Isotopes

    OCR
    GCSE

    Isotopes are defined as atoms of the same element possessing identical proton numbers but differing neutron numbers, resulting in variations in nucleon number. While isotopes exhibit identical chemical properties due to unchanged electron configurations, their physical properties—specifically nuclear stability and mass—vary significantly. Candidates must demonstrate proficiency in interpreting standard nuclear notation to determine subatomic particle composition. Furthermore, the concept underpins the calculation of relative atomic mass and provides the mechanism for radioactive decay in unstable nuclei.

    0
    Objectives
    3
    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating isotopes have the same number of protons (or same atomic number)
    • Award 1 mark for stating isotopes have a different number of neutrons (or different mass number)
    • Credit responses that calculate neutron number correctly by subtracting atomic number from mass number
    • Award 1 mark for recognizing that neutral isotopes of the same element contain the same number of electrons

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the mass difference, but you must specify that the proton number remains the same to get the mark"
    • "Be careful with your terminology: use 'nucleon number' or 'mass number', not just 'top number'"
    • "Good calculation of the neutron count; now explain why this difference doesn't affect the chemical reactions of the atom"
    • "You have confused isotopes with ions—remember isotopes differ in neutrons (mass), while ions differ in electrons (charge)"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating isotopes have the same number of protons (or same atomic number)
    • Award 1 mark for stating isotopes have a different number of neutrons (or different mass number)
    • Credit responses that calculate neutron number correctly by subtracting atomic number from mass number
    • Award 1 mark for recognizing that neutral isotopes of the same element contain the same number of electrons

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When defining isotopes, explicitly mention 'same number of protons' and 'different number of neutrons'—this phrasing is safer than using 'atomic/mass number'
    • 💡Check the key on the provided Periodic Table carefully; OCR sometimes flips the position of Mass Number and Atomic Number compared to other boards
    • 💡Remember that isotopes of the same element have identical chemical properties because their electron configuration is unchanged

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Defining isotopes as 'atoms with different masses' without specifying they are atoms of the same element/same proton number
    • Stating that isotopes have different numbers of electrons, confusing them with ions
    • Using the relative atomic mass from the Periodic Table instead of the specific mass number given in the question for neutron calculations

    Study Guide Available

    Comprehensive revision notes & examples

    Read Study Guide

    Key Terminology

    Essential terms to know

    Definition in terms of subatomic particles (protons and neutrons)
    Standard nuclear notation and nucleon number calculation
    Distinction between physical properties (mass) and chemical properties (reactivity)
    Calculation of relative atomic mass from isotopic abundance

    Likely Command Words

    How questions on this topic are typically asked

    Define
    Calculate
    Explain
    Describe
    Compare

    Ready to test yourself?

    Practice questions tailored to this topic