Atomic Structure

Question 1

What is an Isotope?

Answer 1

> They are atoms with the same number of protons but different number of neutrons.

Question 2

What happens to unstable isotopes?

Answer 2

> They tend to decay into other elements and give out radiation as the try to become stable.(Radioactive Decay).

Question 3

How do we know if EM radiation is absorbed?

Answer 3

When electrons move to a higher orbit (further from the nucleus)

Question 4

How do we know if EM radiation is Emitted?

Answer 4

When the electrons falls to a lower orbit (closer to the nucleus)

Question 5

What happens if an electron gains enough energy

Answer 5

It can leave the atom to form a positive ion.

Question 6

What did Dalton propose?

Answer 6

Dalton said everything was made of tiny spheres (atoms) that could not be divided.

Question 7

What did JJ Thompson do?

Answer 7

> The overall charge of an atom is neutral, so
the negative electrons were dispersed
through the positive “pudding” to cancel
out the charges.

Question 8

What were the observations of the alpha particle scattering experiment?

Answer 8

Most 𝛼 particles went straight through:
->So most of atom is empty space

Some 𝛼 particles were slightly deflected:
>So nucleus must be charged, deflecting positive 𝛼

> Few 𝛼 particles were deflected by >90°:
- So nucleus contained most of the mass

Question 9

What did Rutherford Propose?

Answer 9

> There is a positive nucleus at the
centre of the atom, and negative electrons
existing in a cloud around the nucleus

Question 10

Later on what was introduced?

Answer 10

> Positive charge of nucleus could be subdivided into smaller particles, each with the same
amount of charge – the proton
->20 years after the ‘nucleus’ was an accepted scientific idea, James Chadwick provided
evidence to prove neutrons existed (don’t need specifics)

Question 11

What is radioactive decay?

Answer 11

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

Question 12

What is Alpha particles and its characteristics?

Answer 12

Alpha α (a helium nucleus)
 Highly ionising
 Weakly penetrating
(~5cm of air)

Question 13

What is Beta particles and its characteristics?

Answer 13

o Beta Minus β (electron)
 Medium ionising
 Medium penetration
(~50cm of air, sheet of paper)

Question 14

What is Gamma radiation and its characteristics?

Answer 14

Gamma γ (radiation)
 Low ionising
 Highly penetration
(very far in air, few cm of lead)

Question 15

What is the nuclear equation for Alpha Particle?

Answer 15

—4
A
2

Question 16

What is the nuclear equation for Beta Particle?

Answer 16

—0
B Not minus 0, but is -1.
-1

Question 17

Why don’t gamma rays change the charge of their nucleus?

Answer 17

> They have no charge.

Question 18

What is Half-Life

Answer 18

The half-life of an isotope is the time taken for half the nuclei in a sample to decay or the
time taken for the activity or count rate of a sample to decay by half.

Question 19

What happens in a short half life

Answer 19

o The source presents less of a risk, as it does not remain strongly radioactive
o This means initially it is very radioactive, but quickly dies down
o So presents less of a long-term risk

Question 20

What happens in a Long half-life

Answer 20

> The source remains weakly radioactive for a long period of time.
o It is suitable because it will not need to be replenished, and its weak activity means it won’t be harmful to anyone.

Question 21

Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous.

Answer 21

alpha radiation is highly ionising
causing an increased risk of cancer
until the radioactive material is removed / excreted

Question 22

Why is it safe to use a source of alpha radiation in a house?

Answer 22

beta and gamma radiation will penetrate smoke
no change (in the count rate) would be detected

Question 23

Explain the ideal properties of a radioactive source for use in medical diagnosis

Answer 23

alpha radiation is not very penetrating

Question 24

The smoke alarm would not work with a radiation source that emits beta or gamma radiation.
Explain why.

Answer 24

*   short half-life or half-life of a few hours
*   less damage to cells / tissues / organs body
*   low ionising power
*   less damage to cells / tissues / organs / body
*   highly penetrating
*   it can be detected outside the body
*   emits gamma radiation

Question 25

Explain how the paths of the alpha particles were used to develop the nuclear model of the
atom.

Answer 25

> Most alpha particles pass straight through the atom
Which shows that the atom is mostly empty space
Very few alpha particles are deflected through a large angle
Which shows the atom contains a nucleus where the mass / charge
of the atom is concentrated

Question 26

Niels Bohr adapted the nuclear model by suggesting electrons orbited the nucleus at specific distances.
Explain how the distance at which an electron orbits the nucleus may be changed.

Answer 26

> Electron may absorb electromagnetic radiation.
Move further from the nucleus.
To a higher energy level.

Question 27

What happens in contamination?

Answer 27

o Lasts for a long period of time
o The source of the radiation is transferred to an object

Question 28

What is Radioactive contamination

Answer 28

the unwanted presence of radioactive atoms
on other materials the hazard is the decaying of the contaminated atoms releasing radiation

Question 29

What is irradiation?

Answer 29

o Lasts only for a short period of time
o The source emits radiation, which reaches the object
o Medical items are irradiated sometimes to kill bacteria on its surface, but not to make the medical tools themselves radioactive

Question 30

Why do scientific research need to be peer reviewed?

Answer 30

• If they are on the effects of radiation on humans, peer review is essential
  o If initial studies got measurements wrong, safety levels based on the study may cause people to die.