Atomic structure
50 exam-style questions with answers for 4.4 Atomic structure in AQA GCSE Physics (spec 8463). 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 4.4.1.1 · Atoms
What is the approximate radius of an atom? [1 mark]
Answer:1 × 10⁻¹⁰ m.Question 2 · Spec 4.4.1.1 · Atoms
How does the radius of a nucleus compare with the radius of an atom? [1 mark]
Answer:It is less than 1/10 000 of the radius of the atom.Question 3 · Spec 4.4.1.1 · Atoms
Describe the structure of an atom. [2 marks]
Answer:A small, positively charged nucleus of protons and neutrons, containing almost all the mass (1); surrounded by negatively charged electrons (1).Question 4 · Spec 4.4.1.1 · Energy levels
What happens when an electron absorbs electromagnetic radiation? [1 mark]
Answer:It moves to a higher energy level, further from the nucleus.Question 5 · Spec 4.4.1.1 · Energy levels
What happens when an electron emits electromagnetic radiation? [1 mark]
Answer:It moves to a lower energy level, closer to the nucleus.Question 6 · Spec 4.4.1.2 · Atomic number
Why do atoms have no overall charge? [1 mark]
Answer:They have equal numbers of protons and electrons.Question 7 · Spec 4.4.1.2 · Isotopes
Define the term 'isotope'. [2 marks]
Answer:Atoms of the same element with the same number of protons (1); but different numbers of neutrons (1).Question 8 · Spec 4.4.1.2 · Mass number
How many neutrons are in an atom of carbon-14 (atomic number 6)? [1 mark]
Answer:14 − 6 = 8.Question 9 · Spec 4.4.1.2 · Ions
How does an atom become a positive ion? [1 mark]
Answer:It loses one or more outer electrons.Question 10 · Spec 4.4.1.3 · Atomic model
Describe the plum pudding model. [2 marks]
Answer:The atom was a ball of positive charge (1); with negative electrons embedded in it (1).Question 11 · Spec 4.4.1.3 · Atomic model
Describe the results of the alpha particle scattering experiment. [3 marks]
Answer:Most alpha particles passed straight through the gold foil (1); some were deflected by small angles (1); a very few bounced back (1).Question 12 · Spec 4.4.1.3 · Atomic model
What did the alpha scattering experiment show about atoms? [2 marks]
Answer:Most of the atom is empty space (1); the mass and positive charge are concentrated in a tiny nucleus (1).Question 13 · Spec 4.4.1.3 · Atomic model
What did Niels Bohr contribute to the model of the atom? [1 mark]
Answer:He suggested electrons orbit the nucleus at specific distances (energy levels), which agreed with experiments.Question 14 · Spec 4.4.1.3 · Atomic model
Who provided evidence for the neutron and when? [1 mark]
Answer:James Chadwick, about 20 years after the nucleus was accepted (1932).Question 15 · Spec 4.4.2.1 · Radioactive decay
What is radioactive decay? [1 mark]
Answer:The random process by which an unstable nucleus gives out radiation to become more stable.Question 16 · Spec 4.4.2.1 · Activity
Define activity and give its unit. [2 marks]
Answer:The rate at which a source of unstable nuclei decays (1); measured in becquerels (Bq) (1).Question 17 · Spec 4.4.2.1 · Count rate
What is count rate? [1 mark]
Answer:The number of decays recorded each second by a detector, such as a Geiger-Muller tube.Question 18 · Spec 4.4.2.1 · Alpha
What is an alpha particle? [1 mark]
Answer:Two neutrons and two protons (a helium nucleus).Question 19 · Spec 4.4.2.1 · Beta
What is a beta particle? [1 mark]
Answer:A high-speed electron ejected from the nucleus as a neutron turns into a proton.Question 20 · Spec 4.4.2.1 · Gamma
What is gamma radiation? [1 mark]
Answer:Electromagnetic radiation from the nucleus.Question 21 · Spec 4.4.2.1 · Penetration
Compare the penetrating power of alpha, beta and gamma. [3 marks]
Answer:Alpha is stopped by paper or a few cm of air (1); beta is stopped by a few mm of aluminium (1); gamma is reduced by thick lead or concrete (1).Question 22 · Spec 4.4.2.1 · Ionising power
Which type of radiation is most ionising? [1 mark]
Answer:Alpha.Question 23 · Spec 4.4.2.2 · Nuclear equations
What happens to the mass number and atomic number in alpha decay? [2 marks]
Answer:The mass number decreases by 4 (1); the atomic number decreases by 2 (1).Question 24 · Spec 4.4.2.2 · Nuclear equations
What happens to the mass number and atomic number in beta decay? [2 marks]
Answer:The mass number stays the same (1); the atomic number increases by 1 (1).Question 25 · Spec 4.4.2.2 · Nuclear equations
Radium-226 (atomic number 88) emits an alpha particle. What are the mass number and atomic number of the new nucleus? [2 marks]
Answer:Mass number 222 (1); atomic number 86 (radon) (1).Question 26 · Spec 4.4.2.2 · Nuclear equations
Why does gamma emission not change the mass or charge of the nucleus? [1 mark]
Answer:Gamma rays have no mass and no charge.Question 27 · Spec 4.4.2.3 · Half-life
Define half-life. [2 marks]
Answer:The time it takes for the number of nuclei of the isotope in a sample to halve (1); or the time for the count rate from a sample to fall to half its initial level (1).Question 28 · Spec 4.4.2.3 · Half-life
A sample has an activity of 800 Bq and a half-life of 2 days. What is its activity after 6 days? [2 marks]
Answer:6 days = 3 half-lives (1); 800 → 400 → 200 → 100 Bq (1).Question 29 · Spec 4.4.2.3 · Half-life · Higher only
A sample's count rate falls from 400 to 50 counts/s. Express the net decline as a ratio of the original. [2 marks]
Answer:400 → 200 → 100 → 50 is 3 half-lives (1); net decline = 350/400 = 7/8 (the remaining fraction is 1/8) (1).Question 30 · Spec 4.4.2.3 · Random decay
Why is radioactive decay described as random? [1 mark]
Answer:It is impossible to predict which nucleus will decay next or when.Question 31 · Spec 4.4.2.4 · Contamination
What is radioactive contamination? [1 mark]
Answer:The unwanted presence of materials containing radioactive atoms on or in other materials.Question 32 · Spec 4.4.2.4 · Irradiation
What is irradiation? [1 mark]
Answer:The process of exposing an object to nuclear radiation; the object does not become radioactive.Question 33 · Spec 4.4.2.4 · Safety
State two precautions to reduce exposure to radiation. [2 marks]
Answer:Any two from: handle sources with tongs (1); keep sources in lead-lined boxes (1); limit exposure time (1); wear dosimeter badges (1).Question 34 · Spec 4.4.3.1 · Background radiation
State two natural sources of background radiation. [2 marks]
Answer:Any two from: rocks such as granite (1); radon gas (1); cosmic rays from space (1).Question 35 · Spec 4.4.3.1 · Background radiation
State two man-made sources of background radiation. [2 marks]
Answer:Fallout from nuclear weapons testing (1); nuclear accidents such as Chernobyl (1).Question 36 · Spec 4.4.3.1 · Dose
What unit is radiation dose measured in? [1 mark]
Answer:Sieverts (Sv), often millisieverts (mSv).Question 37 · Spec 4.4.3.2 · Half-lives
Why are isotopes with a long half-life dangerous? [1 mark]
Answer:They stay radioactive for a very long time.Question 38 · Spec 4.4.3.3 · Medical uses
Why is a gamma emitter with a short half-life used as a medical tracer? [2 marks]
Answer:Gamma can pass out of the body to be detected (1); a short half-life means the patient is exposed for less time (1).Question 39 · Spec 4.4.3.3 · Medical uses
How is radiation used to treat cancer? [1 mark]
Answer:Gamma rays or implanted sources are directed at the tumour to kill cancer cells.Question 40 · Spec 4.4.4.1 · Fission
Describe nuclear fission. [3 marks]
Answer:A large unstable nucleus, such as uranium-235, absorbs a neutron (1); it splits into two smaller nuclei, releasing two or three neutrons and gamma rays (1); energy is released as kinetic energy of the products (1).Question 41 · Spec 4.4.4.1 · Chain reaction
What is a chain reaction? [2 marks]
Answer:The neutrons released by fission go on to cause further fission (1); in a reactor it is controlled, but in a bomb it is uncontrolled and causes an explosion (1).Question 42 · Spec 4.4.4.1 · Reactors
How is the chain reaction controlled in a nuclear reactor? [1 mark]
Answer:Control rods absorb neutrons.Question 43 · Spec 4.4.4.2 · Fusion
Describe nuclear fusion. [2 marks]
Answer:Two light nuclei join to form a heavier nucleus (1); some of the mass is converted into energy, which is released (1).Question 44 · Spec 4.4.4.2 · Fusion
Where does nuclear fusion happen naturally? [1 mark]
Answer:In the cores of stars.Question 45 · Spec 4.4.2.1 · Detection
Name a device used to detect radiation. [1 mark]
Answer:A Geiger-Muller tube.Question 46 · Spec 4.4.3.3 · Uses
Why is alpha radiation used in smoke detectors? [1 mark]
Answer:It ionises the air so a current flows; smoke absorbs the alpha particles and the current drops, setting off the alarm.Question 47 · Spec 4.4.1.2 · Isotopes
How many protons, neutrons and electrons are in sodium-23 (atomic number 11)? [2 marks]
Answer:11 protons and 11 electrons (1); 12 neutrons (1).Question 48 · Spec 4.4.1.3 · Atomic model
Why was the plum pudding model replaced? [1 mark]
Answer:It could not explain why some alpha particles were deflected through large angles.Question 49 · Spec 4.4.3.2 · Half-lives
Why should isotopes used inside the body have a short half-life? [1 mark]
Answer:So they do not stay radioactive in the body for long, reducing harm.Question 50 · Spec 4.4.2.4 · Contamination
Why is contamination more dangerous than irradiation? [1 mark]
Answer:The radioactive material stays on or in the body, so exposure continues.