Ionisation Energy Flashcards
Ionisation energy
Measure of how easily an atom loses electrons to form cations
1st ionisation energy
Energy required to remove 1 electron from each atom in 1 mole of gaseous atoms of an element to form 1 mole of gaseous 1+ ions
Na(g) => Na(+,g) + e-
Factors affecting ionisation energy
Atomic radius
Nuclear charge
Electron shielding
Atomic radius on ionisation energy
Greater distance between nucleus and outer electrons, less nuclear attraction, easier to remove 1 electron
Nuclear charge on ionisation energy
More protons in the nucleus, greater attraction between nucleus+outer electrons
Electron shielding
Negatively charged electrons
Inner shell electrons repel outer shell electrons
Shielding reduces attraction between nucleus and outer electrons, easier to remove electrons
Successive ionisation energies
Has as many ionisation energies as there are electrons
Once 1 electron removed, remaining electrons pulled closer to nucleus, nuclear attraction increases
Relationship between successive ionisation energies and shells
Large increase between 2 ionisation energies suggests that electron was removed from a different shell, closer to nucleus, less shielding
What can we find out from successive ionisation energies?
No of electrons in outer shell
Group of element in periodic tabel
Identity of an element
Trends in ionisation energies
Provide important evidence for existence of shells and sub shells
Trends in ionisation energy down a group
As no of shells increases Atomic radius increases Shielding increases Nuclear attraction on outer electrons decreases 1 IE decreases down group
Trends in ionisation energy across a period
As no of electrons increase Nuclear charge increases Same shell, similar shielding Nuclear attraction increases Atomic radius decreases 1st IE increases
Sub shell trends in 1st IE
Falls in 2 places in each period
Linked to p and s shells
Beryllium, Boron
Nitrogen, Oxygen
Sub shell trends in Beryllium and Boron
2p sub shell in boron, higher energy than 2 s sub shell in beryllium
2p electron in boron easier to remove than 1 2s electron in beryllium
Sub shell trends in nitrogen and oxygen
Nitrogen and oxygen have highest energy electrons in the 2p subshell
Oxygen, paired electrons in one of the 2p orbitals repels one another, making it easier to remove an electron from an oxygen than a nitrogen atom
In nitrogen, equal repulsion
In oxygen , paired electrons repel
