Topic 4 - Developing the Model of the Atom

Question 1

Who was John Dalton and what year did he come up with his theory?

Answer 1

John Dalton agreed with Democritus in 1804 that atoms were tiny spheres that couldn’t be destroyed, but every element had a unique sphere.

Question 2

What model did J.J Thompson introduce 100 years after John Dalton?

Answer 2

The ‘plum pudding’ model that suggested that they were spheres of positive charge with small negatively charged electrons stuck inside them (after he discovered the electron).

Question 3

Describe the alpha scattering experiment. Who carried it out and in what year?

Answer 3

In 1909, scientists in Rutherford’s lab fired alpha particles at thin gold foil. If the plum pudding model was correct, all the particles would pass through the sheet. However, whilst most did, some were deflected and a few were deflected straight back, disproving the model.

Question 4

What did the alpha scattering experiment prove?

Answer 4

It proved that most of the mass of the atom was in the centre - the nucleus. Since it repelled positive particles, it must be positive. It must have been mostly empty space since most particles passed through.

Question 5

What is our model of the atom called?

Answer 5

The nuclear model.

Question 6

What did Niel Bohr achieve?

Answer 6

He stated that the electrons orbited at certain distances called energy levels, which correlated with experimental data.

Question 7

When and who proved the neutron existed?

Answer 7

James Chadwick in 1932.

Question 8

Describe the current model of the atom. 
Nucleus?
Radius?
Electrons?
Charge?
EM?

Answer 8

The nucleus makes up most of the mass. It contains positive protons (+1) and neutral neutrons (+-0). It’s radius is 10 000 x smaller than the radius of the atom.
Negative (-1) electrons orbit the nucleus in the empty space around it.
The radius of the atom is 10x10(-10) m.
Atoms have no overall charge.
Electrons can move closer to the nucleus by releasing EM radiation and can move further away by absorbing EM radiation. If one or more outer electrons leave the atom it becomes positive.

Question 9

What is an isotope?

Answer 9

An isotope is an atom with the same number of protons as its element, but it has a different number of neutrons.

Question 10

What do unstable isotopes do to become stable?

Answer 10

The process is called radioactive decay, as they decay into different elements and give out radiation to become stable.

Question 11

What are the 3 radioactive ionising radiation particles?

Answer 11

Alpha, gamma and beta particles.

Question 12

What is an alpha particle? What element is it similar to? How many protons and neutrons is it made from?

Answer 12

It is like a helium nucleus made of 2 neutrons and 2 protons.

Question 13

How far do alpha particles travel through air? What can they be stopped by?

Answer 13

They travel a few cm few are and can be stopped by a sheet of paper.

Question 14

Why are alpha particles strongly ionising?

Answer 14

Because of their size.

Question 15

Where are alpha, gamma and beta particles released from?

Answer 15

The nucleus.

Question 16

What is a beta particle? What is it made from? Complete the sentence - for every beta particle emitted, a —– from the nucleus has turned into a —–. How far does it travel and what can stop it?

Answer 16

A beta particle is a high speed particle which is an electron with a negative charge. ‘Neutron’ and ‘proton’. They can travel a few metres and can be stopped by a sheet of aluminium.

Question 17

How ionising is a beta particle?

Answer 17

Moderately.

Question 18

What are gamma rays? How far do they travel and how can they be stopped? Why do they do more damage?

Answer 18

Gamma rays are electromagnetic radiation waves that can travel a long distance. They can be stopped by thick lead or metres of concrete. They are damaging because they are weakly ionising but can penetrate far into materials and once they hit something they do damage.

Question 19

What do nuclear equations show? How are they written? What do you have to remember about nuclear equations?

Answer 19

Nuclear equations show radioactive decay using elemental symbols. They’re written in the form ‘atom before decay – atom after decay + radiation emitted’. You have to remember that the total mass and atomic numbers must be equal on both sides.

Question 20

When an alpha particle leaves a nucleus, what does the mass and atomic number decrease by?

Answer 20

The atomic number decreases by 2 and the mass reduces by 4.

Question 21

When an alpha particle is released, does the charge increase or decrease and why?

Answer 21

It decreases because 2 protons and neutrons leave the nucleus, taking the positive charge and reducing the overall charge.

Question 22

When beta radiation is released, does the mass change and why?

Answer 22

It doesn’t change because the nucleus loses a proton and gains a neutron.

Question 23

When beta radiation is released, does the charge become positive or negative and why?

Answer 23

The charge becomes positive because a neutron in a nucleus becomes a proton and releases the fast electron (beta), which increases the charge of the nucleus.

Question 24

Does gamma radiation change anything about the atom and why?

Answer 24

Gamma changes nothing because it is simply a way of releasing excess energy as an EM wave.

Question 25

How is radioactive decay measured and is radioactive decay random or ordered?

Answer 25

It is measured using a Geiger-Muller tube, which measures the count rate, or radiation count reaching it per second, and counter and it is a completely random process.

Question 26

What is a half-life and how is it measured?

Answer 26

The half-life is the predicted time that it takes for a substance to half decay. It is called activity and is measured in Bq, or becquerels, which is an amount of decay per second.

Question 27

Why are sources with a shorter half-life more dangerous?

Answer 27

Because they are much more unstable and are more likely to give out a lot of harmful radiation.

Question 28

Why can substances with a longer half-life be dangerous?

Answer 28

Because areas can be exposed to radiation for millions of years.

Question 29

Define half-life.

Answer 29

The amount of time it takes for radioactive nuclei in an isotope to halve.

Question 30

When plotting a half-life graph, what always goes on the x-axis and y-axis?

Answer 30

The x-axis is time.

The y-axis is radioactive decay or ACTIVITY in Bq.

Question 31

What is background radiation?

Answer 31

The radiation that is always around us.

Question 32

What are the 3 sources of background radiation?

Answer 32

1) Natural unstable isotopes found in atoms such as in rocks or food.
2) Radiation from space, called cosmic rays. The atmosphere protects us from most of these.
3) Radiation from human activity.

Question 33

What is irradiation?

Answer 33

When an object is exposed to radiation. It doesn’t make an object radioactive.

Question 34

How can you stop us from being irradiated?

Answer 34

Putting objects in a box lined with lead, standing behind a barrier and being in a different room and using robots to handle them.

Question 35

What is contamination and why is it dangerous?

Answer 35

It is when unwanted radioactive particles get into an object. It’s dangerous because the particles can still decay and they could get into your body and harm you.

Question 36

How can we avoid being contaminated?

Answer 36

We can use gloves and tongs to handle radioactive objects.

Question 37

Outside of the body, which are the most dangerous sources of radiation and why?

Answer 37

Gamma and beta because they can get past your skin and damage your organs. Alpha can’t get past the skin.

Question 38

Inside the body, which is the most dangerous radioactive source and why? Why are the others less dangerous?

Answer 38

Alpha particles are the most dangerous because they can do damage in a localised area. Beta particles do less damage over a larger area and gamma rays are the least ionising so they just pass out of the body.

Question 39

What are the risks of using lower and higher diesel of radiation?

Answer 39

1) Lower doses tend to cause minor damage, creating uncontrollable mutant cells (cancer).
2) Higher doses kill cells, causing radiation damage.
Both doses cause tissue damage because the radiation gets into the cells and ionises the atoms and molecules.

Question 40

How are gamma rays used medically? Describe it in detail, giving the names of elements.

Answer 40

Gamma rays are used as medical tracers. They are injected or swallowed and a tracer follows it around the body, creating an image of where the radiation is strongest. An example of an isotope used is iodine 123 because it is taken in by the thyroid and shows if the thyroid is taking in iodine 127 as it should. The weak ionising nature means the rays pass out of the body quickly without harming the patient.

Question 41

How are gamma rays used against cancer?

Answer 41

Gamma rays are fired at cancerous cells during radiotherapy, or are placed as implants next to cancerous cells inside the body. The right dose needs to be given in the right place to avoid killing lots of normal cells. This can make the patient feel very unwell.

Question 42

What is nuclear fission?

Answer 42

It is the process of splitting unstable and large isotopes such as plutonium and uranium into smaller atoms.

Question 43

Describe how fission occurs.

Answer 43

The isotope absorbs a neutron and the isotope splits into smaller atoms, releasing 3 more neutrons. If these get absorbed by other isotopes this starts a chain reaction. This releases kinetic energy. Any energy that isn’t kinetic is released as gamma.

Question 44

How can the gamma and kinetic energy released by fission be used?

Answer 44

It can be used to turn turbines to generate electricity.

Question 45

How is released energy controlled during fission and what happens if lots of this energy is released?

Answer 45

It is controlled using control rods that absorb neutrons and which change how quickly the chain reaction can happen. If too much energy is released too fast, a nuclear explosion happens like in Chernobyl or in a nuclear weapon.

Question 46

How does nuclear fusion occur?

Answer 46

Nuclear fusion occurs when light nuclei collide at high speed to create a larger atom. Not all of the mass is kept - some is converted to energy released as radiation.

Question 47

How is the energy from nuclear fusion used?

Answer 47

The energy from fusion is far greater than the energy from fission but scientists don’t know how to use it yet commercially because the conditions for a nuclear fusion (temperature and pressure) make building fusion reactors difficult and expensive.