-
500
Democritus
460-370 B.C.
He said " Atoms cannot be created, destroyed, or further divided."
He also said atoms move through empty space. -
Aug 24, 600
Aristotle
384-322 B.C.
He disagreed with the idea that atoms move through empty space.
He completely denied the existence of atoms.
His ideas overtook Democritus' idea about matter. -
Period: to
John Dalton
He revised Democritus' ideas based on his own research.
He said "atoms are the smallest particles of matter and are indivisible and indestructible."
To explain the conservation of mass he said "atoms can be rearranged, separated, or combined to form new things, but cannot be created, destroyed, or divided in the process." -
Period: to
Sir William Crookes
He saw a green flash of light in a cathode ray tube and discovered what are now called electrons. -
Period: to
J.J. Thompson
He designed a series of CRT experiments to determine particle charge to mass ratio.
He disproves Dalton's theory about atoms are invisible.
Received Nobel peace prize in 1906 for his research discovery of electron. (The first subatomic particle) -
Period: to
Robert Millikan
He designed an oil drop apparatus to tell the charge of atom. -
Period: to
Ernest Rutherford
He discovered that the atom was mostly an empty space for electrons to move in. His model shows the neutral nature of matter with the balance of positive charges in nucleus and negative charges of electrons around the nucleus. -
Period: to
James Chadwick
He found neutrons
