C2 The History Of The Atom Flashcards
Name the 4 basic elements that Ancients Greeks thought made up everything
Earth
Air
Water
Fire
What did Leucippus and Democritus think made up the elements?
Atoms
A solid substance that could not be split into smaller units
How did John Dalton describe atoms?
As solid spheres
He also said that different spheres made up the different chemical elements we know today.
What did J J Thomson conclude from his experiments in 1904?
That atoms weren’t solid spheres.
His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons
What was J J Thomson’s theory known as?
The plum pudding model.
Give a brief outline of the plum pudding model.
The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it.
What were Ernest Rutherfords experiments of 1911 called?
Alpha scattering experiments.
What did the alpha scattering experiments consist of?
They fired positively charged alpha particles at an extremely thin sheet of gold.
If the plum pudding model was correct what did results did the alpha scattering experiments expect?
They were expecting the particles to pass straight through the sheet or to be slightly defected at most.
Why did Rutherford expect the particles to pass straight through the extremely thin sheet of gold?
The positive charge of each atom was thought to be very spread out through the pudding of the atom.
What did Rutherford find in the alpha scattering experiments?
Most of the particles did go straight through the gold sheet, but some were deflected more than expected and a small number were deflected backwards.
So the plum pudding model couldn’t be right.
What was the name of the model that Rutherford came up with as a result of the alpha scattering experiments?
The nuclear model of the atom.
Explain the nuclear model of the atom.
There’s a tiny, positively charged nucleus at the centre, surround by a ‘cloud’ of negative electrons - most of the atom is empty space.
Explain what happens to the alpha particles in the nuclear model.
When alpha particles came near the concentrated, positive charge of the nucleus, they were deflected.
If they were fired directly at the nucleus, they were deflected backwards.
Otherwise they passed through the empty space.
What was wrong with Rutherfords model?
Scientists realised tha electrons in a ‘cloud’ around the nucleus of an atom would be attracted to the nucleus, causing the atom to collapse.
