Orbitals

• Subshells contain one or more?atomic orbitals
• Orbitals exist at?specific?energy levels and electrons can only be found at these specific levels,?not?in between them
  • Each atomic orbital can be occupied by a maximum of two electrons

   

• This means that the number of orbitals in each subshell is as follows:
  • s?: one orbital (1 x 2 = total of 2 electrons)
  • p?: three orbitals ( 3 x 2 = total of 6 electrons)
  • d?: five orbitals (5 x 2 = total of 10 electrons)
  • f?: seven orbitals (7 x 2 = total of 14 electrons)

   

• The orbitals have specific 3-D shapes

s orbital shape

• The s orbitals are?spherical?in shape
• The?size?of the s orbitals increases with increasing shell number
  • E.g. the s orbital of the?third?quantum shell (n?= 3) is bigger than the s orbital of the?first?quantum shell (n?= 1)

   

p orbital shape

• The p orbitals have a?dumbbell shape
• Every shell has three p orbitals except for the first one (n?= 1)
• The p orbitals occupy the x, y and z axes and point at right angles to each other, so are oriented?perpendicular?to one another
• The lobes of the p orbitals become?larger?and?longer?with increasing shell number

Representation of orbitals (the dot represents the nucleus of the atom) showing spherical s orbitals (a), p orbitals containing ‘lobes’ along the x, y and z axis

• Note that the shape of the d orbitals is?not?required

An overview of the shells, subshells and orbitals in an atom

• Electrons can be imagined as small?spinning charges?which rotate around their own axis in either a?clockwise?or?anticlockwise direction
  • The spin of the electron is represented by its direction
  • The spin creates a tiny magnetic field with N-S pole pointing up or down

   

Electrons can spin either in a clockwise or anticlockwise direction around their own axis

• Electrons with the same?spin?repel each other which is also called?spin-pair repulsion
  • Therefore, electrons will occupy separate orbitals in the same subshell first to minimise this repulsion and have their?spin?in the same direction
  • They will then pair up, with a second electron being added to the first p orbital, with its spin in the?opposite?direction

   

• This is known as?Hund's Rule
  • E.g. if there are three electrons in a?p subshell, one electron will go into each px, py?and pz?orbital

   

Electron configuration: three electrons in a p subshell

• The principal quantum number indicates the energy level of a particular shell but also indicates the energy of the electrons in that shell
  • A 2p electron is in the second shell and therefore has an energy corresponding to?n?= 2

   

• Even though there is repulsion between negatively charged electrons, they occupy the same region of space in orbitals
• An orbital can only hold two electrons and they must have opposite spin - the is known as the?Pauli Exclusion Principle
• This is because the energy required to jump to a higher?empty orbital is?greater?than the inter-electron repulsion
• For this reason, they pair up and occupy the lower energy levels first