2.1 Dalton’s Atomic Theory
Figure 2.1: John Dalton (1803-1807)
- All matter is composed of tiny particles called atoms. An atom is the smallest unit of an element that can participate in a chemical change.
- All atoms of a given element have identical chemical properties that are characteristic of that element.
- A compound consists of atoms of 2 or more elements combined in a small, whole-number ratio.
- Atoms can change how they are combined, but they are neither created nor destroyed in chemical reactions.
The Law of Conservation of Mass states that there is no detectable change in mass during an ordinary chemical reaction The Law of Constant Composition/Law of Definite Proportion states that one chemical sample will be the same as another chemical sample A chemical compound always contains the same elements in the same proportions by mass Aspirin will always have 9 Carbon, 8 Hydrogen and 4 Oxygen Atoms
Figure 2.2: John Dalton (1803-1807)
The Law of Multiple Proportions (Dalton’s Law) states that When two elements react, the mass of one element will react with masses of a second element so compounds always equals a ratio of small, whole number.
Compound A
32 grams of O reacts with 24 grams of C
\[\mathrm{ratio} = \dfrac{\mathrm{O}}{\mathrm{C}} = \dfrac{32}{24} = 1.33\]
Compound B
64 grams O reacts with 24 grams of C
\[\mathrm{ratio} = \dfrac{\mathrm{O}}{\mathrm{C}} = \dfrac{64}{24} = 2.66\]
\[\dfrac{\mathrm{Compound~A}}{\mathrm{Compound~B}} = \dfrac{2.66}{1.33} = \dfrac{2}{1}\]
Compound B has 2 O for every C; compound A has 1 O for every C.