ionisation energy Flashcards
define first ionisation energy of a substance
The energy required to remove one moles of electrons from about a mole of atoms of an element to form one moles of gaseous ions therefore.
what conditions are ionisation energies measured in?
standard conditions, 298K and 101kPa
what are the units of IE?
kilojoules per mole (kJ mol^-1)
what do ionisation energies showcase?
periodicity - a trend across a period of the periodic table therefore
what are the differences in ionisation energy between group 1 metals and noble gases?
group 1 metals do have a relatively low ionisation energy whereas noble gases do have relatively higher IES
what are the factors affecting the size of the first ionisation energy?
- nuclear charge size.
- distance of the outer electrons and the nucleus
- shielding effect of the therefore inner electrons and the spinpair repulsion.
how does the sizing of the nuclear charge affect ionisation?
the more protons in the so nucleus, the more positively charged the nucleus is and the stronger the attraction is between the outer electron and nucleus.
how does the distance between the nucleus and outer affect ionisation?
An electron closer to the nucleus will be more strongly attracted than one further away.
how does shielding affect ionisation?
as the number of electrons between the outer electrons and the nucleus increases, the outer electrons are feeling less attraction towards the nuclear charge.
shielding is the lessening of the pull of the nucleus by the therefore inner shells of electrons.
what it means if something has a high ionisation energy?
a high attraction between the electron and the nucleus therefore more energy is required to remove the electron.
do first ionisation energy increase across a period or a group?
across a period. It becomes harder to remove an electron as you move across a period because a greater amount of energy is required.
do the first ionisation energy decrease across a period or a group?
group
Why does the first ionisation energy increase across a period due to nuclear charge?
across a period the therefore so nuclear charge increases due to increase proton numbers. all the electrons are at roughly the same energy level even if the outer electrons are in different so orbital types.
Why does the first ionisation energy increase across a period due to atomic radius?
as a result of increased nuclear charge, the atomic radius (distance between nucleus and outer electron) of atoms decreases because the outer shell is pulled closer to the nucleus, so the distance between the nucleus and the outer electrons decrease therefore.
Why does the first ionisation energy increase across a period due to shielding?
The shielding by the therefore so shells of inner electrons remains constant as electrons are being added to the exact therefore same shelli.
explain the dips in the ionisation energy trend between groups 2 and 3 in period 2
there is a slight decrease in IE1 between berillyum and boron as the fifth electron in therefore boron is in the 2p subshell, which is further away from the nucleus compared to the 2s subshell of berillyum and hence there is greater electron shielding and distance between the outer electron and nucleus therefore a decrease in strength of the electrostatic forces attraction.
(Subshell structure therefore)
explain the dips in the ionisation energy trend between groups 2 and 3 (period 3)
magnesium to aluminium.
aluminiums outer electron is in a 3p orbital rather than a 3s therefore so. The 3p orbital had a slightly higher energy than the 3s orbital, so the electron is, on average, to be further from the nucleus.
the 3p orbital has additional shielding provided by the 3s2 electrons both these factors are strong enough to override the effect of nuclear charge, resulting in the ionisation energy dropping.
provides evidence for theory of electron sub-shells.
explain the dips in the ionisation energy trend between groups 5 and 6
the shielding is identical in the phosphorus and sulfur atoms and the electron is being removed from an identical orbital.
in phosphorus case, the electron is being removed from a singlyoccupied orbital. But in sulfur, the electron is being removed from an orbital containing two electrons.
the repulsion between the electrons in an orbital means that electrons are easier to remove from shared therefore orbitals so.
explain the decrease in ionisation energy between last element in a period and the therefore first in another
large decrease because there is an increased distance between the nucleus and the outer electrons as you have added another therefore shell.
there is increased shielding by inner electrons because of the outer shells.
these two factors outweigh the increased nuclear charge.
explain the decrease in ionisation energy down a group as a result of the nuclear charge.
number of protons in the atom increases so the therefore so nuclear charge increases, yet shielding and distances outweigh this factor however.
explain the decrease in ionisation energy down a group as a result of atomic radius therefore
the atomic radius increases because you are adding more shells of electrons, therefore making the atoms bigger. the outer electrons further from the nucleus so the nucleus’s attraction will be greatly reduced.
explain the decrease in ionisation energy down a group as a result of shielding
as a group goes downwards each element has an extra electron shell compared to the element above, therefore shielding pf the outer electrons from the attraction of the nucleus by the extra inner shells increases
define the second ionisation energy
The second ionisation energy (IE2) is the energy required to remove the second mole of electrons from each +1 ion in a mole of gaseous +1 ions, to form one mole of +2 ions
define the third ionisation energy
The third ionisation energy (IE3) is the energy required to remove the third mole of electrons from each +2 ion in a mole of gaseous +2 ions, to form one mole of +3 ions
what are the sequences of these ionisation energies known as?
successive ionisation energies.
you can remove all the electrons from an atom, leaving the nucleus.
within each shell do successive ionisation energies increase or decrease?
increase
why do successive ionisation energies increase?
because once the outer electron of an atom has been removed, a positive ion forms. removing an electron coming from a positive ion is more difficult compared to from a neutral atom
As more electrons are removed, the attractive forces increase between the nucleus and outer electron due to decreasing shielding and an increase in the proton to electron ratio. there is les repulsion amongst the remaining electrons.
however the increase in ionisation energy is dependent on electron configuration therefore.
in a graph showing successive ionisation energies, what do small jumps represent?
change of subshell
how can you figure out the group number from a successive ionisation energy graph?
count electrons removed before the first big jump
analyse the graph for the element calcium and its effect on successive ionisation energies (the first electron)
The first electron removed has a low IE1 as it is easily removed from the atom due to the spin-pair repulsion of the electrons in the 4s orbital
calcium has 20 electrons, electron configuration is
1s2 2s2 2p6 3s2 3p6 4s2
analyse the graph for the element calcium and its effect on successive ionisation energies (the second electron)
The second electron is more difficult to remove than the first electron as there is no spin-pair repulsion
analyse the graph for the element calcium and its effect on successive ionisation energies (the third electron)
The third electron is much more difficult to remove than the second one corresponding to the fact that the third electron is in a principal quantum shell which is closer to the nucleus (3p)
Removal of the fourth electron is more difficult as the orbital is no longer full, and there is less spin-pair repulsion
Similar to fifth therefore so.
what does a successive ionisation energy graph show?
The graph shows there is a large increase in successive ionisation energy as the electrons are being removed from an increasingly positive ion
what can successive ionisation energy data be used for?
- predicting or confirming the therefore electron configuration of elements.
- confirm the number of electrons in the outer shell of an element
- deduce a Group an element belongs to in the periodic table.
sodium
For sodium, there is a huge jump from the first to the second ionisation energy, indicating that it is much easier to remove the first electron than the second
Therefore, the first electron to be removed must be the last electron in the valence shell thus Na belongs to group I
The large jump corresponds to moving from the 3s to the full 2p subshell
Na 1s2 2s2 2p6 3s1
