The atom
Cambridge IGCSE Physics (0625) · Unit 5: Nuclear physics · 6 flashcards
The atom is topic 5.1.1 in the Cambridge IGCSE Physics (0625) syllabus , positioned in Unit 5 — Nuclear physics , alongside The nucleus, Detection of radioactivity and The three types of nuclear emission. In one line: A positive ion is an atom that has lost one or more electrons, resulting in a net positive charge. The number of protons in the nucleus is now greater than the number of electrons orbiting the nucleus.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).
The deck below contains 6 flashcards — 1 definition — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
The term 'positive ion' in the context of atomic structure
A positive ion is an atom that has lost one or more electrons, resulting in a net positive charge. The number of protons in the nucleus is now greater than the number of electrons orbiting the nucleus.
What the Cambridge 0625 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Describe Describe the structure of an atom in terms of a positively charged nucleus and negatively charged electrons in orbit around the nucleus
- Know Know how atoms may form positive ions by losing electrons or form negative ions by gaining electrons
- Describe Describe how the scattering of alpha (α) particles by a sheet of thin metal supports the nuclear model of the atom, by providing evidence for: (a) a very small nucleus surrounded by mostly empty space (b) a nucleus containing most of the mass of the atom (c) a nucleus that is positively charged Supplement
Describe the structure of an atom, including the location and charge of its constituent particles.
An atom consists of a central, positively charged nucleus. Orbiting the nucleus are negatively charged particles called electrons. The nucleus contains protons which have a positive charge, and neutrons which have no charge.
State the type of charge, if any, carried by each of the following subatomic particles: electron, proton, neutron.
Electron: Negative (-)
Proton: Positive (+)
Neutron: No charge (neutral)
Define the term 'positive ion' in the context of atomic structure.
A positive ion is an atom that has lost one or more electrons, resulting in a net positive charge. The number of protons in the nucleus is now greater than the number of electrons orbiting the nucleus.
State one way an atom can become a negative ion. Include what happens to the number of protons and electrons.
An atom becomes a negative ion by gaining one or more electrons. The number of protons remains the same, but the number of electrons increases, resulting in a net negative charge.
Describe how the scattering of alpha particles in Rutherford's gold foil experiment provides evidence for a very small nucleus surrounded by mostly empty space.
Most alpha particles passed straight through the gold foil, indicating that the atom is mostly empty space. A small number of alpha particles were deflected at large angles, suggesting they encountered a very small, dense, positively charged nucleus. The relatively infrequent large angle deflections imply the nucleus occupies only a tiny fraction of the atom's total volume.
State two observations from the alpha particle scattering experiment that led Rutherford to conclude that the nucleus contains most of the atom's mass.
1. A very small proportion of alpha particles were deflected through large angles (greater than 90°).
2. Some alpha particles were deflected almost directly back towards the source (180°). These observations suggest a concentration of mass capable of causing significant deflection.
Key Questions: The atom
Define the term 'positive ion' in the context of atomic structure.
A positive ion is an atom that has lost one or more electrons, resulting in a net positive charge. The number of protons in the nucleus is now greater than the number of electrons orbiting the nucleus.
More topics in Unit 5 — Nuclear physics
The atom sits alongside these Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this The atom deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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