John Dalton’s Atomic Theory
Basic theory about nature of matter was given by the British chemist, John Dalton. His theory was on the fundamentals of laws of chemical combination. His theory explained law of conservation of mass and the law of definite proportions extensively.
He gave his atomic theory in 1808 according to which all matter (element, compound or mixture) is made up of small particles called atoms. The postulates of Dalton’s atomic theory are:
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- Matter consists of very tiny particles called atoms.
- Atoms are of indivisible nature which cannot be created or destroyed in a chemical reaction.
- Mass and chemical properties of atoms of a given element are identical.
- Different element atoms have different masses and chemical properties.
- Compounds are formed by combining atoms in the ratio of small whole numbers.
- In a given compound, the relative number and kinds of atoms are constant.
Law of conservation of mass is related to Dalton’s fourth postulate. Every atom of an element has a definite mass. Rearrangement of atoms takes place in a chemical reaction. Thus after the reaction, mass of the product should remain the same. Law of definite proportions is explained in the fifth postulate.
A compound consists of matter having atoms of two or more elements in small whole number ratio. As the atoms have definite mass, the compound must have the elements in definite proportions by mass.
The Dalton’s atomic theory also predicted the new theories like law of multiple proportions on the basis of his theory. The deduction of law of multiple proportions from atomic theory was important in convincing chemists of the validity of the theory.
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So, Dalton’s atomic theory explains states that:
- All matter is made of atoms. Atoms are indivisible and indestructible.
- All atoms of a given element are identical in mass and properties
- Compounds are formed by a combination of two or more different kinds of atoms.
- A chemical reaction is an arrangement of atoms.
Modern atomic theory is, of course, a little more involved than Dalton’s theory but the essence of Dalton’s theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions.
Many heretofore unexplained chemical phenomena were quickly explained by Dalton with his theory. Dalton’s theory quickly became the theoretical foundation in chemistry.
Symbols for every element were firstly used by Dalton in a particular way. His symbolization for an element defined a definite quantity of that element, i.e one atom of that element. Berzilius idea for the symbols of elements was to use one or two letters of the name of the element.
Initially the names of elements were derived from the name of the place where they were found for the first time.
Example: Copper was taken from Cyprus.
Some names were taken from specific colours.
Example: Gold was taken from the English word meaning yellow.
