Atomic Structure: Electron Configuration - Ionisation Energies Flashcards
1
Q
First Ionisation Energy
A
- The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of +1 ions
- X(g) → X+(g) + e‒
2
Q
Second Ionisation Energy
A
- The second ionisation energy involves the removal of a second electron
- X+(g) → X2+(g) + e‒
3
Q
Factors Affecting Ionisation Energies
A
- A high ionisation energy means there’s a high attraction between the electron and the nucleus, so more energy is needed to remove the electron
• Nuclear charge
- The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons
• Distance from the nucleus
- Attraction falls off very rapidly with distance
- An electron close to the nucleus will be much more strongly attracted than one further away
• Shielding
- As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction to the nucleus
- This lessening of the pull thanks to the inner electrons is called shielding
4
Q
Explain drastic increases in ionisation energies
A
- Large jumps in the ionisation energy reveal where electrons are being removed from a lower energy principal energy level
- Also less shielding makes the electron harder to remove
- Successive ionisation energies give us evidence for principal energy levels
5
Q
Ionisation Energy Across a Period
A
• Across a period, there is a general increase in the ionisation energies
- The number of protons increase, so there is a stronger nuclear attraction
- The shielding effect is similar as the outer electrons are at roughly the same energy level
6
Q
Ionisation Energy Down a Group
A
• The first ionisation energy always decreases down a group
- The nuclear charge increases down the group
- But the electrons are being removed from successively higher principal energy levels, which are on average:
- Further from the nucleus
- More shielded by inner electron shells
- And are therefore less attracted to the nucleus