Ionisation Energy QA, FA Flashcards
State the definition of ‘ionisation energy’
Ionisation energy is the energy required to remove one mole of electrons from one mole of a gaseous atom
What is the equation for the first ionisation energy of Mg?
Mg(g) → Mg⁺(g) + eˉ
Why is the second ionisation energy higher than the first?
Because once you have removed the first electron, you are left with a positive ion (cation) and a higher nuclear charge. Trying to remove a negative electron from a positive ion is going to be more difficult than removing it from an atom as you have to overcome stronger electrostatic forces.
What is the equation for the second ionisation energy of Mg?
Mg⁺(g) → Mg²⁺(g) + eˉ
What is ionisation energy measured in?
kJmolˉ¹
What are successive ionisation energies?
The energy values for removing the second and subsequent electrons from an atom in its gaseous state.
What do the patterns in the first ionisation energies across a period provide evidence for?
The existence of electron sub-shells
Why do the first ionisation energies decrease going down Group 2?
Because the number of electron shells between the outer electron and the nucleus is increasing; the electron shells shield the outer electron from the attraction of the nucleus. Also because the radius of each atom is increasing as you go down the group so the distance between the outer electron and the nucleus is increasing.
What do the patterns in the first ionisation energies down a group provide evidence for?
The existence of electron shells.
Why do the first ionisation energies increase going across a period?
Because the number of protons increases across a period, which means that the nuclear charge also increases, leading to a higher electrostatic force of attraction between the negative electron and positive nucleus.
Why is there a dip in ionisation energy between magnesium and aluminium going across Period 3?
Because the outer electron in aluminium is in a p orbital. This is higher in energy than the outer electron in magnesium, which is in an s orbital, so less energy is needed to remove it as it is further away from the nucleus.
Why is there a dip in ionisation energy between phosphorus and sulphur going across Period 3?
Because the 3p electrons in phosphorus are all unpaired whereas, in sulphur, two of the 3p electrons are paired. There is some repulsion between paired electrons in the same sub-shell which reduces the force of their attraction to the nucleus, so less energy is needed to remove one of these paired electrons than is needed to remove an unpaired electron from phosphorus.
