Compounds and Mixtures
Compound – a substance whose smallest unit is made up from atoms of more than one
element together.
 They often have properties that are different from the elements that make it up.

Example: Water is made up of hydrogen and oxygen.
If you break water down into hydrogen and oxygen, it is no longer water.
Compounds have formulas. The formula tells you what elements make up the compound and
how many atoms of each element.
Example:
o H2O is the formula for water. It has two hydrogen atoms and one oxygen atom.
o H2O2 is the formula for hydrogen peroxide. It has two hydrogen atoms and two
oxygen atoms.

Adding and extra atom of oxygen changes the substance completely.

The formula is always the same for a compound, no matter how much of it you have.
o Example: for the compound water, if you have 12 atoms of hydrogen and 6 of
oxygen, you have 6 molecules of H20 (6H20) not H12O6
Quick Tip: Reading a formula
The number in the front tells
how many molecules of the
compound there are
10H2O2
The little numbers (subscripts) tell you how
many atoms of that element there are. If there
is no subscript, there is one atom.
Mixture – when two or more substances come together but don’t combine to make a new
substance.
Example:
o Your bowl of cereal in the morning (the cereal and milk don’t combine)
o Chocolate milk – the chocolate syrup just dissolves – it doesn’t make a new
substance.

The amounts of the substances in a mixture can be changed without changing what the
mixture is.
Example:
o You can add more sand to a mixture of sand and water, but it will still be just a
mixture of sand and water.
Heterogeneous mixtures – a mixture that has larger parts that you can see
Example:
o vegetable soup – you can see the vegetables in it.
Homogeneous mixtures – the mixture is the same throughout – you can’t see the different parts
in this type of mixture - if the substances are dissolved, the mixture is homogeneous
Example
o iced tea – you can’t see the sugar separate from the water.

Another name for a homogeneous mixture is a solution.

A solute is the substance that gets dissolved.

A solvent is the substance the solute is dissolved into.
o Example: Koolaid and water. Koolaid is the solute, while water is the solvent.