chemistry - excel textbook - theories

1.1 Daltons Theory - “billiar atom”

- Matter is made up of small dense particles called atoms. - Atoms are each element are identical. - Atoms are indestructible.

Problems which arose:

Because Dalton did not believe that elements could be diatomic, his theory could not explain Gay Lussacs Law of combining volumes. A Avogadro had solved the problem of correctly determining atomic weights as early as 1811. He also realised that ultimate particles of gases could be diatomic and was the first chemist to write the formula of water correctly. It was not until Avogadro’s Law was accepted that polyatomic elements were said to exist and the difference between atoms and molecules was understood.

1.2 The electrical atom

Thomson showed that identical cathode rays were produced by different elements. He suggested that these cathode rays were small negatively charged particles which he called electrons. Atoms are positively charged spheres containing negativ...