AQA GCSE Combined Science: Trilogy · 6.4

Atomic structure

50 revision questions with answers for 6.4 Atomic structure in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.

All 50 questions and answers

Question 1 · Spec 6.4.1.1
Describe the basic structure of an atom.
Answer:
A small positive nucleus containing protons and neutrons, surrounded by negatively charged electrons in energy levels.
Question 2 · Spec 6.4.1.1
Where is most atomic mass, and how small is that region?
Answer:
In the nucleus, whose radius is less than about 1/10,000 of the atom's radius.
Question 3 · Spec 6.4.1.1
What is the approximate radius of an atom?
Answer:
About 1 × 10⁻¹⁰ m.
Question 4 · Spec 6.4.1.1
What can happen when an electron absorbs electromagnetic radiation?
Answer:
It can move to a higher energy level farther from the nucleus.
Question 5 · Spec 6.4.1.1
What happens when an electron falls to a lower energy level?
Answer:
It emits electromagnetic radiation as energy is transferred away.
Question 6 · Spec 6.4.1.2
How does an atom become a positive ion?
Answer:
It loses one or more outer electrons, leaving more protons than electrons.
Question 7 · Spec 6.4.1.2
What is atomic number?
Answer:
The number of protons in the nucleus, which identifies the element.
Question 8 · Spec 6.4.1.2
What is mass number?
Answer:
The number of protons plus neutrons in the nucleus.
Question 9 · Spec 6.4.1.2
A neutral atom has atomic number 6 and mass number 14. Count its particles.
Answer:
6 protons, 8 neutrons and 6 electrons.
Question 10 · Spec 6.4.1.2
What are isotopes?
Answer:
Atoms of the same element with equal proton numbers but different neutron numbers.
Question 11 · Spec 6.4.1.2
For a nucleus written with mass number A and atomic number Z, how many neutrons are present?
Answer:
A - Z.
Question 12 · Spec 6.4.1.3
Why was the indivisible-sphere atomic model replaced?
Answer:
Discovery of electrons showed that atoms contain smaller particles.
Question 13 · Spec 6.4.1.3
What did the plum pudding model propose?
Answer:
A spread-out region of positive charge containing embedded negative electrons.
Question 14 · Spec 6.4.1.3
What did most alpha particles do in the thin-foil scattering experiment?
Answer:
They passed straight through or were only slightly deflected.
Question 15 · Spec 6.4.1.3
What did the passage of most alpha particles reveal?
Answer:
Most of the atom is empty space.
Question 16 · Spec 6.4.1.3
What did the very large deflections reveal?
Answer:
A tiny, dense, positively charged nucleus contains most of the atom's mass.
Question 17 · Spec 6.4.1.3
What were Bohr's and Chadwick's contributions?
Answer:
Bohr proposed specific electron energy levels; Chadwick provided evidence for neutrons in the nucleus.
Question 18 · Spec 6.4.2.1
Why do some nuclei emit nuclear radiation?
Answer:
They are unstable and decay to become more stable.
Question 19 · Spec 6.4.2.1
What does random radioactive decay mean?
Answer:
It is impossible to predict exactly when a particular unstable nucleus will decay.
Question 20 · Spec 6.4.2.1
Define activity.
Answer:
The number of nuclear decays occurring in a source per second.
Question 21 · Spec 6.4.2.1
What does an activity of 500 Bq mean?
Answer:
The source undergoes an average of 500 decays per second.
Question 22 · Spec 6.4.2.1
What does a Geiger-Muller detector measure?
Answer:
Radiation detected as counts, often recorded as a count rate.
Question 23 · Spec 6.4.2.1
Why can detector count rate be lower than source activity?
Answer:
The detector may collect only some emissions because of distance, direction, absorption and detector efficiency.
Question 24 · Spec 6.4.2.1
What is an alpha particle?
Answer:
Two protons and two neutrons: the same as a helium nucleus, with charge +2.
Question 25 · Spec 6.4.2.1
What is beta-minus radiation?
Answer:
Fast electrons emitted from the nucleus when neutrons change into protons.
Question 26 · Spec 6.4.2.1
What is gamma radiation?
Answer:
Electromagnetic radiation emitted from the nucleus; it has no mass or electric charge.
Question 27 · Spec 6.4.2.1
Which uncharged nuclear particle can also be emitted in nuclear processes?
Answer:
A neutron.
Question 28 · Spec 6.4.2.1
Compare the penetration of alpha, beta and gamma radiation.
Answer:
Alpha is stopped by paper; beta by thin aluminium; gamma is reduced by thick lead or concrete.
Question 29 · Spec 6.4.2.1
Compare their typical ranges in air.
Answer:
Alpha travels only a few centimetres, beta farther, and gamma has a much longer range.
Question 30 · Spec 6.4.2.1
Compare their ionising powers.
Answer:
Alpha is strongly ionising, beta moderately ionising and gamma weakly ionising compared with alpha and beta.
Question 31 · Spec 6.4.2.1
A thickness gauge needs radiation partly absorbed by thin metal foil. Why might beta be suitable?
Answer:
Alpha would be fully absorbed and gamma mostly transmitted; beta absorption can vary detectably with foil thickness.
Question 32 · Spec 6.4.2.1
Why is an alpha source especially hazardous if swallowed or inhaled?
Answer:
Its strongly ionising radiation transfers energy over a short distance inside living tissue.
Question 33 · Spec 6.4.2.2
How does alpha decay change mass number and atomic number?
Answer:
Mass number decreases by 4; atomic number decreases by 2.
Question 34 · Spec 6.4.2.2
How does beta-minus decay change mass number and atomic number?
Answer:
Mass number stays the same; atomic number increases by 1.
Question 35 · Spec 6.4.2.2
How does gamma emission change mass number and atomic number?
Answer:
Neither changes; the nucleus loses energy.
Question 36 · Spec 6.4.2.2
A nucleus with A = 238 and Z = 92 emits alpha. Find the daughter's A and Z.
Answer:
A = 234 and Z = 90. The emitted alpha particle accounts for the missing 4 and 2.
Question 37 · Spec 6.4.2.2
A nucleus with A = 14 and Z = 6 emits beta-minus. Find the daughter's A and Z.
Answer:
A = 14 and Z = 7; the beta particle has mass number 0 and charge number -1.
Question 38 · Spec 6.4.2.2
Why does beta-minus decay not change the nucleus's mass number?
Answer:
One neutron becomes one proton, so the total number of protons plus neutrons stays the same.
Question 39 · Spec 6.4.2.3
Define half-life.
Answer:
The time for the number of undecayed nuclei, activity or corrected count rate of an isotope to halve.
Question 40 · Spec 6.4.2.3
How is half-life found from an activity-time graph?
Answer:
Choose an activity value, find when it falls to half that value and measure the time interval.
Question 41 · Spec 6.4.2.3
Activity falls from 800 to 400 Bq in 6 hours. Find the half-life.
Answer:
6 hours, because the activity has halved.
Question 42 · Spec 6.4.2.3 · Higher only
What fraction of the original activity remains after three half-lives?
Answer:
1/2³ = 1/8, or 12.5%.
Question 43 · Spec 6.4.2.3 · Higher only
What fraction of the original emission has declined after four half-lives?
Answer:
1/16 remains, so the decline is 15/16, or 93.75%.
Question 44 · Spec 6.4.2.3
Measured count falls from 600 to 320 counts/min with background 40 counts/min in 5 min. Find half-life.
Answer:
Corrected counts fall from 560 to 280 counts/min, so the half-life is 5 min.
Question 45 · Spec 6.4.2.3
Why can half-life predict a large sample's behaviour but not one nucleus's decay time?
Answer:
Individual decays are random, but large numbers show a predictable statistical decrease.
Question 46 · Spec 6.4.2.4
What is radioactive contamination?
Answer:
Unwanted radioactive material on or inside another material or organism.
Question 47 · Spec 6.4.2.4
What is irradiation, and does it normally make the object radioactive?
Answer:
Exposure to nuclear radiation. The exposed object does not become radioactive merely because it is irradiated.
Question 48 · Spec 6.4.2.4
Why can contamination continue to cause exposure after leaving a source area?
Answer:
Radioactive material remains on or inside the person and continues to decay.
Question 49 · Spec 6.4.2.4
How can exposure to a radioactive source be reduced?
Answer:
Minimise time near it, increase distance and use suitable shielding and handling equipment; prevent contamination.
Question 50 · Spec 6.4.2.4
Why should studies of radiation effects be shared and peer-reviewed?
Answer:
Other scientists can check methods and conclusions, strengthening the evidence used to assess risks.

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