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Flashcards in Ionisation Energy Deck (17)
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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


Shielding effect

Repulsion between inner and outer shell electrons in an atom


2nd ionisation energy

Energy required to remove 1 electron from each ion in 1 mole of gaseous 1+ ion of an element to form 1 mole of gaseous 2+ ions