Atomic Structure and Valence Electrons

Learning Intentions and Success Criteria

  • Core Learning Intentions:

    • Define a valence electron as an electron that exists in the outermost shell of an atom and takes part in chemical reactions.

    • Identify valence electrons in the first 2020 elements of the Periodic Table.

  • Success Criteria:

    • Define a valence electron with precision regarding its location and role.

    • Identify the exact number and configuration of valence electrons across the first 2020 elements of the Periodic Table.

Fundamental Atomic Structure and Subatomic Particles

Diagram illustrating the basic parts of an atom including the nucleus, protons, neutrons, and electrons

  • Atomic Nucleus:

    • The dense central core of an atom.

    • Composed of two types of nucleons: protons and neutrons bound together.

  • Protons:

    • Located inside the central nucleus.

    • Carry a positive electrical charge (++).

  • Neutrons:

    • Located inside the central nucleus alongside protons.

    • Carry no electrical charge; electrically neutral.

  • Electrons:

    • Positioned outside the nucleus, orbiting around it in specific pathways or shells.

    • Carry a negative electrical charge (−-).

Electron Shells and Valence Electrons

  • Electron Shells (Orbitals):

    • Every atom has a specific, set number of electrons.

    • Electrons orbit the central nucleus in concentric energy "shells" (orbitals).

  • Definition of Valence Electrons:

    • Valence electrons are the electrons that are furthest away from the nucleus.

    • They reside exclusively in the outermost shell of an atom.

    • These specific electrons are responsible for taking part in chemical reactions and forming chemical bonds.

  • Valence Shell:

    • The outermost orbital or energy shell of an atom that houses the valence electrons.

Case Study: Boron Atom Structure

Diagram of a boron atom illustrating valence electrons, the valence shell, and the nucleus

  • Nuclear Composition of Boron:

    • Protons: 55 positively charged particles (++).

    • Neutrons: 66 neutral particles.

    • Nucleus Total: 5 protons+6 neutrons5\text{ protons} + 6\text{ neutrons}.

  • Electron Arrangement in Boron:

    • Total Electrons: 55 negatively charged electrons (−-) balancing the 55 protons in a neutral atom.

    • Inner Energy Shell: Contains 22 inner core electrons orbiting closest to the nucleus.

    • Valence Shell (Outermost Shell): Contains 33 valence electrons orbiting at the greatest distance from the nucleus.

  • Chemical Function:

    • The 33 electrons located in the outermost valence shell are the electrons that directly interact during chemical bonding and reactions.

Practical Activity: Modelling Atomic Structure

  • Task Overview:

    • Model atomic structures using Bohr diagrams.

  • Activity Instructions:

    • Use a structured scaffold or draw custom diagrams to create the Bohr diagram for each of the first 2020 elements of the Periodic Table.

    • For each element, map the central nucleus (protons and neutrons), inner shell electron populations, and identify the outermost valence electrons.