1
Q
What did John Dalton do?
A
- 19th century
- described atoms as solid sphere, and different spheres make different elements
2
Q
What did J J Thomson do?
A
- 1897
- concluding from his experiments that atoms weren’t solid spheres
- his measurements of charge and mass showed that atoms must contain even smaller, negatively charged particles (electrons)
- the theory was known as ‘plum pudding model’
3
Q
What did Ernest Rutherford do?
A
- 1909
- conducted famous gold foil experiment, firing positively charges particles at an extremely thin sheet of gold
- expecting most particles to be deflected by positive ‘pudding’ that made up most of the atom
- most particles passed straight through the gold atoms, very few deflected
- he came up with a theory to explain this (theory of the nuclear atom)
- tiny positively charged nucleus at the centre, surrounded by a cloud of negative electrons (most of the atom is empty space
4
Q
What did Niels Bohr do?
A
- suggested electrons exist only in fixed orbits, or shells, and not everywhere in between
- each shell has a fixed energy
- his theory was supported by many experiments and helped to explain many other scientists observations at the time
5
Q
How do scientists back up their theories with evidence?
A
- scientists do more experiments, get new evidence
- nearly always leading to scientific knowledge developing (new evidence prompts people to come up with new, improved ideas)
- these ideas can be used to make predictions, if proved right are good indication that the ideas are right
- scientists put their ideas and research up for peer review (everyone gets to see new ideas, check for errors and then use it to develop their own work)
6
Q
What are the properties of an atoms nucleus?
A
- middle of atom
- protons and neutrons
- positive charge because of protons
- almost the whole mass of electron is concentrate in the nucleus
7
Q
What are the properties of electrons?
A
- move around nucleus in electron shells
- negatively charged
- tiny, but cover lots of space
- volume of orbit determines size of atom
- virtually no mass
8
Q
What is the relation between protons and electrons?
A
- number of protons equals number of electrons
- the charge of electrons is the same as the charge of protons but opposite, so cancel each other out
- making a neutral atom
9
Q
What is scientists realise about Rutherford’s model?
A
-the cloud of electrons around the nucleus of the atom would be attracted to the nucleus and cause the atom to collapse
10
Q
What are the properties of electrons, neutrons and protons?
A
- protons are heavy and positively charged
- neutrons are heavy and neutral
- electrons are tiny and negatively charged
