atomic structure - electrons Flashcards
(19 cards)
valence electrons definition
electrons in the outermost shells - typically these are involved in reactions
ground state definition
the lowest energy/most stable arrangement for electrons - influenced by electron-electron and electron-nucleus interactions
which atoms have electron electron interactions?
any atom with more than 1 electron
what is the orbital approximation?
a function made up of many different electron wavefunctions, which works for more than just 2 bodies
what is a limitation of the orbital approximation?
in hydrogen, all orbitals with the same QN n are degenerate, because orbital energy depends on QN n, and there are no electrons beyond n=1
but in multi electron atoms, this degeneracy is lifted, so orbitals with different QN l values have different energies
how does angular QN l affect orbital energy?
the lower the angular QN, the lower the orbital energy - for atoms with QN n>1
what 3 rules govern electronic configuration?
Aufbau principle
Pauli principle
Hunds first rule
outline the how the aufbau principle governs electron configuration
it states that electrons fill orbitals from the lowest energy orbital upwards
orbital energy increasing as QNs n and l increase, as following the bohr-bury rules, this is the order that they fill
why is the aufbau principle true in practise?
electron-nucleus interactions:
all electrons in an atom experience attraction of the +vely charged nucleus, Z
electron-electron interactions:
the attraction is reduced by any electrons in lower energy orbitals, which are closer to the nucleus and shield valence electrons from the nuclear charge to some extent, so these electrons experience an effective nuclear charge Zeff
give the equation for Zeff
Zeff = z-s
where z = nuclear charge
and s = shielding
how does Zeff affect valence electrons?
greater Zeff = greater stabilisation of the valence electrons
what is the trend of penetration for atomic orbitals + why is this important?
for atomic orbitals of the same shell, core penetration and orbital stability follows this trend:
ns>np>nd>nf
this forms the basis of the aufau principle, essentially most stable atomic orbitals are filled first
outline how the pauli principle governs electron configuration
states that no 2 electrons can have the same 4 QNs - each atomic orbital can only accept 2 electrons, each with a different spin QN
outline how hunds first rule governs electron configuration
states that electrons fill orbitals of the same energy to give the maximum number of unpaired electrons - as a result, this gives maximum number of parallel spins (when all have the same ms value)
why is parallel spin favourable?
if all electrons have parallel spins, there is less electron-electron repulsion that if electrons are paired which increases stability
exchange energy definition
an increase in stability provided by having pairs of parallel electrons - these electrons can be exchanged across all orbitals of the same energy level
what configuration of electrons has what spin state?
3 unpaired electrons/parallel spins = quartet spin
2 unpaired electrons = triplet spin
1 unpaired electron = doublet spin
0 unpaired electrons = singlet spin
how does exchange energy change with spin state?
going from quartet -> singlet spin, exchange energy decreases, because number of unpaired electrons decreases
the transition elements Cr and Cu are exceptions to these rules - why?
this is because its outermost orbital is the 3d orbital, which is very close in energy to the 4s orbital
their configurations should be:
Cr: [Ar] 4s2 3d4
Cr: [Ar] 4s2 3d9
but instead they adopt:
Cr: [Ar] 4s1 3d5
Cu: [Ar] 4s1 3d10
this is because it is more stable for the atoms to have fully paired/unpaired electrons
