Ionisation Energy Flashcards
What is the first Ionisation Energy
The first ionisation energy of an element is the energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
What type of reaction is Ionisation energies
Endothermic reactions
Why are ionisation energy endothermic reactions
Negative electrons are held in their electron shells by strong electrostatic forces of attraction with the positively charged nucleus.
Therefore more energy must be supplied than is released in order to break this attraction and therefore remove one electron from a gaseous atom
What is successive ionisation energies
A measure of the amount of energy required to remove each electron in turn.
What are the 3 factors affecting ionisation energy
- Atomic Radius
- Nuclear Charge
- Electron Shielding
How does it affect ionisation energy
Atomic Radius
The greater the distance between nucleus and outer e– the less nuclear attraction
How does it affect ionisation energy
Nuclear Charge
More protons in nucleus of atom, the greater the attraction between the nucleus and the outer e—
How does it affect ionisation energy
Electron Shielding
Electrons are negatively charged and so the inner-shell e– repels the outer shell e—.
This repulsion reduces attraction between nucleus and outer electrons.
Trends in ionisation energy in groups
The first ionisation energy decreases down the group.
Why does the ionisation energy decrease down the group
As you go down the group:
* No. of electron shells increases therefore atomic radius increases.
* More inner shells so shielding increases
* Nuclear attraction on outer electrons decreases.
Nuclear charge also increases, its effects are outweighed by the increased radius, and to a lesser extent, the increased shielding.
Trends in ionisation energy in Periods
first ionisation energy increases across a period
Why does the ionisation energy increase across the period
As you go across a period:
* Nuclear charge increases
* Same no. of shell; similar shielding
* Nuclear attraction increases.
* Atomic radius decreases.
What are the 2 anomalies in period 2
A fall from Be to B and from N to O.
What does the fall from Be to B show.
the start of filling the 2p sub-shell.
Why is there a fall from Be to B.
The 2p sub-shell in B has a higher energy than the 2s sub-shell in Be.
Therefore, in B the 2p electron is easier to remove than one of the 2s electrons in Be.
Why is there a fall from N to O.
In O the paired electrons in one of the 2p orbitals repel one another making it easier to remove an electron from an O atom than a N atom.
