John Dalton
John Dalton (September 6, 1766 - 27 July 1844) was a British school teacher with a Quaker background. He was also chemist, meteorologist and physicist. He is known for his atomic theory also called the Billiard Ball Model and for his research into colour blindness, sometimes referred as "Daltonism" in his honour.
How did he discover the atom?Dalton knew there are different types of atoms called "elements", for example, hydrogen, oxygen and nitrogen. The elements differ from each other by their weights, however atoms of the same element all have the same mass while atoms of different elements are different in mass. He imagined atoms to be tiny spheres so he drew them as circles. He used patterns within the circles to distinguish the different elements. In this manner, he symbolized atoms to experiment with their combining properties. With the information, he created a "Table of Atomic Weights" and placed them in order of their masses, comparing them to hydrogen, the lightest element, which is number one on the table and has the atomic number of 1.
Dalton formulated his Theory of Multiple Proportions and Theory of Definite Composition. Because he claimed that atoms were solid spheres, his model is also referred to as the "Billiard Ball" Model. |
Postulates of Dalton's Theory
- All matter consists of indivisible particles called atoms.
- Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements.
- Atoms cannot be created or destroyed.
- Atoms of different elements may combine with each other in a fixed, simple, whole number ratio to form compound atoms.
- Atoms of same element can combine in more than one ratio to form two or more compounds.
- Atoms are the smallest unit of matter that can take part in a chemical reaction.