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    Understandings 

    ● Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons).
    Guidance
    Relative masses and charges of the sub-atomic particles should be known, actual values are given in
    section 4 of the IB data booklet. The mass of the electron can be considered negligible.
    ● Negatively charged electrons occupy the space outside the nucleus.
    ● The mass spectrometer is used to determine the relative atomic mass of an element from its
    isotopic composition.
    Guidance
    The operation of the mass spectrometer is not required.

    Applications and skills 

    ● Use of the nuclear symbol notation AZ X to deduce the number of protons, neutrons, and
    electrons in atoms and ions.
    ● Calculations involving non-integer relative atomic masses and abundance of isotopes from given data, including mass spectra.
    Guidance
    Specific examples of isotopes need not be learned.

    Inquiry question

    How are electrons arranged in an atom?

    History of atomic theory 

    The video "The History of Atomic Chemistry" discusses the different theories throughout history about the structure of an atom. The following theories are mentioned in the video: 
    • Thomson's "plum pudding" model 
    • Rutherford's gold foil experiment
    • Bohr model 
    • Heisenberg's theory  - Quantum model 
    Picture
    Notes
    Watch the video and take notes about the  4 Models or experiments listed above

    Test yourself 

    Exam questions 
    ​
    1. Which statement about the numbers of protons, electrons and neutrons in an atom is always correct?
    A.    The number of neutrons minus the number of electrons is zero.
    B.    The number of protons plus the number of neutrons equals the number of electrons.
    C.    The number of protons equals the number of electrons.
    D.    The number of neutrons equals the number of protons.
    (Total 1 mark)

    ​2. Iron has three main naturally occurring isotopes which can be investigated using a mass spectrometer.
        The first stage in the operation of the mass spectrometer is vaporization. The iron is then ionized.
    (i)    Explain why the iron is ionized.
    ......................................................................................................................................
    ......................................................................................................................................
    ......................................................................................................................................
    ......................................................................................................................................
    (2)
    (ii)    Explain why a very low pressure is maintained inside the mass spectrometer.
    ......................................................................................................................................
    ......................................................................................................................................
    (1)
    (Total 3 marks)

    History of atomic theory and structure of atom 

    Looking at the history of the atom structure from an Art focus. This video is taken from the EdX course Science in Art. See the link below to access the full course.