Atomic number and mass number
3 marks · NormalExplain the difference between the atomic number and the mass number of an atom. Give an example of each.
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Must show: Definition of atomic number, Definition of mass number, Example for each
Also accept: Atomic number is number of protons; mass number is total protons and neutrons; example: carbon has atomic number 6 and mass number 12.
Common mistakes: Mixing up definitions; Not giving examples
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Marking points
B1 · 1 mark · Describes atomic number as the number of protons in the atom's nucleus.
B2 · 1 mark · Describes mass number as the total number of protons and neutrons in the nucleus.
B3 · 1 mark · Provides an example of both (e.g., atomic number of hydrogen is 1; mass number of carbon is 12).
Worked solution
Atomic number is the number of protons in an atom's nucleus; mass number is the total number of protons and neutrons.
Example: Helium has atomic number 2 (2 protons), and mass number 4 (2 protons + 2 neutrons).