Atomic Theory (by Daniel Rain) timeline

Democritus was born in 460 BCE, not 1750 Intro: Democritus was born in Abdera, Greece in 460 BCE and died in 370 BCE. Discovery: Democritus hypothesized that all matter consisted of tiny, indivisible particles. This was proven later on. Experiment: Democritus took a seashell, repetitively broke it in half until he was left with an “indivisible piece.” Of course what he was left with wasn't a particle but he was heading to something that is the building block for all atomic theory.

Intro: John Dalton was born in England and lived from 1766-1844. Discovery: Dalton discovered that all matter was made of indivisible and unbreakable building blocks called atoms. All atoms in an element are identical but different elements had atoms that varied in size or mass. Experiment: He measured how much water vapour could be absorbed by different gases like hydrogen and oxygen.

Intro: J.J Thomson was born in Cheetham Hill, England and lived from 1856-1940. Discovery: Joseph John Thomson discovered electrons. He also recognized that the atom is positive yet has negative electrons in it. Experiment: Thomson looked at electric currents in glass tubes called cathode ray tubes and caused non-radioactive atoms to produces streams of negatively-charged particles called electrons.

Intro: Ernest Rutherford (1891-1937) was a New Zealander scientist. Discovery: He discovered that all atoms have a positively charged nucleus which is very dense and therefore have electrons orbiting around it. Experiment: Rutherford took a sheet of golden foil andstruck a beam of alpha particles at it, he noticed a small amount of the particles were deflected. He concluded that is was a tiny, dense nucleus that caused these deflections.

Intro: Niels Bohr is was a Danish scientist born in Copenhagen. He lived from 1885-1962. Discovery: Bohr discovered that electrons moved in separate orbits revolving around the nucleus. The number of electrons determines the properties of an element. Experiment: He knew all compounds had different properties so he worked backward and realized this phenomenon.

Intro: James Chadwick was a physicist in England. He lived from (1891-1974.) Discovery: James Chadwick discovered the particle found in a nucleus known as the neutron. Experiment: James projected alpha particles towards Beryllium. Then the particles that pass the Beryllium and fall on a paraffin wax are neutrons.