C4a

Question 1

What did John Dalton do?

Answer 1

• 19th century

- described atoms as solid sphere, and different spheres make different elements

Question 2

What did J J Thomson do?

Answer 2

• 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’

Question 3

What did Ernest Rutherford do?

Answer 3

• 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

Question 4

What did Niels Bohr do?

Answer 4

• 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

Question 5

How do scientists back up their theories with evidence?

Answer 5

• 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)

Question 6

What are the properties of an atoms nucleus?

Answer 6

• middle of atom
• protons and neutrons
• positive charge because of protons
• almost the whole mass of electron is concentrate in the nucleus

Question 7

What are the properties of electrons?

Answer 7

• move around nucleus in electron shells
• negatively charged
• tiny, but cover lots of space
• volume of orbit determines size of atom
• virtually no mass

Question 8

What is the relation between protons and electrons?

Answer 8

• 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

Question 9

What is scientists realise about Rutherford’s model?

Answer 9

-the cloud of electrons around the nucleus of the atom would be attracted to the nucleus and cause the atom to collapse

Question 10

What are the properties of electrons, neutrons and protons?

Answer 10

• protons are heavy and positively charged
• neutrons are heavy and neutral
• electrons are tiny and negatively charged