Ionisation energy Flashcards
Define first ionisation energy
The first ionisation energy of an element is the energy required to remove 1 electron from each atom in a mole of gaseous atoms, to produce 1 mole of electrons and 1 mole of gaseous ions each with a single positive charge
What are the units of ionisation energy?
kJmol-1
Give the equation for first ionisation energy
X(g) ———-> X+(g) + e-
What are the three factors that affect ionisation energy?
- Distance from the nucleus
- Nuclear charge
- Shielding
How does distance from the nucleus affect IE and why?
- as the distance from the nucleus (i.e. atomic radius) increases, IE decreases
- this is because as the distance increases the attraction between the + nucleus and e- decreases
- so it is easier to remove an electron
How does sheilding affect IE and why?
- shielding is repulsion caused by e- in the inner shells between the nucleus and the outer electron
- the more inner shell electrons, the greater the repulsion
- the greater the repulsion the easier it is to remove the outermost electron
- and so ionisation energy decreases
How does nuclear charge affect IE and why?
- when the nuclear charge gets more positive (i.e. more protons in the nucleus) IE increases
- this is because the attraction between the + nucleus and e- becomes stronger
- and so it is more difficult to remove an electron
What would happen if you did continuous successive ionisation energies from an atom?
You would carry on removing one electron until nothing remained but a bare nucleus
Successive Ionisation energy graphs of a particular element give evidence for what?
Electron arrangement, in s, p, d, f orbitals
If you carried out successive ionisation energies, what would happen as you remove an extra electron each time?
- the IE would increase because you would be removing them from a +1 ion, then a 2+ ion ect
- there would be a big jump in IE as you plucked an electron from a new subshell
- electrons in the outermost shells (the first electrons) would be the easiest to remove because they are furthest from the + nucleus
What is the trend for IE down a group and why does this happen despite what?
- down a group IE decreases
This is because…
i) the atoms are getting bigger; atomic radius increasing; distance between + nucleus and e- increasing; less attraction
ii) more shielding caused by inner shell electrons; more repulsion
DESPITE the nuclear charge increasing
What is the general trend for IE across a period, and why does this happen?
- across a period IE generally increases
This is because…
i) there is increased nuclear charge; more protons
ii) atomic radius is decreasing; less distance between nucleus and e-; stronger attraction
Where do you find the ‘dips’ in the trend of IE across a period, and why…
a) Group 2 to 3 dip, caused by:
- electron is lost from a p orbital with the group 3 element, rather than an s orbital
- p orbitals are more remote so the e- is easier to remove
b) Group 5 to 6 dip, caused by:
- group 5 have a stable symmetrical arrangement of e-s
- in group 6 it is not as stable, and the orbitals are not symmetrical;increased repulsion; e- easier to remove
Is Ionisation Energy exothermic? explain your answer
NO! It is endothermic
IE requires energy from its surroundings to overcome the attractive forces of the nucleus and remove an electron
What is the trend in atomic radii down a group and whu
- increase
- there is an extra complete main level of e-
- outer electron main level is further from the nucleus
