1. 1.3.1 Solids, Liquids and gases

2. Density
System property = mass
Material property = density ( = m/V)

3. Density is the measure of the “compactness” of a material
The proximity of like atoms or molecules
More than just the “heaviness” of a substance, density includes how much space an object takes up!!
All substances have density including liquids, solids, and gases, although the densities of gases are calculated rather than measured.
Densities of gases are stated at specific points as they change.
STP is 273K and 100kPa

4. FACTORS AFFECTING DENSITY

5. Atomic Spacing Clearly atomic spacing has lots to do with density.
More molecules or atoms in the same space will result in a more dense material.

6. BUT it is also the same as
ρ = m/V
BUT it is also the same as
the mass of one molecule x
the number of molecules in a cubic metre
(think about it!)

7. Molecular spacing ASSUME that every molecule is spherical.
If we put molecules into a 1m3 box with spacing between them of x.
The number of molecules along the edge is 1/x

8. For the volume of the box we cube the length of the side SO ....
For the total number of molecules in the box we cube the number along one edge.
= (1/x)3