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Description
Flashcards by Bee Brittain, updated more than 1 year ago
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Created by Bee Brittain
over 8 years ago
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| Question | Answer |
| What is Ionisation energy? | Ionisation energy measures how easily an atom loses electrons to form positive ions |
| Define the term, 'First Ionisation Energy' | First Ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions |
| Factors that affect ionisation energy | - Atomic Radius - Nuclear Charge - Shielding |
| Atomic Radius | The greater the distance between the nucleus and the outer electrons, the less the nuclear attraction. The force of attraction falls off sharply with increasing distance, so atomic radius has a large effect. |
| Nuclear Charge | The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus and the outer-shell electrons. |
| Shielding | Electrons are negatively charged, so inner-shell electrons repel outer-shell electrons. This repulsion, called the shielding effect, reduces the attraction between the nucleus and the outer-shell electrons. |
| Two key patterns of first ionisation energy in the first 20 elements in the periodic table. | 1) A sharp DECREASE in first ionisation energy between the end of one period and the start of another. He --> Li, Ne --> Na, Ar --> K 2) A general INCREASE in first ionisation energy across each period. H --> He, Li --> Ne, Na --> Ar |
| Trend in first ionisation energy down a group | First ionisation energies decrease down a group. This is because although nuclear charge increases, Its effect it out-weighed by the increasing atomic radius as there are more shells and to a lesser extent, shielding also increases. |
| Trend in first ionisation energy across a period | First ionisation energy shows a general increase across periods, however it does fall in two places. These falls also occur in the same positions on each period. This is due to sub-shells, their energies and how orbitals fill with electrons. |
| Trend in first ionisation energy across a period - Period 2 | Two falls in period two. 1 between Be to B and the other between N to O. Apart from the two falls there is a general increase. |
| Trend in first ionisation energy across a period - Period 2, the fall from Be to B | The fall from Be to B marks the start of filling the 2p sub-shell. The 2p sub-shell has a higher energy than the 2s sub-shell. Therefore in Boron, the 2p electron is easier to remove than one of the 2s electrons in Be. So, the first ionisation energy of B is < the first ionisation energy of Be. |
| Trend in first ionisation energy across a period - Period 2, the fall from N to O | This fall marks the start of electron pairing in the p-orbitals of the 2p sub-shell. In N and O the highest the highest energy electrons are in a 2p sub-shell. In O, the paired electrons in one of the 2p orbitals repel one another, making it easier to remove an electron from nitrogen than oxygen. Therefore first ionisation energy of O < the first ionisation energy of N |
| Successive Ionisation Energies | If there is a large increase suddenly in successive ionisation energies, it suggests that the latest electron was removed from a shell closer to the nucleus, with less shielding. |
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