Curriculum
Science — First Preparatory
Unit 1: Matter
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Unit 2: Forces
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Unit 3: Life
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Unit 4: Earth and Space
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Text lesson
Structure of the Atom
Structure of the Atom
Atomic number and mass number
Atomic number and mass number
- The atomic number is the number of protons in the nucleus.
- It identifies each element.
- The mass number is the total number of protons and neutrons in the nucleus.
- Number of protons = atomic number.
- Number of neutrons = mass number − atomic number.
- In a neutral atom number of electrons = atomic number.
- Example a carbon atom 12C has atomic number 6 and mass number 12. So it has 6 protons, 12 − 6 = 6 neutrons, and 6 electrons.
Structure of the Atom · 2 / 6