 g/mL. Objects with a HIGHER density than water will ________. Think of some examples…

It Floats If it has LOWER density, it will ________. Think of some examples…

Other factors that affect DENSITY: The density of a GAS varies with pressure and temperature: Higher temperature – molecules farther apart – LESS dense Lower temperature – molecules closer together – higher pressure - MORE dense

Units for Density Just like length, volume and mass, density has to be labeled with the correct unit… g/cm³ or g/mL is the standard unit for density. 1cm³ = 1mL