Development of the atom Flashcards
What where atoms thought to be before the discovery of the electron?
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
What did the discovery of the electron lead to?
The discovery of the electron led to the plum pudding model of the atom
Who discovered the plum pudding model?
J.J Thompson (1897)
What did the plum pudding model say about the atom?
The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.
Who proved the plum pudding model as wrong? How?
Ernest Rutherford (1905). With the results of the alpha scattering experiment.
What happened in the alpha particle scattering experiment?
Beams of positively charged alpha particles were directed at a very thin gold sheet suspended in a vacuum.
Why was the vacuum important?
The vacuum meant that the gold foil would be the only reason for any deflection of the alpha particles.
Why was gold foil used?
The gold foil was used because gold was the only metal that could be rolled very thin without cracking.
What would have happened if the plum pudding model was correct?
The alpha particles would pass straight through the thin foil, and any outliers may possibly puncture it or be only slightly deflected.
What were the actually results of the experiment?
Most went straight through but a larger number than expected came straight back and were deflected.
What did this show?
Plum pudding model couldn’t possibly be right.
Why?
.Passing straight through - atom mostly empty space
.Deflection at larger angles - suggested a concentration of positive charged mass that repelled them (nucleus)
.small number of alpha particles came straight back - conc of positive charge was also small
. the electrons were in a cloud surrounding the nucleus - atom mostly empty space
What was wrong with with Rutherford’s theory?
If the electrons were in a cloud around the nucleus, they would be attracted to its positive charge and the atom would collapse.
Which model of the atom did Niels Bohr adapt?
The nuclear model, he came up with the Bohr model
How did Niels Bohr adapt the nuclear model
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations.
What was later discovered about the positive charge of the nucleus?
Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles.
What didn’t the discovery of the proton explain?
The difference in the atomic mass and atomic number
How many years was the neutron an accepted scientific idea before it was actually discovered?
This was about 20 years after the nucleus became an accepted scientific idea until it was actually proven.
Who’s experimental work proved the existence of the neutron?
James Chadwick
What is the radius of an atom?
1 x 10 ^-10 m
