Count protons, neutrons and electrons
The idea
Atomic number counts protons; mass number is protons plus neutrons.
Step by step
- Atomic number counts protons; mass number is protons plus neutrons.
- A neutral atom has the same number of electrons as protons.
- A positive ion has lost electrons; a negative ion has gained electrons.
Example
An atom has atomic number 8. How many protons does it have?
Answer
8
Atomic number equals proton count, so there are 8 protons.
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Invent an atom with 8 protons and mass number 18. Calculate its neutrons and its electrons when neutral and when 2−.
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