Timeline Of The Discovery Of The Atom Flashcards
In 420 BC, who believed what about the atom?
Democritus believed matter to be composed of small particles with empty space between them
Who and when discovered the electron? What did it lead to?
In 1897, by Jj thompson
Lead to the plum pudding model
What did the plum pudding model suggest?
The atom was a ball of positive charge with negative electrons embedded in it
In 1909, which three people devised which experiment?
Geiger, Marsdon and Rutherford devised the scattering experiment
What did the scattering experiment involve?
Firing alpha particles at very thin gold foil
What was the prediction of the scattering experiment?
All of the positively charged alpha particles would be deflected a few degrees by the positive pudding of the atom
What actually happened in the scattering experiment?
Vast majority of the particles passed through, some particles bounced back 180 degrees
What did the evidence of the scattering experiment suggest?
- The mass of the atom lay mostly at the centre of the nucleus with the rest being mostly empty space
- as most particles had been repelled it suggested the nuclei of the gold atom must have been positively charged
What new model replaced the plum pudding theory?
The nuclear model
In 1913, who adpated the nuclear model and what did it suggest?
Neils Bohr, suggested the electrons orbit the nucleus in set distances or levels
Whose theoretical calculations agreed with the theory?
Bohr’s
What ideas did later experiments lead to?
The postive charge of any nucleus is made from smaller positive particles, each with the same sized charge
What were the smaller positively charged particles called?
Protons
In what year did James chadwick discover a third part?
In 1933, he discovered the existence of a third particle the neutron
Where was the neutron found?
In the nucleus with the protons but had no charge
What do atoms have a radius of?
1x10-10m
What is the radius of the nucleus?
LESS THAN 1x10-14m
What is the mass number always? What is the exception?
Mass number is always bigger than the atomic number
Expect for hydrogen were they are the same
What does all of the atoms identity depend on?
The number of protons
What are both neutrons and protons called?
Nucleons because they both exist in the nucleus
Why did most of the alpha particles from the scattering experiment pass through?
The atom was mostly empty space
What are the similarities and differences between the plum pudding model and modern nuclear model?
Similarities - both have a area of positive charge, both have electrons, both say the overall charge is neutral
Differences - PPM says positive charge isnt divided into smaller parts, PPM has no neutrons only electrons, PPM has mass spread evenly, but nuclear model has mass concentrated at the nucleus