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5.1.2Nuclear Physics

THE Nucleus — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 10 parts Lesson 4 of 17 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

5.1.2 The Nucleus — IGCSE PHYSICS notes: Describe the composition of the nucleus, use proton number, nucleon number and nuclide notation, and explain isotopes, fission and fusion.Contents — protons (positive) and neutrons (neutral), together called nucleons.Charge — the nucleus h…

  • Charge and mass (Extended)
  • Proton number (atomic number) Z
  • Nucleon number (mass number) A
  • Number of neutrons
  • Same Z, different A
  • Occurrence

Part 1 of 8Composition of the nucleus

1Contents
  • Contents protons (positive) and neutrons (neutral), together called nucleons.
2Charge
  • Charge the nucleus has an overall positive charge.
3Terms
  • Terms an atom is the nucleus and the electrons, while the nucleus is only the protons and neutrons.
4Charge and mass (Extended)
  • Charge and mass (Extended) the charge is proportional to Z (charge = +Ze) and the mass is approximately proportional to A.

Part 2 of 8Proton number and nucleon number

1Proton number (atomic number) Z
Proton number (atomic number) Z the number of protons in the nucleus, which identifies the element.
  • Hydrogen has Z = 1, sodium has Z = 11 and uranium has Z = 92.
  • Z also equals the number of electrons in a neutral atom.
2Nucleon number (mass number) A
Nucleon number (mass number) A the total number of protons and neutrons.
3Number of neutrons
  • A − Z.
4Nuclide notation
  • AZX, with A at the top and Z at the bottom, such as 146C with 6 protons and 8 neutrons.

Part 3 of 8Isotopes

Isotopes
Isotopes atoms of the same element with the same number of protons but a different number of neutrons.
Same Z, different A
  • Same Z, different A isotopes of an element have the same chemical properties.
Stability
  • Stability some isotopes are unstable (radioactive), such as carbon-14, while others are stable, such as carbon-12.
Occurrence
  • Occurrence isotopes occur naturally, but some are rarer, as only about two in every 10 000 hydrogen atoms are deuterium.

Part 4 of 8Nuclear fission (Extended)

1Process
  • Process a large unstable nucleus such as uranium-235 absorbs a neutron and splits into two smaller daughter nuclei plus two or three neutrons.
2Energy
  • Energy a large amount is released, mostly as kinetic energy of the products.
3Chain reaction
  • Chain reaction the released neutrons can cause further fissions, as used in nuclear power stations.

Part 5 of 8Nuclear fusion (Extended)

1Process
  • Process two light nuclei, such as isotopes of hydrogen, join to form a heavier nucleus.
2Conditions
  • Conditions it needs very high temperature and pressure.
3Source
  • Source it is the energy source of stars.
4Mass
  • Mass in both fission and fusion the products have slightly less mass than the reactants, and this mass is converted into energy.

Part 6 of 8Balancing a nuclear equation (Extended)

1
Write nuclide notation (A on top, Z below) for every particle, including neutrons (10n).
2
Add up the nucleon numbers on the left side.
3
Make the nucleon numbers on the right add to the same total to find any missing A.
4
Repeat for the proton numbers to find any missing Z.
5
Use Z to identify the element and check both totals balance.

Part 7 of 8Fission compared with fusion

FeatureFissionFusion
ProcessHeavy nucleus splitsLight nuclei join
NeedsNeutron absorptionVery high temperature and pressure
FuelU-235, Pu-239Hydrogen isotopes
WhereNuclear reactorsStars
ControlControl rods absorb neutronsHard to achieve on Earth

Part 8 of 8More from the specification

More from the specification
Nuclear density and mass determination
  • Nuclear density and mass determination measuring electron scattering angles against target nuclei provides an empirical means to determine nuclear radius.
Nuclear model
  • Nuclear model a tiny dense positive nucleus holds protons and neutrons, with electrons orbiting around it
Relative charge
  • Relative charge proton +1, neutron 0 and electron -1, with relative masses of about 1, 1 and 1/1836
Alpha particles
  • Geiger and Marsden fired them at thin gold foil;
    • most passed through, some were deflected and a few rebounded, showing a small charged nucleus
Determining structure
  • Determining structure the atomic number gives protons and the mass number minus atomic number gives neutrons, for example chromium has 24 protons
Nuclear model
  • Nuclear model a tiny dense positive nucleus holds protons and neutrons, with electrons orbiting around it
Relative charge
  • Relative charge proton +1, neutron 0 and electron -1, with relative masses of about 1, 1 and 1/1836
Alpha particles
  • Geiger and Marsden fired them at thin gold foil;
    • most passed through, some were deflected and a few rebounded, showing a small charged nucleus
Determining structure
  • Determining structure the atomic number gives protons and the mass number minus atomic number gives neutrons, for example chromium has 24 protons
Nuclear model
  • Nuclear model a tiny dense positive nucleus holds protons and neutrons, with electrons orbiting around it
Relative charge
  • Relative charge proton +1, neutron 0 and electron -1, with relative masses of about 1, 1 and 1/1836
Alpha particles
  • Geiger and Marsden fired them at thin gold foil;
    • most passed through, some were deflected and a few rebounded, showing a small charged nucleus
Determining structure
  • Determining structure the atomic number gives protons and the mass number minus atomic number gives neutrons, for example chromium has 24 protons
Nuclide equation
  • An equation showing nuclei and particles in a nuclear reaction.
Nuclear model
  • Model of the atom with a small dense nucleus surrounded by electrons.
Relative charge
  • Charge compared with the fundamental charge 1.6 × 10−19 C.
Alpha particle
  • Helium nucleus, charge +2.
Alpha scattering
  • Experiment firing alpha particles at gold foil that showed the nuclear atom.

Key terms

TermMeaning
NucleonA proton or a neutron.
Proton number (Z)Number of protons in the nucleus.
Nucleon number (A)Number of protons plus neutrons.
IsotopeAtom of the same element with a different number of neutrons.
Nuclide notationAZX.

Avoid these mistakes

1
Saying isotopes have different proton numbers — they differ in neutron number.
2
Counting electrons in the nucleon number.
3
Mixing up proton number and nucleon number in the notation — A is on top and Z at the bottom.
4
Thinking fission and fusion conserve mass exactly — the products have slightly less mass.

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