LA

(40) GCSE Chemistry Revision "Atomic Number and Mass Number"

Understanding Atomic Structure

  • Nucleus and Electrons

    • Atoms consist of a central nucleus and surrounding electrons.

    • Electrons: Negative charge.

    • Nucleus: Contains protons (positive charge) and neutrons (neutral).

    • Atoms have no overall charge due to balance of protons and electrons.

The Periodic Table and Atomic Numbers

  • Periodic Table: Lists elements with specific properties.

  • Each element’s symbol has two key numbers:

    • Atomic Number:

      • Represents the number of protons.

      • Example: Lithium has an atomic number of 3, meaning it has 3 protons and 3 electrons.

    • Mass Number:

      • Total of protons and neutrons in the nucleus.

      • Example: Lithium has a mass number of 7 (3 protons + 4 neutrons).

  • Calculation of Neutrons:

    • Neutrons = Mass Number - Atomic Number.

Examples of Elements

  • Boron:

    • Protons: 4, Neutrons: 5, Electrons: 4.

  • Sodium:

    • Protons: 11, Neutrons: 12, Electrons: 11.

  • Fluorine:

    • Protons: 9, Neutrons: 10, Electrons: 9.

  • Phosphorus:

    • Protons: 15, Neutrons: 16, Electrons: 15.

Isotopes

  • Definition: Isotopes are variants of the same element with different neutron counts.

  • Example: Lithium has isotopes.

    • Most isotopes of lithium: 3 protons, 4 neutrons.

    • Common Isotopes of Carbon:

      • Isotope 1: 6 protons, 6 neutrons.

      • Isotope 2: 6 protons, 7 neutrons.

      • Isotope 3: 6 protons, 8 neutrons.

  • Common isotopes of Chlorine:

    • Isotope 1: 17 protons, 18 neutrons.

    • Isotope 2: 17 protons, 20 neutrons.

Ions

  • Definition: Ions are atoms with an overall charge due to the loss or gain of electrons.

    • Positive ions (cations): Lost electrons.

    • Negative ions (anions): Gained electrons.

  • Examples:

    • Sodium Ion (Na+): 11 protons, 12 neutrons, 10 electrons (lost one electron).

    • Fluoride Ion (F-): 9 protons, 10 neutrons, 10 electrons (gained one electron).

  • Practice:

    • Oxide Ion (O^2-): 8 protons, 8 neutrons, 10 electrons (gained two electrons).

    • Aluminium Ion (Al^3+): 13 protons, 14 neutrons, 10 electrons (lost three electrons).

Conclusion

  • Additional resources available for further practice on atomic structure and ions.