1st John Flashcards
how is the periodic table set out
order of atomic number
number of protons
what atoms in the periodic table are electronically similar
atoms in the same group
theyre chemically similar
group 18
noble gases
group 1
alkali metals
group 2
alkali earth metals
main group elements
outer shells consist of s and p orbitals
s or p block elements
d metals
partially full d orbital metals.
centre of periodic table
f metals consist of
lanthanides (4f)
actinides (5f)
bottom two rows
what can the schrodinger equation not do
find solutions for multi electron systems
what do we do bc the schrodinger cant find solutions to multi electron systems
we apply the hydrogen stuff to multi electron systems
what do we need to know when applying hydrogen to multi electron systems
same quantum numbers are used
orbitals have the same shapes(radial and angular wave functions)
radial functions are similar to hydrogen (depend on n and l tho)
pauli exclusion principle
electrons must have opposite spins
no 2 electrons in an atom can have the same 4 quantum numbers
n, l, ml, ms
aufbau principle
electrons are filled from lowest energy to highest energy
we remove from highest energy to lowest energy
hunds first rule
for degenerate orbitals, electrons must be added to different degenerate orbitals with parallel spins.
eg: fill in the 3 2p orbitals with 1 electron each parallel.
parallel spins are more stable as they minimise coloumbic repulsion
what does degenerate mean
the same in energy
what does the energy in H depend on
the principle quantum number
n
what does the energy in multi electron systems depend on
principle quantum number, n
angular quantum number, l
angular quantum number = azimuthal quantum number, l.
seen by radial distribution graph
what is the probability of finding an electron at distance r from nucleus in RDF proportional to
4 pi r squared psi squared
in rdf, is 1s max closer to nuc than 2s max
yes!!
meaning 1s shields 2s from nuc charge (not very well tho)
meaning 1s is a smaller orbital
in rdf how is 2s seen
m shape
smaller first hill
larger than 1s bc more further out
penetrates 1s orbital, e- are closer to nuc bc of this (although 2s dont rlly shield 1s)
1 radial node
what is the max in a rdf curve
the most probable area to find an electron
what is the value for psi at a radial node
0
means than e- are closer to the nuc
what is a core electron
electrons in a filled orbital
dont take part in chemical reactions
they shield valence electrons
low energy
close to nucleus
what is a valence electron
highest energy electron
they do chemsitry
get shielded by core electrons
order of orbital shielding strength
s
p
d
f
s shields best as it has a sphere shape.
what is shielding dependednt on in multi electron systems
principle quantum number
angular quantum number, l
shielding
electrons experience a lower nuclear charge (Zeff) due to e- closer to the nucleus repelling them.
depends on quantum number n.
larger n = larger shielding = lower Zeff
penetration
refers to the electron density of an electron around the nuc.
2s has more e- density near nuc than 2p so 2s is more penetrating
depends on principle and angular quantum number
electrons in orbitals haveee
different wavefunctions
therefore
different rdf
penetrating effect strength when n is the same
s
p
d
f
aufbau and why 2s is filled before 2p exp. rdf
2s penetrates 1s
meaning more e- density near nuc than 2p (and some of 1s)
mini max closer to nuc meaning lower in energy than 2p.
1s shields 2p more than 2s, 2s penetrates 2p and 1s, mini max closer to nuc, lower in energy
4s filled before 3d exp. rdf + aufbau
4s penetrates 3d
some 4s e- closer to nuc than 3d
filling 4s reduces shielding, 4s feels greater Zeff, lower in energy, more stable.
closer to nuc = lower energy = more stable
Zeffective = effective nuclear charge
Zeff = Z - S
what does the Zeff mean
the nuclear charge felt by a valence e- depends on what shell its on.
more shells between e- and nuc = more shielding = lower Zeff felt.
how does Zeff change from left to right
increases
e- are added but in the same shell as previous ones (esp bc d orbital can fit 10 e-!!) meaning they dont shield the nuc charge as well as if they were closer to the nuc.
what does the increase in Zeff across the period mean
increase in IE ( more energy needed to remove an electron )
decrease in atomic size ( nuc charge attracts e- more, stronger electrostatic forces of attraction)
what is S in Zeff = Z - S
slaters rules: shielding constant
- same shell / same n = 0.35
- shell below/ n-1 = 0.85
- 2 shells below / n-2 = 1
if theyre d or f everything shields it by 1.
how does Zeff change down a group
increases
what is ionisation enery
minimum energy needed to remove an e- from a mole of gaseous atoms (making sure both ion and e- have 0Ke after)
ionisation energies are always
positive +
energy is needed for this to happen
ionisation energy equation
E(g) –> E(g)+. + e-
why is the IE energy larger for the 2nd IE
removing an electron from a positively charged ion required more energy than removing it from a neutral one
what group has the highest IR
noble gases
which group has the smallest IR
alkali metals
trend of IE across a period
increase IE
due to increase Zeff
e- exp more nuc charge, holding e- stronger to nuc, needs more energy to be removed.
borons Ie is lower than Be
Be = 2s
B = 2s 2p
2s penetrates more, higher Zeff felt, held tighter to nuc, more energy needed to remove
2p = higher energy, easier to remove. larger l value.
O IE less than N
N = 2p3
O = 2p4
O e- is paired up, less energy needed to remove e- due to repulsion DAOIER
repuslion between 2 paired electrons
destabilising effect of interelectronic repulsion
exchange energy
number of parallel electron pairs.
more pairs = more stable
additional stability in half filled or completely filled shell.
3 e- = 3 parallel pairs.
trend of IE down a group
IE decreases
less energy needed to remove an e-
increase in n, not enough increase in Zeff
Ga has higher IE than Al even with a higher n ?
e- are added but to 4p orbital (after 3d10 orbital) .
d orbital shield weakly.
4p penetrates 3d bc s>p>d
Ga 4p1 electron exp larg Zeff than Al 3p1 as s>p>d shielding and bc 4p penetrate 3d.
p cant pen s. s can pen anything.
look at what can pen, look at what can shield
electron affinity
electron attachment energy
energy change when adding 1e- to a gasueous ion atom
opp of IE
+/- values
electron affinity equation
E(g) + e- –> E(g) -
group 17 electron affinity values
halogens
- XXX
NEGATIVE
no energy needed to add an e-.
they want the e-.
group 18 electron affinity values
noble gases
+ XXX
energy is needed to add an e-.
they dont rlly want an e-.
atom with largest electron affinity
Cl - chlorine
not F bc F is so small it repels the e-.
left to right electron affinity
increases (more negative)
until noble gases (group 18)
bc Zeffffffff
down a group electron affinity
decreases (more positive)
aka more energy needed to add an e- to it.
why do group 1 have - electron affinity values.
aka no energy is needed to give an e-
bc u add into s orbital
low in energy
penetrate close to nuc
high electrostatic attraction
why do group 2 have a + electron affinity value
aka energy is needed to give e-
bc u would be adding to the p orbital
higher in energy
higher l value.
energy of e- depend on n and l.
why do group 15 have lower electron affinities than group 14
its harder to add electrons to group 15 than 14
in group 15, adding an e- will cause pairing of electrons in the p orbital.
these e- pairs will experience the destabilising effect of interelectronic repulsions.
in group 14, adding e- does not cause them to pair, theres 1 e- in each p orbital.
why does the first period of p block have slightly lower electron affinities
their small size due to high Zeff causes the e- added to be repelled.
more energy is needed to add an e- to this row compared to the 2nd p block row.
lone pair lone pair repulsions.
relationship between IE and electron affinity
generally: easier to add = easier to take away
drop for O and F in EA due to their small size causing repulsion.
electronegativity
atoms ability in a molecule to attract a bonding pair of electrons in a covalent bond to itself.
pauling electronegativity
A-A and B-B -> A-B
if enthalpy of AB is higher than AA or BB. – ionic contribution, nonpolar to polar.
big electronegative difference between A and B
x of F is 4.0
muliken electronegativity
measure electronegativity based on IONISATION ENERGY and ELECTRON AFFINITY
scaled to match paulings scale.
alfred rochow electronegativity
measure electronegativity based on effective nuclear charge and covalent radius
scaled to match pauling
same electronegative atoms in a bond
bond is nonpolar
equal distribution of e- across the bond
both attract same amount of e-.
one atom more eelctronegative than other in a bond
bond is polarised
more electronegative atom attracts more e-.
degree of polarisation is proportional to electronegativity.
larger electronegative difference favours
making of ions
ionic bonding if they are more than 2 units different
more / less electronegative atoms are more likely to form
ionic bonds
atomic radii
difference between 2 nuclei
internuclear distance = bond length = affects a bonds energy
diff atomic radi occurs when
same atom but different bonds are made.
covalent
ionic
vdw
metallic
why is it impossible to find size of atom
only distance between nuc can be experimentally measured
probability of finding an e- far away from nuc is never 0. asympnotic wf or rdf??
even if distance from nuc was limited to x, radius of atom when measuring e- distance will change between different compounds.
covalent radii - single bonds
use experimentally measured bond lengths (nuc to nuc)
then divide by 2 to get atomic radius
half ther interatomic distance in a homonuclear diatomic.
half Br - Br bond length
known radii can be used to find unknown ones if known is bonded to unknown.
double and triple bonds are shorter than
single bonds
this must be remembered when caluclating atomic radi based on experimentally deduced single bond lengths.
covalent radi trend
across table: decrease
larger Zeff contracts orbital size
down group: increases in size
higher ‘n’ value.
how do Al and Ga have the same atomic radii
Zeff
Ga has e- in 4p but 3d shield weakly so 4p experiences strong Zeff.
4p also penetrate 3d
bc p>d
same contraction as Al
D BLOCK CONTRACTION
filling of 4f orbitals as u go from In to Ti (n 5 –> 6) causing similar atomic radii
LANTHANDIE CONTRACTION
metallic radii
one half of the internuclear distance in a metal
based on the atoms coordination number (its packing)
standardised to a 12 coordinate geometry
more neighbours = larger radius
van der waals radii
1 half the internuclear distance between 2 atoms that arent bonded in solid or liquid state (so atoms are in contact)
only known for some elements
values can vary considerably.
ionic radii
determined from crystal structures.
internuclear distance is the sum of anion + cation radii
we arent sure the precise distance of each. aka where the cation ends and where the anion starts.
anions radii are usually larger: less Zeff holding the extra e-.
in ionic radii, what happens as the charge becomes more positive
ionic radius decreases
less electrons
stronger nuc charge
holds atom closer together
what happens to ionic radii when the oxidation state increases
ionic radius decreases
charge of cation increases
