1st Ionisation Energies

1st Ionisation Energies

1. Groups

   • Elements placed in groups as they show many similar physical + chemical properties. Elements in groups occupy similar positions on plot of 1st IE against atomic no.
   • 1st IE generally decrease down vertical group, with increasing atomic no. With increasing proton no, in any group:
     • Positive nuclear charge increases
     • Atomic radius increases so distance of outer electrons from nucleus also increase with each new shell
     • Shielding effect of filled inner electron shells increases as no. of inner shells grows.
   • Combined distance + shielding effects overcome effect of increasing nuclear charges from element to element down any group. Therefore 1st IE decrease down group.

2. Reactivity of elements

   • IE give measure of energy required to remove electrons from atoms + pos ions. Lower 1st IE of element, more easily element forms pos ions during reactions:
     • Main reason for metallic nature of elements on 'left' of Periodic Table + increasingly metallic nature of elements down all groups.
   • In elements with low 1st IE, 1 or more electrons relatively free to move from atom to atom in metallic bonding of structure.
   • Characteristic chemical properties of metallic elements include formation of metals with O, Cl or H2O e.g. formation of pos ions is 1 of several stages involving enthalpy changes.Elements with low 1st ionisation energies usually don't react more quickly/vigorously.
     • In any period, Group 1 elements have lowest 1st IE + are most reactive metals. Also have lower 1st IE going down group, with increasing atomic no. + become more reactive.

3. Successive IE

   • Pattern of successive IE for element used to:
     • Provide evidence for general pattern of electron shells
     • Predict simple electronic configuration of an element
     • Confirm position of element in Periodic Table
   • For any 1 element, successive IE steadily increase as electrons are removed. Large increase occurs between 2 successive IE when next electron is removed from lower electron shell.