Atomic Models throughout history Models to represent the of the atom have changed over time. was an ancient Greek philosopher who was born in 460BC. He described matter as being made up of indivisibles ( ). This is where the name came from. In , atomis means uncuttable. The ancient Greeks adopted the belief that all matter is made up of Earth, Water, Fire and Air. Ideas about atoms and their structure didn’t change much for almost In 1808, an English chemist, John made up of years. described matter. He believed matter is , indivisible (unable to be divided ….NOT invisible) particles which he calls atoms. Joseph J Thomson, an English , described atoms like a plum pudding. The description was known as the plum model. In this model atoms were presented as having a heavy positive pudding with the light negatively charged embedded in it. The discovery of radioactivity allowed scientists to examine atoms in Rutherford used radioactive ways. Ernest to find out that atoms had a tiny, very dense, positively charged nucleus with electrons atoms contained mainly the nucleus. He concluded that space. The Danish physicist, Niels Bohr improved on Rutherford’s model in . Bohr’s model has electrons in orbits with definite and amounts of energy. James Chadwick discovered and identified the . The neutron is a neutral particle found in the nucleus. In 1932, a new atomic model was developed. It was developed using ideas about atoms and the work of several new scientists. The model indicated that most of an atom’s mass is in the . and neutrons are found in the nucleus. The electrons can be found in very definite areas around the nucleus but are constantly . The Standard Model is the commonly used atomic model in modern science. It is based on the previous model but has more arrangements of electrons around the atoms. Word List…… Previous, 2000, new, solid, neutron, complex, electrons, Democritus, pudding, atom, Protons, Greek, orbiting, empty, Dalton, structure, atomis, 1913, physicist, particles, nucleus, positions, moving.