Electron structure ⚛️

• The maximum number of electrons that the first four shells can hold are:

  • Shell 1= 2
  • Shell 2= 8
  • Shell 3= 18
  • Shell 4= 32
• Shells are regarded as energy levels. The energy increases as the shell number increases. The shell number or energy level number is called the principal quantum number n.
• Shells are made up of atomic orbitals
• An atomic orbital is region around the nucleus that can hold up to 2 electrons with opposite spins.
• An atomic orbital can be visualised as a region of space where there is a high probability of finding a electron.
• In an s-orbital, the electron cloud is the shape of a sphere.

  Every shell from n=1 contains one s-orbital

  The greater the shell number, n, the greater the radius of its s-orbital
• In a p-orbital, the electron cloud is the shape of dumb-bell.

  There are three separate p-orbitals at right angles to each other: Px, Py, and Pz

  Each shell form n=2 contains three p-orbitals

  The greater the shell number, the further away form the nucleus the p-orbital is.
• Each shell from n=3 contains five d-orbitals
• Each shell from n=4 contains seven f-orbitals
• Within a shell, orbitals of the same type are grouped together as sub-shells

  e.g. shell 1 contains the sub-shell 1s, shell 2 contains the sub-shells 2s and 2p, shell 3 contains the sub-shells 3s, 3p, and 3d, shell 4 contains the sub-shells 4s, 4p, 4d, and 4f
• Each new shell gains a new type of orbital
• Two electrons fit into one orbital so the number of electrons that fit into each sub-shell are:

  s, 2

  p, 6

  d, 10

  f, 14
• Orbitals fill in order of increasing energy
• The 3d sub-shell is at a higher energy than the 4s sub-shell so 4s fills up before 3d. Therefore the filling order is 3p, 4s, 3d, 4p, 4d
• Two electrons in an orbital always have opposite spins. This counteracts the repulsion between the negatively charged electrons.
• When drawing an electrons-in-box model, an electron is drawn as a half arrow pointing in the direction of it's spin (up or down)
• Orbitals with the same energy are occupied singly first. One electron occupies each orbital before they start pairing.

  This prevents any repulsion between paired electrons until there is no further orbital available at the same energy level
• Shorthand electron configurations are electron configurations expressed more simply in terms of the previous noble gas in the periodic table plus the outer electron sub-shells
• The periodic table can be divided into blocks corresponding to their highest energy sub-shell

  • s block= the highest energy electrons are in the s sub-shell (left block of two groups on periodic table)
  • p block= highest energy electrons are in the p sub-shell (right block of six groups on periodic table)
  • d block= highest energy electrons are in the d sub-shell (centre block of ten groups)
• When forming ions of the s and p block elements, the highest energy sub-shells lose or gain electrons
• For the d block elements, the 4s sub-shell is at a lower energy than the 3d sub-shell so it fills up first. The energies of the 4s and 3d sub-shells are very close together and, once filled, the 3d energy level falls below the 4s energy level. This means that:

  • The 4s sub-shell fills before the 3d sub-shell
  • The 4s sub-shell empties before the 3d sub-shell
• An electron can be thought of as a negative charge cloud with the shape of the orbital, referred to as an electron cloud
• An orbital can hold one or two electrons, no more
• there are different types of orbitals: s-, p-, d-, and f-orbitals
• each type of orbital has a different shape