Topic Four - Atomic Structure

Question 1

What did John Dalton believe about the atom?

Answer 1

In 1804 hes said that matter was made up of tiny spheres that couldnt be broken up and each element was made up of a different type of atom.

Question 2

What did JJ Thompson say about the atom?

Answer 2

He discovered electrons that could be removed from atoms.
Thompson suggedted atoms were spheres of positive charge with tiny negative electrons stuck in them - the plum pudding model.

Question 3

What did Rutherford say about the atom?

Answer 3

He fired a beam of alpha particles at thin gold foil - alpha scattering experiment. From the plum pudding model they expected the particles to pass through the gold sheet, or only be slightly deflected.
Most particles went straight theough the sheet, but some were deflected back the way they came.
This was because most of the mass was concentrated at the tiny nucleus. The nucleus must have a positive chanrge as it repelled the alpha particles.
Also most of the atom is empty space as most alpha particles passed straight through.

Question 4

What did Bohr say about the atom?

Answer 4

Said electrons orbiting the nucleus did so at certain distances called energy levels. His calculations agreed with experimental data.
The nucleus had a geoup of protons which all had the same positive charge thay added up the the overall charge of the nucleus.

Question 5

What did James Chadwick say about the atom?

Answer 5

Proved the existance of the neuron which explained the imbalance between the atomic and mass numbers.

Question 6

What is the current model of the atom?

Answer 6

The nucleus makes up most of the mass of the atom. It contains protons which are positively charged and neutrons which are neutral which gives an overall positive charge.
Radius is around 10000 times smaller than the radius of the atom.
The rest of the atom is empty space.
Negative elctrons go around the outside of the nucleus really fast.

Question 7

What happens to electrons if they gain energy by absorbing EM radiation?

Answer 7

They move to a higher energy level further from the nucleus.

Question 8

What happens if electrons release EM radiation?

Answer 8

They move to a lower energy level that is closer to the nucleus.

Question 9

What is the atomic number?

Answer 9

Number of protons in an atom.

Question 10

What is the mass number?

Answer 10

Number of protons + the number of neutrons in its nucleus.

Question 11

What are isotopes?

Answer 11

An element with the same number of protons but a different number of neutrons.

Question 12

What happens to unstable isotopes?

Answer 12

They tend to decay into other elements and give out radiation as they try to become more stable. This is called radioactive decay.

Question 13

What is ionising radiation?

Answer 13

Radiation which knocks electrons off atoms creating positive ions. The ionising power of a radiation source is how easily it can do this.

Question 14

What is an alpha particle?

Answer 14

A helium nuclei.

Question 15

What is alpha radiation?

Answer 15

It is when a alpha particle is emitted from the nucleus ( two neutrons and two protons)
They dont penetrate very fat they can only travel a few cm and are absorbed by a sheet of paper.

Question 16

What is alpha radiation used in?

Answer 16

Smok detectors - it ionises air particles causing a current to flow. If there is smoke in the air it binds to the ions meaning the current stops and the alarm goes off.

Question 17

What is a beta particle?

Answer 17

A fast moving electron released from the nucleus.

Question 18

What is beta radiation?

Answer 18

It is moderately ionising and can penetrate moderately far into materals before colliding and has a range of a few metres. They can be absorbed by a sheet of aluminium.
For every beta particle emitted a neutron has to be turned into a proton.

Question 19

What are beta particles used for?

Answer 19

Beta emitters - tests the thickness of sheets of metal as they are nit immediately absorbed like alpha but dont penetrate as fat as gamma. Therefore slight variations in thickness affect the amount of radiation passing theough the sheet.

Question 20

What is a gamma ray?

Answer 20

Waves of electromagnetic radiation released by the nucleus.

Question 21

What do gamma rays do?

Answer 21

They penetrate far into materials eithout being stopped and can travel long distances through air. Only weakly ionising as they tend to pass through rather than colliding with atoms. Eventually theyhit something and do damages.
They can be absorbed by thick sheets of lead or concrete.

Question 22

What are nuclear equations?

Answer 22

They show radioactive decay by using element symbols.

Question 23

Why do gamma rays not change the charge or mass of the nucleus?

Answer 23

They are a way of getting rid of excess energy from a nucleus.
So there is no change to the atomic mass or atomic number of the atom.

Question 24

How can radiation be measured?

Answer 24

A Geiger-Muller tube and counter which records the count rate ( the number of radiation counts reaching it per second ).

Question 25

How can yoy find out how long it takes for the amount of radiation emitted by a source to halve?

Answer 25

You use a half life which is used to make predictions on radioactive sources and find the rate at which the source decays ( its activity ).

Question 26

What is half life??

Answer 26

The time taken for the number of radioactive nuclei in an isotope to halve.

Question 27

What are risks to radiation?

Answer 27

Ionising radiation can enter living cells and ionise atoms within them. This can damage cells and cause cancer or completely kill the cell.

Question 28

What is irridation?

Answer 28

Objects near a radioactive source are irridated by it meaning they are always exposed to it. It does not make it radioactive.

Question 29

How can you reduce irridation?

Answer 29

Keeping sources in lead lined boxes or standing behind barriers in different rooms. Also using remote controlled atms when working with radioactive sources.

Question 30

How is contamination dangerous?

Answer 30

If you touch a radioactive source without gloves on your hands would be contaminated. The contaminating atoms may then decay which releases radiation causing you hands. The radioactive particles may enter your body.

Question 31

How can you prevent contamination?

Answer 31

Gloves and tongs used when handling sources to stop particles getting stuck to your skin or under your nails. Also protective suits to stop breathing in particles.

Question 32

What is the most dangerous radiation type for irridation?

Answer 32

Outside the body beta and gamma are the most dangerous as they can penetrate the body and get to delicate organs.
High levels of irridation from all sources are dangerous but especially ones that emit beta and gamma.

Question 33

What is the least dangerous radiation type for irridation?

Answer 33

Alpha as it cant penetrate the skin and is easily blocked by a small air gap.

Question 34

What is the most dangerous radiation type for contamination?

Answer 34

Inside the body alpha sources are the most dangerous as they do damage in a localised area. So contamination is a major concern when working with alpha sources.

Question 35

Which radiation types are less dangerous for contamination?

Answer 35

Beta is less damaging as radiation is absorbed over a wider are and some passes out the body altogether.
Gamma sources are the least dangerous jn the body as they mostly pass straight out, they have the lowest ionising power.