Comparing Densities
307-9 Explain the effects of changes in temperature on
the density of solids, liquids and gases and relate the
result to the particle model of matter.
307-10 Describe situations in life where the density of
substances naturally changes or is intentionally
changed
We have learned that solids usually have
greater densities than liquids and liquids
usually have greater densities than gases.
 Why? Because solids have particles that
are more tightly packed together than
liquids and liquids are more tightly packed
than gases.
 Exception to the rule: mercury is a metal
that is liquid at room temperature, but
more dense than many other solids.

Each substance has its own characteristic density.
Scientist are able to use the density of a substance to
identify an unknown substance.
Substances besides water appear in different states
on Earth.
Rock, which is a solid on the Earth’s surface, is a
liquid beneath its crust
We see the liquid rock when a volcano
spews molten rock or lava to the surface
Heat decreases the density of the rock and allows it to
flow.
How does density help engineers?
Knowing the density of substances allows engineers to
design dams, build ships and reinforce concrete to
avoid stresses that may break structures like bridges
apart.
How does density help
manufacturers?
Density allows manufacturers to make moulds, create
alloys, and design material such as plastics to fit a number
of application from toys to automobiles.
What are some things on Earth that
can change naturally?
1. Ice – changes from a solid to a liquid
2. Rock – Changes from a liquid to a solid.
3. Chocolate – changes to a liquid if heated or left
in the sun.
As heat is added to a substance
what happens to the molecules?
The motion of the molecules will increase when
heat is added and increased. The higher the heat the
faster the molecules move.
Explain the density in this picture
Understanding Concepts
Make a general statement comparing
the densities of solids, liquids and
gases
Solids are more dense.
Liquids are less dense than solids
Gases are least dense
What substances have the greatest
density and why?
Solids have the greatest densities because the
particles in the solids are packed tightly together
and there is little space to move.
What substances have the least
densities?
Gases have the least densities because the particles
in gases are not packed tightly together and move
around more freely.