Topic 4 - Atomic Structure

Question 1

In an atom what particles are equal

Answer 1

Protons and electrons

Question 2

Protons

Answer 2

Stay the same for each element and the number of them is called the atomic number

Question 3

Mass number

Answer 3

Protons + neutrons

Question 4

Isotopes

Answer 4

Atoms that have different numbers of neutrons

Question 5

Why do atoms turn into positive ions

Answer 5

When they lose electrons as electrons have a negative charge

Question 6

Plum Ludding

Answer 6

Positive charged ball with embedded electrons

Question 7

Alpha particle scattering experiment

Answer 7

They fired tiny alpha particles at gold foil a few atoms thick.
They saw most of the particles passed straight through the foil
Sometimes the particle was deflected as it passed through the foil
Sometimes the particle bounced straight back from the foil

Question 8

What did scientists conclude from the alpha particle experiment

Answer 8

1. Because most of the particles went straight through the foil, they are mostly empty space
2. Because some were deflected it meant the centre of the atom must have a positive charge which repelled the alpha particles
3. Because some bounced straight back the mass of the atom must be concentrated in the centre (the nucleus)

Question 9

Nuclear model

Answer 9

Mostly empty space, with a tiny positive charged nucleus in the middle and negative electrons around the edge.

Question 10

Radiation decay

Answer 10

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable.

Question 11

Activity

Answer 11

the rate at which a source of unstable nuclei decays

Question 12

Count-rate

Answer 12

The number of decays recorded each second by a detector

Question 13

An alpha particle

Answer 13

-Large mass
-Positive charge
-Two neutrons and two protons
-Very ionising due to large mass and charge
-Range in air is 3-5cm
-Is easily blocked by paper and skin
-Two protons two neutrons (same as helium nucleus)

Question 14

A beta particle

Answer 14

-Small mass
-Negative charge
-Quite ionising due to small mass and charge
-Less easily blocked, absorbed by thick aluminium and thin lead
-A high speed electron ejected from the nucleus as a neutron turns into a proton
-Range of air is tens of centimetres

Question 15

Gamma Ray

Answer 15

-No charge or mass
-Weakly ionising due to no mass or charge
-Electromagnetic radiation from the nucleus
-Air range is several metres
-Difficult to block, absorbed by thick lead, several metres of concrete.

Question 16

In a nuclear equation an alpha particle may be represented by what symbol

Answer 16

(4)
He
(2)

Question 17

In a nuclear equation an beta particle may be represented by what symbol

Answer 17

0
e
-1

Question 18

Half-life

Answer 18

The time it take for the number of nuclei of the isotope in a sample to halve

Question 19

what is the radius of an atom

Answer 19

1x10^-10

Question 20

Radius of the nucleus

Answer 20

less than 1/10,000 of the radius of the atom

Question 21

How do electrons move between energy levels

Answer 21

If they gain energ (e.g. absorb electromagnetic radiation) they transfer to the highest energy level as it’s furthest away from the nucleus, and if it loses energy it moves back to the lower level

Question 22

Relative mass of each particle types

Answer 22

proton - 1
neutron - 1
electron - 1/2000 (negligible)

Question 23

What was discovered about the atom in 1897

Answer 23

Atoms contain tiny negative particles showing particles are not spheres that cannot be divided, they have an internal

Question 24

What did Niels Bohr discover

Answer 24

electrons orbit the nucleus at specific distsnces

Question 25

What did James Chadwick discover

Answer 25

Particles with no charge that the nucleus contain

Question 26

20 years before Chadwicks discovery what did experiments show

Answer 26

The idea that the positive charge in a nucleus could be subdivided into particles called protons

Question 27

What is activity measured in

Answer 27

Becquerels
1 Bq = 1 decay per second

Question 28

How can you measure activity of a radio active source

Answer 28

Using a Geiger-Muller tube

Question 29

Why can’t scientists predict when a nucleus will decay

Answer 29

Decay is a random process

Question 30

Second definition for half life (count rate)

Answer 30

The time it takes for the count rate from a sample containing the isotope to fall to half its initial level

Question 31

Irradiation

Answer 31

Exposing an object to nuclear radiation

Question 32

Example of safe irradiation

Answer 32

-A syringe to be sterilised packaged in plastic to stop bacteria entering
-Placed by a radioactive isotope that’s behind a lead wall to protect workers
-Gamma radiation kills any bacteria present

Question 33

Why do irradiated objects not become radioactive

Question 34

risks of ionising radiation

Answer 34

-Can increase the risk of cancer

Question 35

How can you be shielded from the different types of radiation

Answer 35

-Alpha you can wear gloves
-Gamma and beta you need a lead apron

Question 36

Radioactive contamination

Answer 36

-When unwanted radioactive isotopes end up on other materials
-This is hazardous as the radioactive atoms decay and emit ionising radiation

Question 37

Alpha sources harm irradiation and contamination

Answer 37

-Less dangerous with irradiation as it can’t penetrate the skin and easily is blocked by a small air gap
-In the body alpha sources are most dangerous because they do their damage in a very localised area.

Question 38

Beta source harm irradiation and contamination

Answer 38

-Outside the body one of the most dangerous sources because they can get to the body and damage delicate organs
-Less damaging inside the body as radiation is absorbed over a wider area

Question 39

Gamma source harm irradiation and contamination

Answer 39

-Most dangerous outside the body as can penetrate body and get to delicate organs
-Least dangerous outside of the body as they mostly pass straight out and they have the lowest ionising power

Question 40

What is the nuclear equation for alpha particle

Answer 40

4
He
2

Question 41

What happens when a beta decay occurs

Answer 41

-A neutron in the nucleus turns into a proton and releases a fast-moving electron
-The nucleus’ positive charge increases
-Because the nucleus loses a neutron the mass doesn’t change as neutrons and protons have the same mass

Question 42

What is the nuclear equation of a beta particles

Answer 42

0
e
-1