http://www.ck12.org Chapter 4. Atomic Structure
Compound A4 .08 g Cu
2 .28 g Cl=
1 .79 g Cu
1 .00 g Cl
Compound B
7 .53 g Cu
8 .40 g Cl=
0 .896 g Cu
1 .00 g ClCompare the masses of copper per gram of chlorine in the two samples.
1 .79 g Cu (in compound A)
0 .896 g Cu (in compound B)=
2. 00
1
=2 : 1
The mass ratio of copper per gram of chlorine in the two compounds is 2:1.
Step 3: Think about your result.
The ratio is a small whole-number ratio. For a given mass of chlorine, compound A contains twice the mass of
copper as compound B.
Dalton’s Atomic Theory
In 1808, an English chemist and schoolteacher named John Dalton (1766-1844) formulated an atomic theory based
on the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. His theory
can be summarized in the following statements, illustrated below (Figure4.4).
- All matter is composed of extremely small particles called atoms.
- Atoms of the same element are identical in terms of size, mass, and other properties. Atoms of one element
are different from the atoms of any other element. - Atoms of different elements can chemically combine with one another in simple whole-number ratios to form
chemical compounds. - Chemical reactions can be described as the separation, combination, or rearrangement of atoms. Atoms of one
element cannot be changed into atoms of a different element as a result of a chemical reaction.
FIGURE 4.4
Dalton’s atomic theory states that chem-
ical reactions are due to rearrangements
of atoms. On the left, hydrogen molecules
are shown as two H atoms, while oxygen
molecules are shown as two O atoms.
The chemical reaction forms water as
the atoms rearrange. There are identical
numbers of hydrogen and oxygen atoms
before and after the reaction.