History of the atom

Democritus

400

In 400 B.C, a Greek philospher named Democritus came up with the concept of the atom. He kept cutting paper into smalle pieces and figurd that at some point, it would be invisible. So he came up with the atom. When he thought of it, he only envision a small round ball. He didn't know of the nucleus or the proton or the electron, but did know that all matter is made of smaller particles.

Robert Boyle

Oct 15, 1663

Robert Boyle studied teh relationship between volume and pressure of gases. His experiment concluded that gas ismade of tiny particles that group together to form a new substance. He was one of the first to comment on the reactive nature of atoms.

John Dalton

Oct 21, 1803

John Dalton, and english chemist, came up with the Atomic Theory of Matter. Based on finding by Ancient Greek philosopher Democritus and his own reasearch, his theory states that:
- All matter is made of atoms.
- Atoms cannot be divided or destroyed.
- Atoms of a certain element do not differ in size, mass, or any other properties.
- Atoms of different elements combine to create chemical compunds.
- IN chemical reactions, atoms are combine, rearranged, or separated.

Dmitri Mendeleev

Oct 15, 1869

Discovered that the properties of elements were "periodic funtcions of their atomic weights". He hten separated simliar atoms into 7 groups, creating the periodic table, and the periodic law.

Henri Becquerel

Oct 15, 1869

While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.

Sir William Crookes

Jun 17, 1879

Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

Eugen Goldstein

Oct 15, 1886

Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.

J.J. Thompsons

Apr 15, 1897

Thompson predicted that there were smaller particles in every atom, so he use a cathode ray tube to prove that. With that discovery, he disproved Dalton's atomic mass theory and showed that particles can be divided. And through that experiment, he also inferred that atoms must be negatively charged.

Frederick Soddy

Oct 15, 1900

Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay.

Hantaro Nagoaka

Oct 15, 1904

Hantaro developed an early yet incorrect model of the atom. He called it, "The planetary model". HIs model was based arounf the planet Saturn. He explained thst the rings there were held for massive orbit. While his statement are incorrect, he is still credited for the discovery of atom rings.

Ernest Rutherford

Aug 4, 1909

Rutheford carried out his famous gold foil experiment, where he shot a positively charged beam of particles through a gold foil. He predicted that the particles would be soft enough to pass through the foil and continue in a straight line. While it somewhat i did, it helped disprove JJ Thompson's atomic model, encouraging Rutherford to create his own.

NIels Bohr

Oct 15, 1913

Niels Nohr, was the first scientist to suggest that electrons travel around the nucleus in infinite paths. He suggested the idea that electrons are placed a certain "level" waya from the nucleus. He also stated that electrons can change paths, but not jump from one path to the other.