2. Atomic structure

2. Atomic structure

2.1 The nuclear atom

Nature of science:

  • Evidence and improvements in instrumentation - alpha particles were used in the development of the nuclear model of the atom that was first proposed by Rutherford.

  • Paradigm shifts - the subatomic particle theory of matter represents a paradigm shift in science that occurred in the late 1800s.

Understandings:

  • Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons).

  • 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.

Applications and skills:

  • Use of the nuclear symbol notation AZX 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.

2.2 Electron configuration

Nature of science:

  • Developments in scientific research follow improvements in apparatus - the use of electricity and magnetism in Thomson’s cathode rays.

  • Theories being superseded—quantum mechanics is among the most current models of the atom.

  • Use theories to explain natural phenomena - line spectra explained by the Bohr model of the atom.

Understandings:

  • Emission spectra are produced when photons are emitted from atoms as excited electrons return to a lower energy level.

  • The line emission spectrum of hydrogen provides evidence for the existence of electrons in discrete energy levels, which converge at higher energies.

  • The main energy level or shell is given an integer number, n, and can hold a maximum number of electrons, 2n².

  • A more detailed model of the atom describes the division of the main energy level into s, p, d and f sub-levels of successively higher energies.

  • Sub-levels contain a fixed number of orbitals, regions of space where there is a high probability of finding an electron.

  • Each orbital has a defined energy state for a given electronic configuration and chemical environment and can hold two electrons of opposite spin.

Applications and skills:

  • Description of the relationship between colour, wavelength, frequency and energy across the electromagnetic spectrum.

  • Distinction between a continuous spectrum and a line spectrum.

  • Description of the emission spectrum of the hydrogen atom, including the relationships between the lines and energy transitions to the first, second and third energy levels.

  • Recognition of the shape of an s atomic orbital and the px, py and pz atomic orbitals.

  • Application of the Aufbau principle, Hund’s rule and the Pauli exclusion principle to write electron configurations for atoms and ions up to Z = 36.

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