Atomic structure

What did john dalton propose?

Atoms were tiny spheres that couldn't be divided but they were made up of different atoms

What did J. J. Thomson propose?

Atoms where a ball of positive charge with tiny negative electrons embedded plum pudding model )

What did Rutherford do?

Alpha particle scattering experiment

• Fixed alpha particles at gold sheet that was only a few cells thick

• Most particles went straight through

• Some were deflected

• And some where deflected the way they came

What did the alpha scattering experiment prove?

• Most of the mass of the atom was concentrated in the center in a tiny nucleus

• This nucleus must have positive charge since it repelled the alpha particles

• Since most particles passed through most of an atom is empty space

What did Neils Bohr propose ?

Electrons orbit the nucleus in energy levels (shells)

What did James Chadwick do?

Proved the existence of a neutron

What is the radius of an atom ?

1 × 10(-1)

How many times smaller is the nucleus radius than the atom radius ?

10000x

What are isotopes?

Same number of protons and same atomic number but different numbers of neutrons ( a different mass number)

What do unstable isotopes do ?

Emit radiation to try and become more stable - radioactive decay

What are the types of ionising radiation that a nucleus will emit?

Alpha

Beta

Gamma

What are alpha particles?

• Two neutrons and two protons (helium nucleus)

What are beta particles?

Neutrons change into protons and electrons

• Beta particles are fast moving electrons that are released from the nucleus

• No mass and a charge of -1

What are gamma waves?

Electromagnetic waves with a short wavelength released by the nucleus

What are alpha particles air length and penetration potential?

• Can travel through air for 5cm before colliding with another air particle

• Is stopped by a thin sheet of paper

What are beta particles air length and what is it stopped by?

• Air length of 15cm

• Stopped by a few millimetres of aluminium

What is gamma waves air length and what is stoped by?

• Travel long distances in air

• Stopped by a few cm of lead

What is 1st 2nd and 3rd most ionising out of alpha beta and gamma particles?

1st -alpha

2nd - beta

3rd -gamma

What happens when an atom emits an alpha particle?

Atomic number reduces by 2

Mass number reduces by 4

(Because of 2 neutrons and 2 protons )

What happens when beta decay occurs?

Atomic number increases by 1

What do gamma rays do to the charge and mass of the nucleus?

nothing