C1 - History Of The Atom

Question 1

At the start of the 19th century what did John Dalton say about atoms?

Answer 1

He said the atoms were solid spheres and said that the different spheres made up different elements

Question 2

In 1897,what did JJ Thompson conclude from his experiments?

Answer 2

Atoms werent solid spheres.

(His measurements of charge and mass showed that an atom must contain even smaller,negatively charged particles - ectrons.The ‘solid sphere’ idea of the atomic structure had to be changed.The new theory was known as the ‘plum pudding model)

(The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it)

Question 3

What happened in 1909 with Ernest Rutherford and his student Ernest Mardsen?

Answer 3

They conducted the famous alpha particle scattering experiments.They fired positively charged alpha particles at an extremely thin sheet of gold.From the plum pudding model,they were expecting the particles to pass straight through the sheet or be slightly deflected at most.This was because the positive charge of each atom was though to be very spread out through the pudding of the atom.But,whilst most of the particles did go straight through the sheet,some were deflected more than expected,and a small number were deflected backwards.So the plum pudding model couldnt be right.

Question 4

What did Rutherford come up with after the experiment?

Answer 4

The nuclear model of the atom.In this a tiny,positive charged nucleus at the centre,where most of the mass is concentrated.A ‘cloud’ of negative electrons surrounds this nucleus - so most of the atom is empty space.

(When alpha particles came near the concentrated,positive charge of the nucleus they were deflected.If they were fired directly at thr nucleus.They were deflected backwards.Otherwise,they passed through the empty space)

Question 5

In 1913 what did Niels Bohr discover?

Answer 5

• All electrons were contained in shells
• Bohr proposed that electrons orbit the nucleus in fixed shells and arent anywhere in between
• Each shell is a fixed distance from the nucleus

(Bohrs theory of the atomic structure was supported by many experiments and it helped explain lots of other scientists observations at the time)

Question 6

In 1932,what did James Chadwick discover?

Answer 6

James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.The discovery of neutrons resulted in a model of the atom which was pretty close to the modern day accepted version,known as the nuclear model

(Protons were also discovered by another person)