Topic 4: Atomic structure

What invented the atomic theory and what year?

Democritus in 500bc

What did John Dalton do in the 1800s

Used democritus ideas to describeatoms as solid spheres

What did jj Thompson do in 1897?

Come up with the plum pudding model using a series of experiments

What was the plum pudding model?

A model which proved atoms could not be a solid spheres and contained negatively charged particals.

What did jj Thompson find out with the plum pudding model

-Atoms were a general ball of positive charge

-atoms had discrete electrons

What did Rutherford do in 1909?

He shot alpha particles at a sheet of gold

How did Rutherford debunk jj Thompsons theory with this experiment?

• If the charge was spread out like jj Thompson said then the particles would pass right through but instead they deflected to the side or even back into the same direction proving jj Thompson theory wrong.

What was the nuclear model and who created it?

-a model created by Rutherford

-it showed that there was a nucleus containing positive charge and it was surrounded by negative.

What was a flaw of the nuclear model?

His models flaw was that he didn’t recognise the separation between the positive and negative charge meaning the negative could just collapse into the positive

What did Neils Bohr suggest in 1913?

-he suggested electrons orbit the nucleus preventing electrons to collapse and that they were holding shells

What are isotopes?

Isotopes are elements that have the same amount of protons but different amount of neutrons

What happens to some unstable isotopes?

-they can undergo decay into other elements

What is decay?

-decay is the causation of an unstable nuclei reducing the count rate

What is a count rate?

The number of decays recorded in seconds using a detector

What is ionisation?

When electrons absorb enough energy to leave the atom altogether.

Are all isotopes stable?

No some are unstable

What happens to unstable isotopes?

They undergo radioactive decay where they emit something in order to become stable

What is a radioactive material?

Material that consists of unstable isotopes that can decay

What are the 4 types or radiation?

-beta radiation

-aplpha radiation

-gamma radiation

-neutrons

Qualities of alpha particles?

-have two protons and two neutrons

-same nucleus as helium with an overall charge of 2+

-positive charge

Qualities of beta particles?

-one of the atoms neutrons decay into a proton and electron where the proton stays in the nucleus and the electron is emitted at high speed.

-overall charge of -1

Negative charge

Qualities of gamma particles?

-made of waves of electromagnetic radiation

-no mass or charge so can pass through materials

-no charge

-normally happens after beta or alpha radiation

How ionising and penetrative is alpha radiation?

Very ionising

Not very penetrative cannot travel far

Which two types of radiation can deflect by magnetic feild

Alpha and beta

Why does nothing speed up radioactive decay?

It is a random process that cannot be effected by external factors