A Brief History of Atomic Theory
All matter is made of small indivisible and indestructible particles called atoms
There are an infinite amount of atoms and the world is composed only of atoms, and the space within the atoms exist (void)
Everything is composed of atoms except earth, air, fire, and water
Change does not occur through the rearrangement of atoms, but through the transfer of matter
Dalton concluded that evaporated water exists in air as an independent gas. He wondered how water and air could occupy the same space at the same time, when obviously solid bodies can't. He then realized that water and air must be composed of separate particles. Through experimentation he realized that H2O was composed of the elements hydrogen and oxygen.
Other purified substances also could be separated into elements.
Concluded that atoms are indivisible and indestructible, all atoms of the same element are identical in mass and properties, chemical reactions are the rearrangement of atoms and compounds are formed by the combination of two or more different atoms.
Experiment: vacuum tube with two wires. run charge through the tube=neon glow.
Deflections of rays=something smaller than the atom=negatively charged electrons.
The atom is a sphere of positive matter, with electrons positioned based electrostatic forces.
Plum pudding atomic model.
Initially studying radioactivity, studying the effect of x-rays on various metals
Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles. He decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil but to his amazement a few alpha particles rebounded almost directly backwards.
1 out of 20,000 particles did not pass through the screen and were fired back out
Concluded that the atom was mainly empty space with a dense positively charged mass at the center.
The dense positively charged mass was relatively small compared to the rest of the atom.
Electrons surround the outside of the positively charged mass.
Did not conduct experiments but used the work of other scientists, specifically Rutherford
Electrons orbit in fixed orbitals
Energy or each orbit directly relates to each side
These theories only worked for the hydrogen atom
Electron Cloud Model: Erwin Schrodinger
Predicted the probability of where electrons would be.
