Ionisation Flashcards
First ionisation energy
The energy required to remove 1 electron from every atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Second ionisation energy
Energy required to remove 1 electron from every ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Successive ionisation energies
What occurs when more electrons are removed from an atom, requires more energy each time because of increased electrostatic attraction between the electron and nucleus also less shielding
When writing ionisation equation
(g) state symbol
Only 1 electron is removed
Charge increases
The number of successive ionisation energies is the same as the charge formed on positive ion
How does the electron in ionisation energy get removed?
The energy supplied is used to overcome the electrostatic attraction between negative electron and positive nucleus and remove electron
What does the ionisation energy depend upon?
How strong the electrostatic attraction between the nucleus and electron is
Strong attraction requires more energy to overcome
What happens if the electrostatic attraction between the ionising electron and nucleus is strong?
Then the ionisation energy will be large because more energy is required to overcome this attraction
What factors affect the electrostatic attraction thus the ionisation energy?
Shielding
Number of protons
Size of atom
SNS
(Spin sometimes of the electron)
Shielding
A decrease in the nuclear charge experienced by an outer shell electron caused by electron-electron repulsionbetween the outer shell electron and electrons from adjacent quantum shells
How does shielding have an effect on ionisation energy?
With increased number of electrons there is more repulsion between them
So shields and reduces electrostatic attraction electron has to the nucleus
So ionisation energy is smaller
Nuclear charge
The positive charge produced by protons on the nucleus
Causes electrostatic attraction between electrons
How does nuclear charge have an effect on ionisation energy?
The greater number of protons means greater nuclear charge
So greater electrostatic attraction between the electron and nucleus
So ionisation energy is greater, requires more to overcome
Size of atom/ distance electron from nucleus
When there are more internal shells the electron is further away
And electrostatic attraction decreases sharper if it’s further away so reduces ionisation energy needed to remove electron
How does distance of atom/ distance electron is from nucleus affect ionisation energy?
If there are less internal shells between the electron and nucleus
Then electrostatic attraction increases sharply because the electron is closer
So higher ionisation energy
Sudden jump in ionisation energies of an atom of 1 element
When the electron is in a shell closer to the nucleus
There is a decrease in distance of electron to nucleus
So increase in electrostatic attraction = increase ionisation energy
Ionisation energy trends across periods
ACROSS the period the ionisation energy INCREASES
The number goes up so more energy is required to remove electron
Why does ionisation energy INCREASE ACROSS the period?
Increased electrostatic attraction between nucleus and electron
Shielding had little effect, which reduces ie:
But nuclear charge increases thus the radius decreases so more electrostatic attraction which counteracts shielding
Why does the atomic radius decrease across the period?
Even though there is no increase in shells
The more protons have greater nuclear charge
So electrons are pulled closer to the nucleus decreasing distance between outer shell and nucleus
Ionisation energy trend down the group
Going down a group the ionisation energy decreases
So less energy is needed to overcome the electrostatic attraction
Why does ionisation energy DECREASE going DOWN the group?
One more quantum shell
And so the electron is at a higher level than the electron for element above
As a result IE decreases
But also experiences more shielding due to electron-electron repulsion as there are more electrons
Furthermore the electron is at a further distance
These overcome increase in nuclear charge.
Does the increase in atomic number affect the ionisation trends going down the group?
It would increase ionisation energy because of increased nuclear charge
But the increase in shielding and distance outweigh this thus the ionisation energy decreases
Be and B electron configurations
Be = 1s²2s²
B = 1s²2s²2p¹
Anomalies in the ionisation energy periodic table trends: Be to B
From Be to B the ionisation energy decreases
Because the singular 2p electron is in a higher energy sub shell than 2s
So it’s easier to remove the outer energy in 2p thus less energy required for B so lower ionisation energy
N and O electron configurations
N = 1s²2s²2p³
O = 1s²2s²2p⁴
Anomalies in ionisation energy trends in periodic table trends: N to O
There is a decrease in ionisation energy between N and O
Because in the 2p shell of N
The 3 electrons are unpaired
Whereas in 2p of O, 2 electrons are paired
The repulsion between electrons in O makes it easier to remove = decreased ionisation energy
Which electron is removed from first then successive ionisation energies?
Electrons in the highest energy levels removed first
Them to the lower energy levels
Which is why electron from 4s is lost before 3d
What is the evidence that shows electrons occupy shells of different energy levels?
Shown in atomic emission spectra
What is atomic emission spectra and how does it work?
A technique where:
Gaseous atoms are given energy (heating etc)
Theelectrons move to a higher energy level then return, emitting electromagnetic radiation
How does atomic emission spectra prove that atoms have different energy levels?
When returning to original energy level, they emit electromagnetic radiation
Which is seen on a spectrum
But only specific frequencies are emitted not a continued spectrum
So perhaps there are fixed energy levels (as shells) rather than as continuous increasing
Why is there an increase in magnitude of successive ionisation for one atom?
Because as electrons are removed, the repulsions between electrons are decreasing
So the electrons are at lower energies
Meaning more energy is required to remove them from the orbital (increase in ionisation energy)
Where does electron-electron affect?
between 2 electrons in the same orbital
Between 2 electrons in the same shell but diff orbital
Between electrons in adjacent shells
Is 4s lost before 3d?
Yes because electrons are lost from high energy orbitals which is 4s
Why is 4s filled before 3d?
Because 3d is quite compact, so filling electrons in 3d first increases repulsion, so electrons are filled in 4s first
