- Nuclear Symbol (show what the top and bottom number represent) = Top number: Mass Number (A), Bottom number: Atomic Number (Z)
- Atomic Number = Number of protons (also equals number of electrons in a neutral atom)
- Mass Number = Protons + Neutrons
- Protons = Atomic Number
- Neutrons = Mass Number - Atomic Number
- Electrons = Number of protons (in a neutral atom)
In the table above, the mass number for lithium is 8. An alternate symbol for this isotope of lithium is Li-8. How do you know the atomic number for this isotope?
→ The atomic number is determined by the element’s identity (lithium), which is always 3, regardless of the isotope.
Now it’s your turn!
Element: Carbon
Nuclear Symbol: ¹²C
Atomic #: 6
Mass #: 12
Protons (p⁺): 6
Neutrons (n⁰): 6
Electrons (e⁻): 6
Element: Oxygen
Nuclear Symbol: ¹⁷O
Atomic #: 8
Mass #: 17
Protons (p⁺): 8
Neutrons (n⁰): 9
Electrons (e⁻): 8
Element: Phosphorus
Nuclear Symbol: ³¹P
Atomic #: 15
Mass #: 31
Protons (p⁺): 15
Neutrons (n⁰): 16
Electrons (e⁻): 15
Element: Argon
Nuclear Symbol: ⁴⁰Ar
Atomic #: 18
Mass #: 40
Protons (p⁺): 18
Neutrons (n⁰): 22
Electrons (e⁻): 18
Parent Tip: Review the logic above to help your child master the concept of subatomic particle worksheet.
