(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.