The Atomic Theory of Matter

1. The Atomic Theory of Matter By Shaffer Lisle

2. The First Theories • John Dalton’s proposed theories: • Each element is composed of particles called atoms. • All atoms in an element have identical mass and other properties. Atoms of one element are different from that of another element. • Atoms are not changed into atoms of a different element by chemical reactions; they are neither changed nor destroyed during chemical reactions.

3. John Dalton’s Theory and Its Change • John Dalton’s theory says that atoms are the smallest particles that still retain chemical identity of an element. • With new technology we have found subatomic particles within atoms. • A lot of things are still considered correct with John Dalton’s theory even today.

4. The Discovery of the Electron • The electron was found when scientists started to study cathode ray tubes. • Cathode ray tube: pumped almost empty of air (vacuum tube). • A high voltage produces radiation within the tube. The radiation is known as cathode rays because it comes from the negative electrode or cathode.

5. The Discovery of the Electron • There were conflicting views about cathode rays. It wasn’t clear whether they were a stream of particles or a form of radiation. Experiments showed that they were deflected by electric or magnetic fields in a consistent way of their being a stream of negative charge. The British Scientists J.J. Thomson observed that the rays stayed the same regardless of the cathode material. His discoveries were considered the discovery of the electron.

6. Subatomic Particles • The rest of the subatomic particles were found when scientists made theories on where the electrons were in an atom. In 1910, a scientist named Rutherford examined the effects of passing alpha rays through a gold foil a few thousand atoms thick. He found that most passed right through the gold foil while some were deflected. This was later concluded that there is a lot of empty space in an atom and that they mostly passed through the empty space ,sometimes getting deflected by the later discovered nucleus (made up of protons and neutrons).

7. The Modern Atomic Structure • The modern atomic structure is mainly the protons and neutrons in the nucleus, with electrons moving in the open space in the atom.

8. The End By Shaffer Lisle