7.2 - Ionisation Energies Flashcards Preview

OCR A Chemistry A Level - Chapter 7 > 7.2 - Ionisation Energies > Flashcards

Flashcards in 7.2 - Ionisation Energies Deck (12)
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Define 1st ionisation energy

Energy requires to remove 1 electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.


State the factors that affect ionisation energies.

Atomic Radius
Nuclear Charge
Electron Shielding


Explain how atomic radius affects ionisation energy.

Greater distance from nucleus to outer shell electrons lowers the force of attraction.


Explain how nuclear charge affects ionisation energy.

The more protons there are in the nucleus, the greater the attraction between the nucleus and outer shell electrons.


Explain how electron shielding affects ionisation energy.

Shielding effect: Repulsion between electrons in different inner shells repelling outer shells.
Shielding reduces the net attractive forces between nucleus and outer shell electrons.


Why are successive ionisation energies higher than prior ones?

Once an electron is removed, per electron there is more nuclear attraction as the ratio of proton:electron increases, and the atomic radius (if the successive ionisation is the next shell) is smaller, increasing ionisation energy.


Define second ionisation energy.

Energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form 1 mole of 2+ gaseous ions.


What can successive ionisation energies give you information about?

No. of electrons in the outer shell
Group of element in periodic table
Identity of element


What are the trends of first ionisation energies?

General increase in ionisation energy across a period

Sharp decrease in ionisation energy from end of first period to beginning of next


What are the 1st ionisation energy trends down a group?

First ionisation energy decreases due to increase in atomic radius - (more electrons per element in inner shells increasing shielding effect)
- Outer electron ends up being further from the nucleus lowering attraction


What are the 1st ionisation energy trends across a period?

General increase in 1st ionisation energy (Periods 1-3)
- Increase in nuclear charge due to increase in atomic number.
- Shielding effect remains the same, nuclear attraction increases, atomic radius decreases. 1st ionisation energy increases.


During period 2 there are drops in ionisation energies between Berylium and Boron, and Nitrogen and Oxygen. Explain why

Boron marks the start of 2p electron filling
- 2s sub shell is filled for Be
- 2p electron in Boron has higher energy than Berylium and is easier to remove.

Oxygen marks the beginning of 2p electron pairing
- In both N & O, the highest energy electron is the 2p sub shell
- There is a 2px2 in O and only 2px1 in N, the 2 electrons in 2px repel one another making it easier to remove lowering the ionisation energy.