1. The sub-atomic particles of an atom consist of protons, electrons and neutrons.
2. The nucleus of an atom consists of only protons and neutrons.
3. The electrons are found in shells outside the nucleus.
4. Only protons and neutrons have mass and it contributes to the mass of an atom.
5. Proton has a relative charge of +1 and a relative mass of 1.
6. Electron has a relative charge of -1 and a relative mass of 1/1840 .
7. Neutron has a relative charge of 0 and a relative mass of 1.
8. An element has a fixed proton number but the same element can have different number of neutrons.
9. Isotopes are atoms of the same element with the same number of protons and electrons but different number of neutrons.
10. Please refer to attached pdf.
11. When an atom has an unequal number of protons and electrons, it is called an ion. Unlike an atom, an ion has an electrical charge.
12. When the ion has more electrons than protons, it has a negative charge.
13. When the ion has more protons than electrons, it has a positive charge.
14. Please refer to attached pdf.
15. For an atom, the number of electrons is equal to the number of protons.
16. Please refer to attached pdf.
17. When an atom forms an ion, the number of electrons changes but the number of protons and neutrons always remains unchanged.
18. An atom forms a positive ion, if it loses electrons and it forms a negative ion, if it gains electrons.
19. Please refer to attached pdf.
20. To get an electronic configuration of an atom, the first electron shell can contain up to 2 electrons and the second and third shells can contain up to 8 electrons.
21. Please refer to attached pdf.
This summary is applicable for GCE ‘O’ Level (Syllabus 5076/5078)
Notes about quick summary:
1. Students must remember all the points in the quick summary, however memorizing is not required as the style of questioning is more application rather than plain recall of facts.
2. Students can refer to the link on how to use the quick summary to aid in your revision.
