By: Ashley Morgan

Periods: 3rd & 4th

Atomic Theory Timeline

Atoms are the fundamental building blocks of matter.

The Atomic Theory

442 B.C. DemocritusDemocritus stated

that all matter is made up of

atoms.  He also stated that they are so small that they can’t be divided,

and they entirely fill up the space they’re

in. 

384-322 B.C. Aristotle

Aristotle provided the method of

gathering scientific facts, which proved as the basis for all

scientific work.

1777 Antoine LavoisierLavoisier is the founder of modern

chemistry. He showed that chemical

elements were neither created nor destroyed,

just combined into different compounds in chemical reactions. In

other words, he distinguished between

an element and a compound.

1799 Joseph Louis Proust

Proust is known for the Law of Definite proportions. This

states that a chemical compound

always contains exactly the same

proportion of elements by mass.

1803 John Dalton

John Dalton formed the atomic

theory, which states that all

matter is composed of tiny,

indestructible particles called

atoms. They are all alike and have the

same atomic weight. 

1832 Michael Faraday

Faraday developed the

Laws of Electrolysis. This is the splitting of

molecules with electricity.

1896 Henri Becquerel

Becquerel is noted for the discovery of

Radioactivity.

1898 Marie & Pierre CurieThe Curies stated

that radioactive materials cause atoms to break

down spontaneously,

releasing radiation in the form of energy and

subatomic particles.

1898 J.J ThomsonThomson discovered the electron

and developed the plum-pudding model of the atom.

1900 Max Planck

Planck stated that energy is radiated

in small units, which he called quanta.

1905 Albert Einstein

Einstein stated light was made up of

different particles, that, in addition to wavelike behavior,

demonstrate certain properties unique to

particles.  

1908 Robert Milikan

Millikan was able to find out the

electric charge of the electron. 

1909 Ernest RutherfordRutherford used the

results of his gold-foil experiment to state that all the mass of an atom were in a small

positively-charged ball at the center of

the atom. 

1913 Neils Bohr

Bohr stated that the electrons moved

around the nucleus in successively

large orbits.

1931 James ChadwickChadwick is noted for the discovery of the neutrally-

charged neutron.