History of the atom

What was the atomic theory?

idea that everything is made of tiny little particles which can't be broken down any further

what are these tiny particles separated by in atomic theory?

empty space

who originally proposed atomic theory?

a guy from ancient greece called Democritus(500B.C.)

what did James Chadwich discover?

discovered there are neutral particles in nucleus as well(1932)

What did JJ. Thompson propose?

he proposed that the atoms was a general ball of positive charge with discrete electrons in it

What was JJ Thompson's model called?

plum pudding model(1897)

What did the plum pudding model show which we now know is wrong? ( 4 things)

showed that the mass of the atom is spread out

presented the atom as not mostly being empty space

the positive charge is spread out, not contained within a nucleus

the electrons not orbitting the nucleus in shells

What did Niels Bohr do?

adapted the nuclear model by suggesting electrons orbit the nucleus and also that they were held in shells

What did John Dalton suggest?

suggested atoms are solid spheres nd different types of spheres make up different elements(1803)

what was the alpha particle scattering experiment

- Rutherford and his student took positively charged alpha particles and fired it at a really thin piece of gold

- His hypothesis was that if positive charge in gold atoms was spread out as JJ Thompson proposed then it should pass right through the sheet of gold

- most of the alpha particles went straight through but some were deflected showing that the atom is mostly empty space

what did rutherford conclude after the alpha particle experiment and what model did he propose

Rutherford then suggested his nuclear model which proposed that instead of a general field of positive charge there was some sort of nucleus which contained all the positive charge of the atom

and most of the atom is empty space as most passed straight through

Rutherford also thought negative charge must exist in some sort of cloud around the nucleus this lead to the nuclear model

What was the flaw in Rutherford's model?

there wasn't anything stopping this cloud of negative electrons from rushing in towards the positive nucleus meaning the atom should automatically collapse which we know it doesn't

What did Rutherford conclude from his experiments?

- atoms are mainly empty space

- mass of atom is concentrated at the centre/nucleus

- there is a positive nucleus that deflects the positively charged alpha particle(1910)

Why was Niels Bohr's idea so important?

because orbiting of electrons in shells prevents atoms from collapsing due to electrons rushing in to positive centre

what is an alpha particle composed of?

2 protons and 2 electrons the same as helium nucleus