Ionisation Energy Flashcards
Ionisation is…
Removal of one or more electrons
First ionisation energy
Energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form one mole of gaseous 1+ ions
First ionisation of oxygen
O(g) ——> O+ (g) + e-
3 factors affecting ionisation energy
Nuclear charge
Distance from nucleus
Shielding
Nuclear charge
More proteins there are in the nucleus, the more positively charged nucleus is
Stronger the attraction for electrons
Higher ionisation energy
Distance from nucleus
Attraction decreases with distance
Electron closer to nucleus will be much more strongly attracted than one further away
Shielding
As number of electrons between outer electrons and nucleus increases
Outer electrons feel less attraction to nuclear charge
Lessens pull of nucleus by inner shells of electrons
Second ionisation energy
Energy needed to remove one electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
2nd ionisation energy equation
O+ (g) ———> O2+ (g) + e-
Successive ionisation energy equation using n
(n-1)+. n+. -
X. (g) ————> X (g) + e
Within each shell, successive ionisation energies …
Increase
Why do successive ionisation energies increase
Electrons are being removed from Increasingly positive ion
Less repulsion amongst remaining electrons
———> held more strongly to nucleus
How do successive ionisation energy graphs tell you group in periodic table an element belongs to?
How many electrons are removed before first big jump
Eg 3 are removed until jumps significantly higher in ionisation so element belongs to group 3
Electronic structure prediction using graphs
Go from right to left
Count how many point before big jump
Gives oh how many electrons are in each shell starting with first
3 trends in ionisation energy
- 1st ionisation energy down a group decreases
- 1st ionisation across period generally increases
- Ionisation energy changes down group 2 + across period 3
Ionisation energy ____ across a period
Increases
Why does ionisation energy increase across period?
Number of protons increases
Stronger nuclear attraction
Ionisation energy _____ down group 2
Decreases
The drop in ionisation energy between group 2 and 3 shows _____
Sub shell structure
Drop between group 5 and 6 is due to ____
Electron repulsion
Electron repulsion
Orbitals hold 2 electrons
If only one electron is in an orbital rather than 2 which are paired
Harder to remove one alone than one in a pair
Ionisation energy decreases down group 2, why?
Each element down group 2 has extra electron shell compared to one above
Extra inner shells will shield outer electrons from attraction of nucleus
Extra shell increases distance from nucleus
Decreasing ionisation energy
