1. 3ionisation energies Flashcards
first ionisation energy
the fisrt ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
first ionisation energy of oxygen
1314kj
atoms and ions fact
you must use the gas symbol as ionisation energy are measured for gaseous atoms
you refer as 1 mole of atoms
the lower the ionisation energy the easier it is to form positive ions
factors that effect ionisation energy
nuclear charge
distance from nucleus
shielding
nuclear charge
the more protons there are in the nucleus the more positively charged the nucleus is and the stronger the nuclear force of attraction for the electrons
distance from nucleus
attraction falls off rapidly with distance. an electron close to the nucleus will be much more strongly nuclear attracted than one further away
shielding
as the number of electrons between the outer electrons and nucleus increases the outer electrons would fell less attraction to the nucleus. This lessens the pull of the nucleus thanks to the inner shells. This is known as shielding
another name for energy
enthalpy
nuclear charge
you can only see the effect of nuclear charge on ionisation energy if you compare atoms with outer shell electrons the same distance from the nucleus and with equal shielding effects. that only really happens with elements that are in the same period of the periodic table
second ionisation energy
this is the energy required to remove an electron of 1 mole of gaseous 1+ ions
second ionisation energy energy
like the first one the value of energy depends on the nuclear charge, distance and shielding.
the energy is greater than the first one as the electron being removed is from a positive ion. the elctron configuration of the atom will also play a role in how much larger the second ionisation energy is than the first.
third ionisation energy
this will be greater than the second as there is a greater attraction between and 2+ ions and 1+ ions with its electrons
example of ionisation
the first electron removed from lithium comes from the second shell 2s 1 .
the second electron removed would be from the fisrt shell so the second electron would face a stronger nuclear attraction.
the second electron would have no sheilding therefore would be more attracted
successive ionisation energy
you can remove all of the electrons in the nucleus however each time you remove an electron the larger the successive energy is.
x (n-1)+ —–> x n+ + e -
group 2 ionisation energy
the first ionisation energy decreases down the group.
this provides evidence that electron shells do exist, if each element in group 2 has one more shell than the one above then the extra shell will shield the other shells from the nuclear attraction from the nucleus.
distance and group 2 energy
distance decreases energy as well
ionisation across periods
if you move across the period the general trend shows that ionisation energy increases.This is because as the number of proton’s increases then the strengh of the nuclear attraction increases also.
extra electrons
the extra electrons are at roughly the same energy level even if the outer electrons are in different orbital types. This means that there’s generally little extra shielding effect or extra distance to lesen the attraction from the nucleus.
group 2 and 3
aluminium outer electron is in 3 p orbital rather than a 3s . 3p has a slightly higher energy than the 3s orbital, so the electron is on average to be found further from the nucleus.
3p as extra shielding provided from the 3s orbital
these factors together can override the effect of increased nuclear charge , resulting in the ionisation energy dropping slightly. This pattern in ionisation energies provides evidence for the theory of electron sub shell
group 2 and 3 factors
these factors together can override the effect of increased nuclear charge , resulting in the ionisation energy dropping slightly. This pattern in ionisation energies provides evidence for the theory of electron sub shell
group 5 and 6
the drop between group 5 and 6 is due to electron repulsion.
group 5 and 6 example
the shielding is identical in the phosphorus and sulfur and the electron is being removed from an identical orbital.
in phosphorus’s case the electron is being removed from a singly occupied orbital. but in sulfur the electrons is being removed from an orbital containing two electrons
group 5 and 6 reasons for drop
the repulsion between two electrons in an orbital means
the repulsion between two electrons in an orbital means
that electrons are easier to remove from shared orbital orbital . it is more evidence for electronic structure model.
ionisation energy and shell structure
if you know the successive ionisation energies of an element you can work out the number of electrons in each shell of the atom and which group the element is in. a graph of successive energies provides evidence the shell structure of atoms
what happens within each shell
the successive ionisation energies increases
this is because the electron is being removed by an increasingly positive ion
why does the successive ionisation energies increases
this is because there’s less of a replusion amongst the remaining electrons so they’re held more strongly by the nucleus.
why is there a sometimes a big jump when it comes to successive ionisation
The big jump in ionisation energy happens when a new shell is broken into. an electron that is closer to the nucleus.
