What is the Periodic Table?
An arrangement of elements by increasing atomic number
What is periodicity?
A trend in physical and chemical properties across a period. A property displayed by the Periodic Table.
What do elements in groups share?
Similar chemical properties
Define first ionisation energy
The energy required for removal of one mole of electrons from one mole of gaseous atoms, producing one mole of 1+ ions. In kJmol^-1.
Successive ionisation energies?
Energy required for removal of the second/third/fourth… electron from one mole of an atom’s ions (not ‘n’ electrons)
Trend in first ionisation enthalpies down a group?
- Decreases
- Atomic radius increases; distance between the nucleus and the outer electron increases
- Shielding effect increases (more filled inner shells)
- (Although nuclear charge increases, outweighed by other effects)
- Overall nuclear attraction decreases; less energy is needed to remove the highest energy electron
General trend in first ionisation enthalpies across a period?
- Increases
- No change in shielding effect
- Nuclear charge increases (greater atomic number)
- Atomic radius decreases
- Overall nuclear attraction increases; more energy is needed to remove the highest energy electron
Explain the decrease in first ionisation enthalpy between Be and B
- Be has its highest energy electron in subshell 2s, while B has highest energy electron in subshell 2p
- The subshell 2p has a higher energy than the subshell 2s
- Thus, less energy is needed to remove the electron in 2p than in 2s
Explain the decrease in first ionisation enthalpy between N and O
- N contains unpaired electrons in its orbitals, whereas O contains an electron pair
- Thus, removal of the outer electron in O requires less energy, as this reduces electron pairing
