Section 2 - Ionisation Energy Flashcards
What is the meaning of the ‘first ionisation energy’?
The energy you need to remove the first outer electron
How is an electron taken out of its electron shell?
You need to overcome the attraction between the negative electron and the positively charged nucleus. To do this, you have to add energy, so the ionisation energy is always a positive number
What are three things that can affect the ionisation energy? (3)
1) Nuclear charge
2) Distance from the nucleus
3) Shielding
How does nuclear charge affect ionisation energy?
The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons.
How does distance from the nucleus affect ionisation energy?
Attraction decreases with distance. An electron close to the nucleus with be more strongly attracted than one further away.
How does shielding affect ionisation energy?
Electrons in shells closer to the nucleus can stop the outer electrons from feeling the full force of the nuclear charge. The inner electrons are said to shield the outer electrons from the nucleus. More inner electrons mean more shielding. More inner electrons means more shielding, so a weaker attraction for the outer electrons and a lower ionisation energy.
How does shielding affect ionisation energy?
Electrons in shells closer to the nucleus can stop the outer electrons from feeling the full force of the nuclear charge. The inner electrons are said to shield the outer electrons from the nucleus. More inner electrons mean more shielding, so a weaker attraction for the outer electrons and a lower ionisation energy.
Why does ionisation energy decrease down a group?
This is because as you go down a group, each element has one more electron shell than the one above - so the distance between the nucleus and the outer shell increases. There will also be more shielding from the larger number of inner electrons. So overall, going down a group the attraction between the nucleus and the outer electron decreases.
Why does ionisation energy generally increase across a period?
There are more protons in the nucleus so there’s a higher nuclear charge. Electrons are also going into the same shell, so the distance from the nucleus and the amount of shielding by inner electrons doesn’t change much. So overall, the attraction between the nucleus and the electrons increase.
