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5.1.3Nuclear Physics

Protons, Neutrons and Electrons — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 5 of 17 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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5.1.3 Protons, Neutrons and Electrons — IGCSE PHYSICS notes: Compare the charge and mass of the three particles and use proton number and nucleon number to describe atoms, ions and isotopes.ParticleRelative chargeRelative massWhere foundProton+11NucleusNeutron01NucleusElectron−1N…

  • Fundamental charge
  • Nuclear charge
  • Nuclear mass
  • Neutral atom
  • Positive ion
  • Negative ion

Section 1 of 9The three particles

ParticleRelative chargeRelative massWhere found
Proton+11Nucleus
Neutron01Nucleus
Electron−1Negligible (about 1/2000)Orbiting the nucleus
The three particles
Relative charge
  • Relative charge the ratio of a particle's charge to the fundamental charge, so it has no units.
Fundamental charge
  • Fundamental charge the size of the charge on a proton or electron, 1.6 × 10−19 C.

Section 2 of 9Nuclear charge and mass (Extended)

Nuclear charge
  • Nuclear charge the proton number multiplied by +1.
Nuclear mass
  • Nuclear mass the nucleon number multiplied by 1, because the mass of the electrons is negligible.
Mass unit
  • Mass unit a relative mass of 1 equals 1.67 × 10−27 kg.

Section 3 of 9Neutral atoms and ions

Neutral atom
  • Neutral atom it has the same number of electrons as protons, so the charges cancel.
Positive ion
  • Positive ion an atom that loses electrons, such as Na+ with 11 protons and 10 electrons.
Negative ion
  • Negative ion an atom that gains electrons, such as Cl− with 17 protons and 18 electrons.
Nucleus unchanged
  • Nucleus unchanged only electrons change when an ion forms, so the element does not change.

Section 4 of 9Proton number and nucleon number

Proton number Z
Proton number Z the number of protons, which fixes the element and the number of electrons in a neutral atom.
Nucleon number A
Nucleon number A the total number of protons and neutrons, which fixes the mass.
Neutrons
  • N = A − Z.
Electrons
  • Electrons they do not count in A because their mass is negligible.
Nuclide notation
  • Nuclide notation written AZX, with A at the top and Z at the bottom.

Section 5 of 9Isotopes

Isotopes
Isotopes
Isotopes atoms of the same element with the same number of protons but a different number of neutrons.
Different nucleon numbers
  • Different nucleon numbers each element can have more than one isotope.
Chemical behaviour
  • Chemical behaviour it is controlled by the electrons, so isotopes behave identically in chemical reactions.
Stability
  • Stability isotopes can be unstable and more likely to decay, as carbon-14 has two more neutrons than stable carbon-12.
Hydrogen isotopes
  • Hydrogen isotopes hydrogen-1 (one proton), deuterium and tritium (one proton and two neutrons, radioactive).
    • (one proton and one neutron)
  • Chlorine has isotopes 3517Cl and 3717Cl with 18 and 20 neutrons.

Section 6 of 9Charge of an ion

Total charge
  • Total charge the number of protons minus the number of electrons.
Nucleus
  • Nucleus it has a charge of +Z.
Mass estimate
  • Mass estimate each proton and neutron has a mass of about 1 u, so the nucleon number estimates the mass of the atom.

Section 7 of 9More from the specification

More from the specification
Subatomic particle identification
  • Subatomic particle identification analyzing charge-to-mass ratios in deflection chambers provides an experimental means to identify nucleons and orbital electrons.
Fission
  • Splitting of a large nucleus releasing energy.
Fusion
  • Joining of light nuclei into a heavier one.
Nuclear fission
  • The splitting of a large nucleus into two smaller nuclei, releasing energy.
Nuclear fusion
  • Joining of light nuclei to form a heavier nucleus, releasing energy.
Alpha particle
  • Helium nucleus, charge +2.
Alpha scattering
  • Experiment firing alpha particles at gold foil that showed the nuclear atom.
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.
Atomic number
  • Atomic number another name for the proton number Z; the periodic table is arranged in order of this number.
Mass number
  • Mass number another name for the nucleon number A, the total of protons and neutrons in the nucleus.
Net charge
  • Net charge the overall charge of a particle, found by comparing protons and electrons;
    • equal numbers give zero.

Section 8 of 9Key terms

TermMeaning
Proton number (Z)Number of protons in the nucleus.
Nucleon number (A)Total number of protons and neutrons.
IsotopeAtom of the same element with a different number of neutrons.
Relative chargeCharge compared with the fundamental charge 1.6 × 10−19 C.
IonCharged atom formed by gaining or losing electrons.

Section 9 of 9Exam technique

1
Saying isotopes have different numbers of protons — they have the same number of protons.
2
Counting electrons in the nucleon number.
3
Forgetting that neutral atoms have equal numbers of protons and electrons.
4
Thinking an ion has a different number of protons from its atom — only the electrons change.

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