1.2 History of the atom

chemistry topic 1

who first suggested matter is made of indivisible atoms

democritus

summarise john daltons theory

• described atoms as solid spheres

• different sized spheres make up different elements

who proposed that atoms are solid spheres

john dalton

who discovered electrons

j.j thompson

summarise jj thompsons findings and resulting theory

• atoms contain negatively charged particles (electrons)

• general ball of positive charge with discrete electrons inside

• plum pudding model

what was the plum pudding model and who proposed it

• proposed by j.j thompson

• atoms is a ball of positive charge with electrons inside it

who discovered the nucleus

ernest rutherford

summarise the experiment carried out by ernest rutherford

• cathode ray fired alpha particles at a thin gold sheet

summarise the results of the experiemnt carried out by ernest rutherford

found that some passed through but some bounced back showing small positively charged nucleus exists

what is the nuclear model and who proposed it

proposed by ernest rutherford

atoms have a small positively charged nucleus and the center is surround by a negative charge

what was the main issue with the nuclear model of an atom

the electrons should be attracted to the positive nucleus so the atom should collapse

who proposed electrons orbit the nucleus in fixed shells

neils bohr

what did james chadwick discover

neutral particles called neutrons inside the nucleus

who discovered protons

ernest rutherford

chronological order of diwcovery

1. democritus - atomic theory

2. john dalton - solid spheres

3. jj thompson plum pudding model

4. ernest rutherford - nuclear model

5. neils bohr - electron shells

6. ernest rutherford - protons

7. james chadwick - neutrons