Ionisation Energy Flashcards
What are 3 factors affecting the first ionisation energy?
Atomic radius
Number of protons
Shielding
What is meant by the first ionisation energy? [2 marks]
The energy required to REMOVE 1 electron from each atom in 1 mole of GASEOUS atoms to form 1 mole of GASEOUS ions.
What are the trends in first ionisation energy…
a) Down the group
b) Across a period
a) Decrease down a group
b) GENERAL increase across a period (a few exceptions)
State and explain the trend in first ionisation energies down a group [3 marks]
1 = Down a group, first ionisation energies decrease.
2 = This is because the atomic radius increases and outer electrons are more shielded and further away from the nucleus.
3 = So outer electrons experience a weaker attraction to the nucleus.
4 = So less energy is required to remove an electron.
Explain the general trend in first ionisation energies across a period [3 marks]
1 = Across a period, there is a GENERAL increase in first ionisation energies.
2 = This is because the nuclear charge increases as there are more protons, and the shielding of outer electrons stays roughly the SAME.
3 = So outer electrons experience a stronger attraction to the nucleus.
4 = So more energy is required to remove an electron.
State and explain which element, sodium or potassium, has a lower first ionisation energy. [3 marks]
Potassium has a lower ionisation energy than sodium. [1]
This is because potassium’s outer electron is more shielded and further away from the nucleus. [1]
So, compared to sodium’s, potassium’s outer electron experiences a weaker attraction to the nucleus. [1]
Requires less energy to remove an electron from potassium.
State and explain which element, sodium or magnesium, has a higher first ionisation energy. [3 marks]
Magnesium has a higher ionisation energy than sodium. [1]
This is because Mg has a higher nuclear charge than Na and both atoms’ outer electrons have roughly the same shielding. [1]
This means that Mg’s outer electrons experience a stronger attraction to the nucleus than Na’s. [1]
Requires more energy to remove an electron from Mg.
Which elements are anomalies in the general increase trend in ionisation energy? What explanation is used for each?
Magnesium & Aluminium - sublevel is further away
Boron & Beryllium - sublevel is further away
Sulfur & Phosphorous - paired vs unpaired
Selenium & Arsenic - paired vs unpaired
Explain the anomalous trend in Aluminium and Magnesium’s ionisation energy [4 marks]
Aluminium’s first ionisation energy is lower than Magnesium’s. [1]
Mg’s electron is removed from the 3s sublevel, whereas Al’s electron is removed from the 3p sublevel. [1]
The 3p sublevel in Al is further away from the nucleus and also shielded by aluminium’s 3s electrons. [1]
So there’s a weaker attraction between outer electrons and nucleus in Al. [1]
So it requires less energy to remove an electron from an Al atom.
Explain the anomalous trend in Sulfur and Phosphorous ionisation energy [3 marks]
Sulfur’s first ionisation energy is lower than Phosphorus. [1]
The electrons in Phosphorous 3p sublevel are UNPAIRED, whereas Sulfur has a pair of electrons in one of its 3p orbitals. [1]
Paired electrons repel each other more than unpaired electrons, so it requires less energy to remove an electron from a Sulfur atom. [1]
Explain the anomalous trend in Boron and Beryllium’s ionisation energy [3 marks]
Boron’s first ionisation energy is lower than Beryllium’s [1]
The electron in Beryllium is removed from the 2s sublevel, whereas Boron’s electron is removed from the 2p sublevel. [1]
The 2p sublevel is further away from the nucleus and is shielded by Boron’s 2s electrons. [1]
So, it requires less energy to remove an electron from a boron atom.
Explain the anomalous trend in arsenic and selenium’s ionisation energy [3 marks]
Selenium’s first ionisation energy is lower than Arsenic’s [1]
Arsenic only has UNPAIRED electrons in its 4p sublevel, whereas Selenium has a pair of electrons in it’s 4p sublevel. [1]
Paired electrons repel each other more than unpaired electrons. [1]
So, it requires less energy to remove an electron from a Selenium atom
What are the options to talk about when explaining anomalies ionisation energy?
> Whether the electron is removed from an orbital further away from the nucleus
E.G. 3p compared to 3s
> Whether the electrons in the SAME orbital are paired or unpaired.
E.G. one could have 1 1 1, and the other could have ⥮ 1 1
