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GCSE Chemistry · key term
An atom of an element that has the same number of protons as its other atoms but a different number of neutrons.
Used by AQA, Edexcel and OCR
Specification 4.1.1.5, 4.1.2.2 · Paper 1
One of two or more atoms of the same element that have the same number of protons but different numbers of neutrons.
Revise: Atomic Size and MassAtoms of one element with different numbers of neutrons are its isotopes.
Specification 1.9, 1.12, 1.15 · Paper 1, Paper 2
An atom of an element that has the same number of protons as other atoms of that element but a different number of neutrons in its nucleus.
Revise: IsotopesThe word isotope describes a version of an element, not a different element or a different subatomic particle.
An atom of an element that has the same number of protons as other atoms of that element but a different number of neutrons.
Specification C1.2e · Paper 1 (Foundation), Paper 3 (Higher)
One of two or more atoms of the same element that have the same number of protons but different numbers of neutrons.
Revise: Subatomic CalculationsA mass number belongs to one particular isotope and is a whole number. It should not be confused with the relative atomic mass commonly displayed on a periodic table, which can be a decimal because it takes account of the element's isotopes.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
A form of the same element whose atoms contain the same number of protons but different numbers of neutrons.
Revise: Evidence for climate changeSecond, carbon occurs as different isotopes. Fossil fuels contain ancient carbon with an isotopic pattern different from carbon in recently living systems. Measurements of the modern atmosphere show the expected fingerprint of added old, fossil carbon.
An atom of an element with a particular number of neutrons. Isotopes of the same element have the same number of protons but different numbers of neutrons.
When comparing isotopes, state both parts: they have the same number of protons but different numbers of neutrons.
For a question asking how the periodic table developed, give the stages in chronological order: ordering by atomic weight, problems with early tables, Mendeleev’s gaps and changes, successful predictions, then the explanation provided by isotopes and atomic number.
Do not confuse mass number with relative atomic mass. Mass number belongs to one isotope and is a whole number; relative atomic mass is a weighted mean for all the naturally occurring isotopes of an element.
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