History Of The Atom Flashcards
Learn the development of the history of the atom and who carried out the experiments
What did Democritus believe?
(400BC)
All matter is made of invisibe, indestructible and homogenous atoms, (“atomos”).
There are different types of atoms that differ in shapes, sizes, masses and properties specific to the matter.
For example, wood “atomos” would make up wood and a different atom would make up fur.
What did Aristotle believe?
(340BC)
Everything is made uo of five elements
Everything is a combination of these elemnts
The elemnts were: Fire, Water, Earth, Air and Aether (divine element)
What did John Dalton’s theory say?
(1803)
All matteris composed of small particles called atoms.
Atoms are indivisible and indestructible.
Atoms of a given element are identical in sizes, mass and chemical properties.
Atoms of a specific element differ of those of another element.
Different atoms combine in simple whole number ratios to form compounds in a chemical reaction atoms are seperated, combined or rearrnged.
Who came after John Dalton?
J.J.Thomson
(1897)
What did J.J.Thomson discover, and how?
The electron, in 1897
Through a series of experimens desgned to study the nature of electrical discharge in a high vacuum cathode-ray tube.
What did J.J.Thomson’s discovery mean?
Since the electron was so small he thought it came from within the atom.
This meant the toms was no longer the smallest thing that existed and could be divided, the Greek and John Dalton’s theories were no longer true.
What was J.J.Thomson’s atomic model?
(1904)
The Plum Pudding Model:
it was a positive body/structure with negative electrons within.
(The positive strucutre was the pudding and the electrons were the raisins dotted about.)
Who came after J.J.Thomson?
Ernest Rutherford (1911)
What experiment did Ernest Rutherford carry out?
Alpha particle scattering experiment:
shot alpha particles at gold foil.
What results came from Ernest Rutherford’s experiment?
a few alpha particles deflected
Very few (1 in 8,000) bounced back
Most went straight through the gold foil unaffected
What conclusions could be made from Ernest Rutherford’s results?
Most of the atom is empty space -
as most of the particles went stright through unaffected the atom could not be a positive structure otherwise it would have bounced off or deflected more often.
Most of the mass is contained in the centre, nucleus, and thats the centre is dense small and heavy -
since the alpha particles bounced off whatever caused this ust be very heavy, but as so few particles did bounce off this mass nust also be small as it very seldom collided.
What was Ernest Rutherford’s atomic model?
It was a planetary model:
It had a positively charged centre, surrounded by negatively charged, orbiting electrons.
Most of the mass is in the centre of the atom and the rest is mostly empty space.
What questions were left unanswered by Erenest Rutherford’s findings?
How did the densely packed, postiviely charged protons not repel each other in the nucleus ( as like charges repel)?
The total mass did not add up, as there another sub-atomic particle?
Who came after Ernest Rutherford?
James Chadwick
(1932)
What did James Chadwick discover?
A new sub-atomic particle without charge, within the nucleus.
it was called the neutron.
