John Dalton’s atomic theories were introduced in 18 hundreds England. In September of 1803,
John Dalton wrote his first table of atomic weights in his daily journal. Two years after he
developed his atomic weights, he put them in a book called "A New System of Chemical
Philosophy.” In it he was the first to discover that elements should be identified with symbols.
However, only 3 or 4 pages in the third chapter of his book said the atomic theory he
discovered. In this theory, there are five basic thoughts.
1. Chemical elements are made of atoms.
2. The atoms of an element are identical in their masses
3. Atoms of different elements have different masses
4. Atoms only combine in small, whole number ratios such as 1:1, 1:2, 2:3 and so on.
5. Atoms can be neither created nor destroyed
however, he made a mistake in thinking atoms of element in a 1:1 ratio, and his system
of atomic weights was not correct. He gave oxygen an atomic weight of seven instead
of eight.
The idea of atoms had been discovered much earlier. The Greeks had talked about atoms, but
Dalton's theory was different because he had the weight of chemical measurements behind it.
His atomic theory stated that elements consisted of tiny particles called atoms. He said that the
reason an element is pure is because all atoms of an element were totally the same and
particularly they had the same mass. He also said that the reason elements differed from one
another was because atoms of each element were different from one another. Basically saying
they had different masses. He also said that compounds consisted of atoms of different
elements combined together. Compounds are pure substances because the atoms of different
elements are together somehow, and are not easily separated from one another. Compounds
have constant composition because they contain a specific ratio of atoms and each atom has its
own weight. In conclusion he said that chemical reactions involved the rearrangement of
combinations of atoms.