Dalton'S Atomic Theory
Dalton'S Atomic Theory
Dalton'S Atomic Theory
John Dalton was an English chemist, physicist, and meteorologist who was
born on September 6, 1766, in Eaglesfield, England. During his early career,
he identified the hereditary nature of red-green color blindness. In 1803 he
revealed the concept of Dalton’s Law of Partial Pressures. Also in the
1800s, he was the first scientist to explain the behavior of atoms in terms of
the measurement of weight. Dalton died July 26, 1844 in Manchester,
England.
The main points of Dalton’s atomic theory are:
1. All matter consists of indivisible particles called atoms.
2. Atoms of the same element are similar in shape and mass, but
differ from the atoms of other elements.
3. Atoms cannot be created or destroyed.
4. Atoms of different elements may combine with each other in a
fixed, simple, whole number ratio to form compound atoms.
5. Atoms of same element can combine in more than one ratio to
form two or more compounds.
6. The atom is the smallest unit of matter that can take part in a
chemical reaction.
Explanation
All matter consists of tiny particles called atoms. Dalton and others
imagined the atoms that composed all matter as tiny, solid spheres in
various stages of motion.
When elements react, their atoms may combine in more than one
whole-number ratio. Dalton used this assumption to explain why the
ratios of two elements in various compounds, such as oxygen and
nitrogen in nitrogen oxides, differed by multiples of each other.
Drawbacks of Dalton's Atomic Theory
The indivisibility of an atom was proved wrong: an atom can be
further subdivided into protons, neutrons and electrons.
Dalton said that atoms of same element are similar in all
respects. However, atoms of some elements vary in their masses
and densities. These atoms of different masses are called
isotopes.
Dalton said that atoms of different elements are different in all
respects. However in certain cases: argon and calcium atoms
each have an atomic mass of 40 amu. These atoms are known as
isobars.
The theory fails to explain the existence of allotropes; it does not
account for differences in properties of charcoal, graphite,
diamond.