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20 Cards in this Set
- Front
- Back
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What happens in ionisation? |
An electron is removed from the outer shell of an atom. |
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What does ionisation create? |
Positive ions (cations) |
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What is needed in ionisation? |
Energy is needed to overcome nuclear attraction between the nucleus and electrons. |
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What is this energy called? |
The ionisation energy |
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What is the first ionisation energy? |
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. |
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What must be changed for ionisation to occur? |
A solid must be vaporised to turn it into a gas. |
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Give an example of a first ionisation energy equation. |
Na (g) ---> Na+ (g) + e-
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Which three factors affect ionisation energy? |
Nuclear charge
Electron shielding Atomic radius |
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How does nuclear charge affect ionisation energy? |
The more protons in the nucleus, the greater its nuclear charge; hence, there will be a stronger nuclear attractive force between the nucleus and electrons. Consequently, a higher nuclear charge means more energy is needed to remove the electron. |
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How does atomic radius affect ionisation energy? |
Atomic radius is the distance between the nucleus and the outermost electron. The further away the outermost electron is from the nucleus, the weaker the nuclear attractive force. Therefore, less energy is needed to remove the electron. |
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How does electron shielding affect nuclear attractive force? |
This is the number of electron shells between the nucleus and the outermost electron. The more shielding there is, the less energy is needed for ionisation. |
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How does first ionisation energy change as you go down the group? |
As you go down the group, it decreases. This is because electron shielding and atomic radius increases and this outweighs the increase in nuclear charge. Therefore, nuclear attraction decreases so ionisation energy gets lower. |
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How does first ionisation energy change as you go across a period? |
As you go from left to right, it increases. This is because electron shielding stays the same, atomic radius decreases slightly and nuclear charge increases. As nuclear charge increases, nuclear attraction increases, so more energy is needed for ionisation. |
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What are the exceptions to this rule? |
Beryllium and Boron Nitrogen and oxygen Magnesium and aluminium Phosphorous and sulphur |
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Why is there a blip between boron and beryllium? |
Beryllium needs more ionisation energy than it should because its outer subshell is full, making it more stable. Boron needs less ionisation energy than it should because it's outer shell is unfilled, so it's less stable and it's further away from the nucleus than beryllium by a subshell. |
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Why is there a blip between nitrogen and oxygen? |
Oxygen has one pair of electrons in the 2p subshell which nitrogen doesn't. This pair repel each other, meaning it's easier to remove one of these electrons and ionisation energy is lower for oxygen. |
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Why are magnesium and aluminium outliers? |
Magnesium has the highest ionisation energy. This is because, although they have the same number of shells, magnesium's outer electron is in an s orbital, whilst aluminium's is in a p orbital. Therefore, aluminium has a larger atomic radius. Hence, aluminium has a lower ionisation energy even though it has a higher nuclear charge.
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Why are phosphorous and sulphur outliers? |
Phosphorous has a higher ionisation energy. This is because, Sulphur has an outer p4 orbital, whilst phosphorous has an outer p3 orbital. The extra electron repels the other making it easier to lose. This means sulphur has a low ionisation energy even though its nuclear charge is larger. |
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Which element has the highest ionisation energy? |
Helium, because it has the same atomic radius as hydrogen and no sheilding, but it's nuclear charge is larger by 1. |
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Which element has the lowest ionisation energy? |
Caesium |
