ionisation energy Flashcards
define ionisation energy
the energy required to remove an electron of each atom of one mole of a gaseous element to form one mole of gaseous +1 ions
what are the factors affecting the size of ionisation energy?
- number of shells so electron shielding
- nuclear charge
- atomic radius
- whether the electron is on its own in an orbital or is paired
how does electron shielding affect ionisation energy?
- the more electron shielding there is, the less the ionisation energy
- repulsion effect reduces the nuclear attraction on the valence electrons making them easier to be removed
how does nuclear charge affect ionisation energy?
- as the nuclear charge increases, the ionisation energy increases
- nuclear attraction on valence electrons are stronger
- harder to remove valence electron and more energy required
how does atomic radius affect the ionisation energy?
- as the atomic radius increases, the ionisation energy decreases
- nuclear attraction on valence electrons decrease
how does the electrons being paired or unpaired in an orbital affect the ionisation energy?
- paired electrons in an orbital will face some repulsion making it easier for them to be removed
what is the general trend in ionisation energy across period two and three?
- throughout the whole of period two, the valence electrons are in the second level orbital
- these are all the same sort of differences from the nucleus as they are all screened by the 1s^2 electrons
- the major difference is the increasing number of protons
- nuclear charge on valence electrons increase
- they need more energy to be removed
- same trend for period three except the valence electrons are screened by the 1s^2 , 2s^2 and 2p^6 electrons
what is the difference between the general trends in period two and three?
- ionisation energy of period three elements are lower
- elements in period three have more electron shielding
- less nuclear attraction on valence electrons
why is there are an exception between group 2 and group 3 elements so for example between beryllium and boron?
- we would expect boron to have a higher first ionisation energy because it has more protons
- but its valence electron is in a p orbital which is further away from nucleus
- it also has more electron shielding considering the 2s^2 electrons
- smaller nuclear attraction on valence electrons
why is there a drop between groups 5 and 6?
- the screening is identical
- the electron is being removed from an identical orbital
- the electrons in the orbital are paired and face repulsion from each other
- electron is easier to be removed
why doesn’t the ionisation energy decrease for the rest across the period too like from N to O regarding the pairings of the electrons in the orbitals?
- it isn’t a new factor anymore
- the increase in protons outweighs this factor and causes the ionisation energies to increase
what is the trend in ionisation energies down the group?
- decreases
- number of shells increase so electron shielding increases
- nuclear attraction on outer electrons decrease
- less energy required to remove the outer electron
why do we not take into account the nuclear charge increasing when looking at trend down the group?
- although the nuclear charge increases, the electron shielding also increases so the net charge the valence electron would be roughly the same
what is the trend in ionisation energy for transition metals?
- apart from zinc at the end, the ionisation energies are all much the same
how does ionisation energy relate to reactivity?
- the fall in ionisation energies results in lower activation energies and faster reactions
