P-block Flashcards
How long must an element exist to be considered discovered
10 femtoseconds aka 10^-14s
Ionisation energy definition
The energy required to remove completely an electron from the gaseous atom or molecule in its ‘ground state’
Electron affinity def
The energy released when a gaseous atom, molecule or ion in its ‘ground state’ gains an electron
Electronegativity (χ) def
The ability of an atom to attract electron density towards itself in a molecule
What happens to bond strength if covalent + polar
Increased electrostatic/Coulombic attraction -> higher than expected bond strength
Highest electronegativity out of sp or sp3
sp as it has more s character so electrons held more tightly
Axes on Ketelaars triangle
Ionicity parameter: Difference in elec - (y ax). Covalency parameter: Average elec of 2 atoms
For an electron in p or s, how much do other electrons contribute to shielding according to Slater’s rules
Same ns, np, nd: 0.35 per e-. (n-1): 0.85 per e-. (n-2) or lower: s=1 (cancels out proton charge)
For an electron in d or f, how much do other electrons contribute to shielding according to Slater’s rules
If its also nd or nf: 0.35 per e. Anything else: s=1
In slaters rules: What if considering a 3d e-, are the 4s e- taken into account for sheilding?
No, higher groups are not considered
What is most electronegative out of sp and sp3
sp
What do Slater’s rules not take into account
Distance from nucleus or penetration
What is an alternative to work out effective nuclear charge other than slaters rules + its problem
Clementi-Raimondi explanation but all values for each orbital in atom must be looked up individually
How does radii vary with coordination number
More ligands means more e- density on metal -> increases apparent size
What happens to s-p separation down a group
It decreases bc they are further form the nucleus so s is not drastically more stable anymore
Why is the s-p separation in Ga and Ge higher than expected
10 extra protons from d block but f block not very shielding. Higher effective nuclear charge pulling in electrons -> more stabilised
What happens to s and p energies across a period
They decrease but s decreases more bc it is closer to nucleus (called better penetration)
Why does sigma and pi levels swap from N2 to O2?
S-p mixing: The gap between s and p gets too big for sp-mixing in oxygen so sigma becomes the lowest level
Trend of promotion energies down a group. Also what happens to other electrons that do not get promoted?
Increases w d-block exception for Ga + Ge. More energy required to promote e- from s to p. They have less electrostatic repulsion.
What is the ‘Inert Pair’ effect
The tendency of electrons in the outermost atomic s orbital to remain unionised or
unshared in compounds of the Group 13-16 elements.
OR
The observation that as a group is descended, the n-2 oxidation state becomes more
favoured (where n = group oxidation state)
Aka group 13 gets 3-2 = +1 oxidation state
One reason for inert pair effect
Covalent bond strength decreases down group bc poor orbital overlap. Therefore, bond enthalpy not enough for rehybridisation energy cost
Why is PbH4 not favourable but CH4 is
CH bonds are strong + promotion energy low -> promotes electron then hybridises (sp3) easier than weak Pb-H bonds + high promotion energy
What is the relativistic effect
Objects near speed of light gain mass. The heavier the element, the faster outer electrons go.
What is the theory of special relativity equatioin
m = m0 / sqrt (1 - (v/c)^2 ) where m0 = electron rest mass
What is it called when an e- gains mass from high speed which contracts orbital
Direct relativistic orbital contraction
Why is an orbital contracted when e- gains mass from speed
The e- can’t travel as far - smaller orbital
What happens to s, p, d and f during direct relativistic orbital contraction
S gets smaller. P contract but not as much (poorer penetration). d & f experience indirect relativistic orbital expansion since they are destabilised. Poorer penetration + higher shielding from s + p so expand
How is relativistic effect related to inert pair effect
S-electrons of heavy elements are more stable therefore less likely to be ionised/involved in hybridisation!
Why does bond strength decrease down group
Larger valence orbital volume but max 2 e- so more diffuse orbitals with lower charge density down group. Less orbital overlap so sharing of e- density is less effective
Why are single bonds favoured down groups
Larger covalent radius gives poor p (pi) overlap
Reason for difference in shape between NMe3 and N(SiH3)3
Si has empty d orbital which makes it flat, N doesn’t so pyramidal
What does valence mean
Number of e- the atom uses to form covalent bonds
Why are group 13 lewis acids
3 valence electrons means only have a valence of 3. Gives 6 valence e- total therefore electron deficient so a lewis acid
How can an atom have 4 bonds but a valence of 3
If it is a dative bond onto that atom
Why are N, O and F exceptions in homonuclear bond energy trend
Strong bonding interaction bc small orbitals BUT lower than expected because greater electrostatic repulsion bc lone pairs
Why is C-F weaker than B-F bond
C has a higher electronegativity than B. Also, C has full octet so cant accept pi donation bc not electron deficient
What are homonuclear bonds
Same element bonds eg F-F
Disproportionation of M = Al, Ga
3MX -> 3M + MX3
Use of Boron
Plant growth, Borosilicate glass, NaBH4, cancer treatment, borax = detergent + insectecide
Which boron halide is the strongest lewis acid
BI3 because largest p-orbitals gives ineffective sharing of pi-density. B is most e- deficient. Overtakes electronegativity trend
What happens to Al->Tl halides (not flourine)
Dimerisation bc poor orbital overlap
BX3 + ROH reaction
BX2(OR) + HX, can keep reacting to form B(OR)3.
Except BF3 as B-F bonds are strong
Stability of acid base complex (L) for flourides of Al, Ga, In
MF3L more stable than MI3L because no pi bonding so only electronegativity. F most EN so M most e- deficient therefore strongest Lewis acid. Also longer bonds
Name of boron hydrides
Boranes
What happens to boranes
Forms a B2H6 dimer with 3-centre 2-electron bonds. Use MOs to explain
What happens if B2H6 dimer is heated
Forms diff types of borane cluster
Maker G3 hydride more stable
In a dimer, have R groups with inductive effect -> less e- deficient -> more stable
What are Wade’s rules (7)
1) BH unit donates 2e-. 2) H donates 1. 3) 2- charge on atom = 2e-. 4) Sum of e- is 2n. n is PSEPs involved in cluser bonding. 5) n pair PSEPs gives polyhedron w 1-n vertices. 6) BH units = vertices: Closo. One less: Nido. 2 less: Arachno. 7) Place remaining H as terminal H atoms around open face (atoms with lowest coord number) and bridging
What is a PSEP
Polyhedral skeletal electron pair
Wades rules for carboranes
BH is isolobal to CH+ so must put negative charge on overall molecule when looking at units
Where should the cabon be placed in carboranes
The furthest apart = most thermodynamically stable
What is a carborane
Cluster of boron, carbon and hydrogen
What is special about Pb(IV)
It is an oxidising agent as it wants to reduce to PB(II) bc inert pair effect
Names of Si, Ge, Sn, Pb Hydrides
Silane, germane, stannane, plumbane (unstable)
Stability of group 14 halides and hydrolysis reaction
CX4 is hydrollytically stable. The rest: SiCl4 + 2H2O -> SiO2 + 4HCl
Why do group 14 halides become susceptible to hydrolysis down group
Greater electronegativity difference means stronger bond BUT larger atoms means less sterically hindered so more suscpetible to nucleophilic attack
Difference in group 4 halides MX4 and MX2
MX2 is more metallic bonding
Reaction of G14 halides + alcohols
SiCl4 + 4ROH -> Si(OR)4 + 4HCl
What are siloxanes/silicones?
Polymer with Si-O-Si.. backbone and Si atom carries 2 organic groups such as methyl/phenyl
First step in making silicones
Hydrolysis of silylhalides to make silanol.
Me3SiCl + H2O -> Me3SiOH + HCl
How do you make the shorts siloxane ever
Condensation of Me3SiOH — (-H2O)–> Me3Si-O-SiMe3
how are polymeric siloxanes produced from silanols
3 monomer units needed.
Terminal group: Me3SiOh —(-H2O)–> Me3Si-O–
Chain forming group: Me2Si(OH)2 -> –O-SiMe2-O-
Cross linking: MeSi(OH)3 -> Me-Si-(O-)3 up and down
What will react with silicones even tho its inert
Flourinating agents because Si-F bonds very strong
Why is Si-O stronger than C-O
p-pi - d-pi bonding. Filled 2p of O donates into empty 3d of Si
Whats is an organosilane
Has C-Si bonds
Why is tetramethylsilane (TMS) more stable than SiCl4
Sterically shielded, less polar bonds, Cl- better leaving group than Me-
What is oligomerisation
Converting monomerts to mactromolecuels with a finite degree of polymerisation
How can heavy group 14s be forced to make double bonds between each other AKA blocking oligomerisation
R2Si=SiR2 where R is a large sterically hindering group. With very large ones, can do RSi=–SiR (triple bond)
How are double bonds formed with SNR2
“Paw-paw” donor-acceptor bonding. One LP from sp2 orbital overlaps with empty p orbital at an angle on both sides.
What are G14 Zintl ions/phase. Example for Pb + colour changes
Clusters of G14. Pb(s) — Na, NH3—> 4Na+ + [PB9]-4. Blue solution to green when Pb dissolved. Na used bc very good reducing agent. Cryptand liagands enables crystallisation of Pb5 to come out. = The combo of cryptand with Na inside + Pb5 = zintl phase
What is a Zintl phase
They contain a Group 1 or Group 2 metal (as reducing agent), along with post-transition metals (Group 12) or the metalloids from Groups 13, 14, 15, or 16.
What is catenation
Same element bonding to each other to create chains/rings
Why is there little catenation of nitrogen
N-N single bond is weak bc despite efficient sharing of e- density -> e- rich so repulsion
How is N3- ion formed
6Li + N2 -> 2Li3N(s) because lattice energy is high
Colours of phophorous
Black, White (P4) and red
Poryphoric reaction of white phosphorus + use
Meaning: ignites in contact with air. P4 + 5O2 -> P4O10(s). Incendiary weapons, smoke grenades
Why is there not negative oxi state for N in N oxides
Oxygen is more electronegative so will have the -ve oxi state
2 structures of nitrogen oxide that has N in +4 oxi state
NO2. (brown) which turns to N2O4 (colourless) with gentle heating
Name of hydrides of N, P, As, Sb
Ammonia, phosphine, arsine, stibine
Difference between NH3 and PH3 bonds. What does it do to basicity
NH3 is sp3 hybridised. PH3 bonds through unhybridised p bonds (n) -> sigma (H). The lone pair on P is in the s orbital (sigma bonding). Relativistic effect: s also less likely to be hybridised. They are not basic bc LP not available.
Why does NH3 have relatively high BP?
High polarity and H bonding
How to make phosphine (PH3)
4H3PO3 -> PH3 + 3H3PO4 P in +5 oxi state is the driving force as it’s the most stable state
WHat is the Tolman cone angle
Measurement of M-P-R3 where M is top of cone and measurement is the lines connecting outer atoms of R to M then down to R again
What does a high tolman cone angle mean
Large R groups, sterically hindered
Which G15 form MX3 and MX5 halides
All form MX3. MX5 formed easiest with small halide and small group 15. Nothing w larger atoms than PBr5 forms it.
Bond angle in NH3 vs NF3
Smaller with NF3 because e- density is pulled away from N -> less electrostatic replusion between bond pairs
What happens to Ni(CO)4 as it reacts with PF3
CO is displaced by PF3 becasue it pulls more e- density from P making it a stronger pi acceptor. Therefore it has a stronger interaction with Ni, the metal
What happens to Pcl5 as it cools down
Forms lattice of [PCl4]+ and [PCl6]-
Group 14 super acids example
AsF5 or SbF5 + 2HF -> [H2F]+[SbF6]-. Really good source of protons
What are Paulings oxyacids rules
OmE(OH)m
pKa = 8-5m
pKa increases by 5 for every H lost
How can oxyacids of phosphorous polymerise
Chains or rings via P-O-P or P-P
Why does each successive ionisation become less favourable for P oxyacids
The negative charge from losing a H can be stabilised in resonance structure by putting double bond up on O
Name of group 16
Chalcogens
Oxyacids are prepared by hydrolysis from G16 di- and trioxides. Names of resulting acids?
SO2, SeO2…: -ous acids. (sulfurous acid,)
SO2 + H2O -> H2SO3
SO3…: -ic acids (sulfuric acid)
SO3 + H”O -> H2SO4
Names of 4 diff oxyacids of halides
HOX: hypohalous (hypochlorous acid) but generally unstable
HOXO: halous (chlorous)
HOXO2: halic (chloric acid)
HOXO3: perhalic (perchloric acid)
Chlorous acid ion
Chloric
Perchloric
Chlorite
Chlorate
Perchlorate
Why does ozone form back into O2
Highly exothermic reaction
3 common things about G16
Dissolve in oxidising agents, attacked by halogens, high oxygen-xontent molecs in fertilisers
Why are there a lot of allotropes of S
S-S catenation. Also bond distance + angles can vary greatly . Cycles are thermodynamically favoured
OH2 vs TeH2 bonding
OH2: sp3 hybrid. TeH2: p orbs at 90 degrees. One LP in remaining p orb and one in s orb
Why is SF6 very inert when SF4 and SeF6 is reactive
Se bigger size. It is no logner sterically hindered. MOre accessible to nucleophilic attack. Not due to thermodynamics, just kinetic as they can’t get to S in SF6
How does catenation happen for iodine
Not covalent bonds, only electrostatic interactions
Boiling point trend down G17
Increases. More electrons increasing the London dispersion forces. Has no permanent dipole
Why are F2 reactions violent
Small atoms causes short bond = high electrostatic repulsions. Element-F has high bond energy due to large ionic contribution from electronegativity
Production of hydrogen halides reactivity down group
Decreases as bond in product becomes weaker so reduced thermodynamic driving force for reaction
What happens if a HF reaction is done in normal glass
Si-F are stronger so HF will react with the glass
Draw Cl2O……. all oxi states lewis structures
Answer on 2nd page in note book
Halide oxyanions are axodising/reducing agents
Oxidising becasue don’t want to be +ve oxi state
XeF6 structure
Octahedron with 1 LP projecting out of 1 face. LP distorts octahedron by pushing 3 of ligands baking up faceb
What happens to XeF6 in solution and in solid
Solution: Becomes Xe4F24. Positions exchange in cogwheel mechanism so all atoms are equivalent. Solid: [XeF5]+ and F- in salt structure
Group 14: when are triplet vs signlet ground state
Carbenes = triplet where one electron is in sp2 and one in p. For rest: both e- in sp2 because more s character. However, if R groups are electropositive then E gets more e- so triplet state is more stable
What is borazine
Isoelec and structural to benzene. N donates LP to B. All N are +ve and B are -ve. Is aromatic
