Notes

*Democritus*: Created idea of tiny indestructible particles, coined term 'atom'. Did no experiments or actual science.
*John Dalton*: Reinvented atoms, with a theory with 5 points:
1. All matter is made of indivisible atoms.
2. Atoms cannot be created or destroyed.
3. All atoms of a particular element are identical.
4. Compounds are formed through the combination of elements.
5. Chemical reactions happen by atoms bonding or seperating from compounds.
1 and 2 were proven wrong by the later discovery of subatomic particles that can be seperated from the atom, and isotopes proved 3 wrong.
*J.J Thomson*: Using cathode ray tubes, Thomson noticed the ray moving toward a positively charged plate. Based on this, Thomson came up with the idea that cathode rays were made up of electrons, negatively charged particles which were normally part of atoms. His model of the atom was the plum pudding model, where the atom was a positive sphere with electrons embedded within.
*Ernest Rutherford*: Ernest Rutherford investigated radiation coming out of an atom. He found that radiation included positive (alpha particles/ He ions), negative (beta particles/electrons) and gamma (electromagnetic radiation) radiation. He shot radiation through gold foil, and found that more particles reflected than should have. This lead him to realise that rather than an atom being evenly distributed, it has a dense core (nucleus) and electrons around it floating in empty space.
*James Chadwick*: Chadwick realised an atom's mass did not make sense based on the theory only including protons and electrons, and figured out there must be a neutral subatomic particle.
*Niels Bohr*: Rutherford's model was too stable and did not explain line spectra. Bohr devised the model of specific orbits existing around the atom, which electrons must stay in - and that electrons could jump between shells with a burst of energy.
*Antoine Lavoisier*: Lavoisier published a list of the known elements and standardised their names.
*Wolfgang Döbereiner*: Noticed that several groups of three elements shared properties (i.e Li, Na and K).
*John Newlands*: Created law of octaves, the idea that when elements are ranked by mass, every 8th had similar elements. We now know that it is actually every 9th that has this characteristic, in what is now called the periodic law.
*Dmitri Mendeleev*: Father of the periodic table. Combined organisation of elements by characteristics and by mass, as he organised elements by rows by mass and by columns by characteristics, with every row being a period long. He was so confident in his theory that he left empty spaces on the table for undiscovered elements, along with predictions on their characteristics which were remarkably accurate.