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Physics > Unit 4 - The Atom & Decay > Flashcards

Unit 4 - The Atom & Decay Flashcards

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1
Q

Give an approximation for the radius of an atom.

A

1x10⁻¹⁰ metres

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2
Q

What are the three subatomic constituents of an
atom?

A
  1. Proton
  2. Neutron
  3. Electron
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3
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus.

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4
Q

Approximately what proportion of the total radius of
an atom is the radius of the nucleus?

A

1/10,000

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5
Q

Describe the arrangement of protons, neutrons and
electrons in an atom.

A

● The protons and neutrons are found in
the atom’s nucleus
● The electrons are found in discrete
energy levels around the nucleus

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6
Q

What type of charge does the nucleus of an atom
have? Why?

A

● Positive charge
● The nucleus contains protons and neutrons
● Protons have a positive charge
● Neutrons have no charge

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7
Q

Give two ways that an atom’s electron arrangement
can be changed.

A
  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
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8
Q

Explain how an atom’s electron arrangement
changes when it absorbs EM radiation.

A

● Electrons move further away from the
nucleus
● They move to a higher energy level

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9
Q

Explain how an atom’s electron arrangement
changes when it emits EM radiation.

A

● Electrons move closer to the nucleus
● They move to a lower energy level

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10
Q

How does the ratio of electrons to protons in an atom
result in the atom having no overall charge?

A

● The number of protons is equal to the
number of electrons
● Protons and electrons have equal and
opposite charges, so charge cancels

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11
Q

What do all forms of the same element have in
common?

A

They all have the same number of
protons.

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12
Q

What is the name given to the number of protons in
an atom?

A

Atomic Number

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13
Q

What is an atom’s mass number?

A

The total number of protons and
neutrons in the atom.

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14
Q

What is an isotope of an atom?

A

An atom of an element that has a
different number of neutrons, but the
same number of protons.

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15
Q

How do atoms turn into positive ions?

A

● They lose one or more of their outer
electrons
● Electrons are negatively charged, so
the resultant charge of the atom is
positive

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16
Q

What may lead to a scientific model being changed
or replaced?

A

The discovery of new experimental
evidence which doesn’t agree with the
existing theory.

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17
Q

How did the plum-pudding model describe the atom?

A

A ball of positive charge, with negatively
charged electrons distributed evenly
throughout it.

18
Q

Prior to the discovery of the electron, what was
believed about the atom?

A

The atom was believed to be indivisible.

19
Q

Which experiment led to the plum-pudding model
being discarded?

A

Rutherford’s alpha-scattering
experiment.

20
Q

What is the name given to the currently accepted
model of the atom?

A

The Bohr nuclear model.

21
Q

State the conclusions of the Alpha-Scattering
experiment.

A

● Most of the mass of the atom is
concentrated at the centre in the
nucleus
● The nucleus is positively charged

22
Q

What reinforces a scientific theory?

A

When experimental results agree with
the hypothesised theoretical calculations
and theories.

23
Q

What did James Chadwick’s experiments on the
atom prove?

A

The existence of neutrons.

24
Q

Why do unstable nuclei give out radiation?

A

● Unstable nuclei undergo decay to
become more stable
● As they release radiation their stability
increases

25
Q

What is the name of the process in which an
unstable nucleus gives out radiation to become more
stable?

A

Radioactive decay.

26
Q

Define the activity of an unstable nucleus.

A

Activity is the rate of decay of a source of
unstable nuclei.

27
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

28
Q

What is count-rate?

A

The number of radioactive decays per
second for a radioactive source.

29
Q

Give an example of a detector that may be used to
measure count-rate.

A

Geiger-Muller tube

30
Q

State four types of nuclear radiation.

A
  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
31
Q

What are the constituents of an alpha particle?

A

● Two protons and two neutrons
● It is the same as a helium nucleus

32
Q

What is the range of an alpha particle through air?

A

A few centimetres (normally in the range
of 2-10cm).

33
Q

What will stop beta radiation from passing through a
point?

A

● A thin sheet of aluminium
● Several metres of air

34
Q

What will stop gamma radiation from passing
through a point?

A

● Several centimetres of lead
● A few metres of concrete

35
Q

Which type of radiation is most ionising?

A

Alpha radiation.

36
Q

Which type of radiation is least ionising?

A

Gamma radiation.

37
Q

State any changes to mass or charge that occur due
to the emission of a gamma ray.

A

Both mass and charge remain
unchanged.

38
Q

Describe the nature of radioactive decay.

A

● Random
● Which nuclei decays and when is
determined only by chance
● It is impossible to predict which nuclei
will decay and when

39
Q

Define the half-life of a radioactive isotope.

A

● The time it takes for the number of
unstable nuclei in a substance to halve
● The time it takes for the count rate
from a sample to fall to half its initial
level

40
Q

What is radioactive contamination?

A

The presence of unwanted radioactive
nuclei on other materials.

41
Q

What is irradiation?

A

● The process of exposing a material to
nuclear radiation
● The material does not become
radioactive

42
Q

Why is it important for the results of studies on the
effects of radiation to be published and shared with
other scientists?

A

● To allow the findings to be
independently checked
● This is known as peer review

Physics (7 decks)

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