http://www.ck12.org Chapter 3. Chemical Interactions
Like water, all compounds consist of a fixed ratio of elements. It doesn’t matter how much or how little of a
compound there is. It always has the same composition.
FIGURE 3.3
All water molecules have two hydro-
gen atoms (gray) and one oxygen atom
(blue).Q:Sometimes the same elements combine in different ratios. How can this happen if a compound always consists
of the same elements in the same ratio?
A:If the same elements combine in different ratios, they form different compounds.
Same Elements, Different Compounds
Look at theFigure3.4 of water (H 2 O) and hydrogen peroxide (H 2 O 2 ), and read about these two compounds. Both
compounds consist of hydrogen and oxygen, but they have different ratios of the two elements. As a result, water
and hydrogen peroxide are different compounds with different properties. If you’ve ever used hydrogen peroxide to
disinfect a cut, then you know that it is very different from water!
FIGURE 3.4
Water: Water is odorless and colorless.
We drink it, bathe in it, and use it to wash
our clothes. In fact, we can’t live without it.
Hydrogen Peroxide: Hydrogen peroxide is
also odorless and colorless. It’s used as
an antiseptic to kill germs on cuts. It’s also
used as bleach to remove color form hair.