Electron Structure

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  • Electron Structure
    • Atomic Orbitals
      • S-orbital
        • Spherical shape
        • From energy shell 1 upwards, each level contains one s orbital within an s sub-shell
      • P-orbital
        • Have a 3D dumb bell shape
        • From energy shell 2 upwards, each level contains 3 p orbitals within a p sub-shell
        • Each orbital holds 2 electrons
        • Total of 6 p electrons in a full p sub-shell
      • D-orbitals
        • 5 d-orbitals within a d sub-shell
        • Total of 10 electrons in a full d sub-shell
        • More complex shape than p-orbitals
      • An orbital is a space around the nucleus that can hold up to 2 electrons in opposite spin
    • 3rd and 4th Main Electron Shells Overlap
      • The 4th shell starts to fill before the 3rd level is full
        • Electrons go into 4s before 3d
        • 4s also empties before 3d
    • Periodic Trend in Electron Configuration
      • Across a Period
        • Each period starts with an electron in the new highest energy shell
        • The s and p sub-shell are filled in the same way
      • Down a Group
        • Elements within the same group have the same number of electrons in the outer shell and in each sub-shell
    • Electron Configuration of Ions
      • Positive Ions
        • Electrons are removed from the highest energy level first
      • Negative Ions
        • Electrons will go into the lowest unoccupied energy level
    • Trends in Atomic Radii
      • Factors Affecting atomic radii (size of atom)
        • Strength of attraction between nucleus and electrons
        • Shielding: strength of repulsion between outer shell electrons and the other electrons in the inner shells
      • With Increasing Atomic Number
        • Atomic radius decreases across a Period
          • Same shielding but increasing attraction
        • Atomic radius increases down a group
          • More full inner shells increases shielding so there is decreasing attraction
    • Ionisation Energy
      • First IE is the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
      • Trends in First IE
        • Group Trend
          • Decreases going down any group as the electron is removed from a shell further from the nucleus so is more shielded from the pull of the nucleus
        • Period Trend
          • Increases across any period as there is the same shielding but has an increasing number of protons creating a stronger nuclear attraction
      • Successive Ionisation Energies
        • Each successive IE is larger than the one before because:
          • As an electron is removed, the shell will be drawn closer to the nucleus
          • As distance decreases, nuclear attraction increases

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