| English | Isotope |
|---|---|
| Bahasa Melayu | Isotop |
| 中文 | 同位素 |
Definition
Atoms of the same element that have the same number of protons but different numbers of neutrons.
In exam terms
Isotopes are atoms of the same element that have the same number of protons (same proton number Z) but different numbers of neutrons (different nucleon number A). Because they have the same Z, they have the same chemical behaviour, but their masses differ.
There is no SI unit; isotopes are labelled by their nucleon number.
A correct sentence: "Carbon-12 and carbon-14 are isotopes because both have 6 protons but 6 and 8 neutrons respectively." Some isotopes are stable while others, such as carbon-14, are unstable and radioactive.
Do not confuse it with…
Do not confuse isotopes with different elements. Changing the number of neutrons gives an isotope of the same element; changing the number of protons gives a completely different element.
Also distinguish isotopes from ions: ions differ in the number of electrons, not neutrons.
In Paper 2 you may be asked to define isotope, state what is the same and what is different between two isotopes, or identify a pair of isotopes from their proton and nucleon numbers.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)