AQA A-Level Chemistry 7405
Atomic Structure
Amount of Substance
Bonding
Energetics and Thermodynamics
Kinetics
Chemical Equilibria
Redox and Electrochemistry
Acids and Bases
Periodicity and Group Chemistry
Period 3 Elements and Their Oxides
Transition Metals
Introduction to Organic Chemistry
Hydrocarbons
Halogenoalkanes, Alcohols and Organic Analysis
Carbonyls, Carboxylic Acids and Derivatives
Aromatic Chemistry and Amines
Polymers, Amino Acids, Proteins and DNA
Organic Synthesis, NMR and Chromatography
Atomic Structure
Mass Number and Isotopes
- 3 things to know
- Papers 1 and 3
Overview
Mass number, atomic number, and how isotopes of the same element differ.
What you need to know
Answer each one before you reveal it.
What is the mass number (A) of an atom?
What is the atomic number (Z) of an atom?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the mass number (A) of an atom?
Model answer
The total number of protons and neutrons in the nucleus of an atom.
- 2
What is the atomic number (Z) of an atom?
Model answer
The number of protons in the nucleus of an atom.
- 3
How do you determine the number of protons in an atom using atomic number?
Model answer
The number of protons equals the atomic number.
- 4
How do you determine the number of neutrons in an atom?
Model answer
Number of neutrons = mass number − atomic number (A − Z).
- 5
How do you determine the number of electrons in a neutral atom?
Model answer
The number of electrons equals the atomic number (same as the number of protons).
- 6
How do you determine the number of electrons in an ion?
Model answer
Number of electrons = atomic number − charge (subtract the charge for positive ions, add for negative ions).
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