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73 Cards in this Set

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Discuss Effective nuclear change?


-across period, add proton and electron, electrons not efficient at screening charge ∴Zeff increases across period


-estimate zeff with Slaters rules

Discuss Orbital energies?


-as number of protons increases orbital energy decreases


-2s is more penetrating than 2p with the energy gap increasing with increasing atomic number


Equation for orbital energy?

E = - Zeff²RH/n²
Discuss atomic radii?

-increase down a group, decrease across period


-Ga<Al due to transitinon metal contraction

Discuss Ionisation energy?


-decreases down a group, increases across a period


-Ga>Al -TM contraction


-Be>B - 2p higher energy than 2s


-N>O - exchange energy

Discuss electronegativity?


-increases across a period and decreases down a group


-Ga> Al, Si> Ge TM contraction

Discuss elements in top right corner?

small radii, High IE, Highe electron affinity, readily form anions
Discuss elements in bottom left corner?

Large radii, low IE's readily form cations
Discuss group 1 metals?


low 1st IE but very high 2nd IE


=> chemistry is dominated by tendency to lose a single s electron


=> less variation in chemistry than for elements of other main groups



∆χ =0-0.5

covalent non-polar

∆χ=0.5-1.8

covalent polar

∆χ>2.0

Ionic
Discuss group 1 halides?

for ∆Hf⁰:


-MX becomes less negative F->Cl->Br->I


-MX becomes more negative Li->Na->K->Rb->Cs


except for X = F which is the opposite due to small size of F⁻



Born Haber Cycle (constituents)?

fH⁰ = ∆vapH⁰ + ∆ionH⁰ + ½∆dissH⁰ + ∆EAH₀ -∆lattH⁰
Group 1 oxides and hydroxides?


react with water to give hydroxides or dioxygen to give oxides(O²⁻), peroxides(O₂²⁻) and superoxides (O₂⁻)


-Li gives oxides


-Na gives oxides and peroxides


-K gives peroxides and superoxides


-Rb and Cs gives superoxides

Group 1 hydrides?


rock salt structure (cube with each corner filled with an atom)


-strong bases


-ionic


-NaH is a common strong base, nuceophile, reducing agent



alkyl lithium?


small ∆χ ∴ covalent character


-polarised bond


-MeLi acts a nucleophile and base


-tetrameric (MeLi)₄


-4 centre 2 electron bond at each Li₃ face

How do we know if reaction is favourable from its ∆E?
∆G = -nFE⁰
Discuss group 2 alkaline earth metals?

-chemistry is dominated by formation of +2 ions


-all form M²⁺


-small size of Be²⁺ means covalent compounds dominate for this compound (and to a lesser extent magnesium)

polarising power?


the ability of an atom to polarise the electron density around a neighbouring atom



Polarisability?

the ability of an atom to be polarised by a neigbouring atom (how easily electron density around an atom is distorted)
Discuss group 2 halides?

-Chlorides, bromides and iodides of Mg, Ca, Sr and Ba are all ionic, water soluble salts


-conduct in the melt


-Fluorite structure is adopted by many MX² solids


BeCl₂:


-long polymer chain in solid state


-monomer or dimer in gas phase


-does not conduct electricity in the melt


-soluble in donor organic solvents



explain BeCl₂?

Be is Td ∴ sp³


Be-Cl-Be angle = 82 ∴ p orbitals (∼90)


-one normal 2 centre - 2e⁻ bond


-one dative 2 centre - 2e⁻ bond (lone pair on Cl)


-The Cl is bridging


-gives a polymeric structure


-BeCl₂ is a lewis acid therefore lewis bases will disrupt dative Cl-> Be bond and hence can be dissolved in donor organic solvents



Group 2 hydrides?


-Ca- Ra hydrides are ionic adopt distorted hcp structures and together with the Group 1 hydrides are the saline hydrides


-BeH₂ and to a lesser extent MgH₂ are covalent


-BeH₂ -linear gas phase H-Be-H, thermally stable polymeric structure in solid state


Reason BeH₂?

Be is Td ∴ Sp3


-Be-H-Be 3 centre 2e⁻ bonds


-electron deficient ∴ reacts with lewis bases and is less leactive to water

alkyl beryllium?


polymeric structure similar to BeH₂


-CH₃ is isolobal with H


-bulkier alkyls are dimeric or linear depending on steric congetstion


-3c 2e⁻ bond

Grignards?

RMgXs readily solvated by ether giving four coordinate Mg centres


-at high concentrations can condense into polymeric structures formed by displace ment of a solvent molecule by the lone pair on a halide

Group 2 carbonates?


BeCO₃ only exists under an atmosphere of CO₂


MgCO₃, CaCO₃ and SrCO₃ are stable but decompose with heat


BaCO₃ is stable to heat


-down group, M less electronegative, less polarising, decomposition requirers higher temperature


-Lattice enthaply is highest for small cation + small anion

Solubility of salts in water?

Discuss group 13?


-trend from covalent to ionic bonding down the group (form cations more readily down group)


-TM/lanthanide contraction explains deviations from expected trends in properties


-all elements adopt +3 oxidation states,


-+1 oxidation state becomes more prominent down the group (inert pair effect)

The alternation effect?

(transitionn metal/ d block/ lanthanide contraction) e.g. Al < Ga (sum of first three ionisation energies)


Ga has additional protons in nucleus, d electrons poorly shielded


=> strong attraction between nucleus and 4p¹ electron


=> increase in Ionisation energy


Ln -> Tl same but for 4f¹⁴ electrons are poorly shielded

inert pair effect?

e.g. Tl


6s orbitals low in energy and penetrating


ionisation energy not compensated by lattice enthalpy of e.g. TlCl₃ ∴ +1 oxidation state preferred

B₂H₆ structure and bonding?


B - sp³ hydridised


-4 Terminal 2 centre 2 electron bonds


-2 bridging 3 centre 2 electron bonds

Group 13 halides?


more covalent than group 2


-BX₃ displays significant π-bonding which is partly responsible for the planar structures due to its empty p orbital which can accept lone pairs

AlF₃?


ionic (∆χ=2.37)


forms infinite salt structure with octahedral coordinated metal ions

AlBr₃?


∆χ = 1.35 therefore molecular covalent


-exists in dimeric form with dative bonding from Br to empty Al orbitals similarly with AlI₃

AlCl₃?

ionic in the solid state but form dimers in the melt and in the gas phase ∆χ = 1.55 (border between ionic and covalent
Frustrated Lewis Pairs?


trivalent boron compounds are strong lewis acids


trivalent phosphines are lewis bases


-bulky groups attached to B and P hinder adduct formation giving a highly reactive species which can heteroyltically split H₂ giving a main group hydrogenation catalyst


-used to activate alkynes and CO₂



Group 14?

oxidation states of +4 and +2 common, with +2 becoming more prevalent down the group (inert pair effect)


+3 oxidation rare, found only in compounds with E-E or radical systems


-Chemistry dominated by covalent compounds

Group 14 bond hydrides?


-covalent bond enthalpy of hydrides decreases down the group, due to poorer orbital overlap


-Boiling point of hydrides increases down the group due to increased van der Waals

Group 14 halides and oxides?


-bond enthalpy decreased down group due to poorer overlap


-boiling point decreases down due to increased van der waals


-CX₄ compounds are lower than expected due to steric demand around small C


-Si often higher bond energies than expected due to d orbital interections



Bonding in silicon compounds?


-Si-F bond is the strongest single bond due to overlap between filled 2p orbital on f and empty 3d orbital on Si


-SiO₂ favours polymer network of Si-O single bonds compared with CO₂ because Si=O<2Si-O while C=O > 2C-O

Thermodynamic and kinetic stability of group 14?

-methane is thermodynamically unstable but it is kinetically inert


-SiH₄ is spontaneously flammable in air - kinetically labile


-same for halides in water


-CCl₄ is stable in water


-SiCl₄ reacts vigorously in water


H₂O struggles to attack C due to size of Cl groups



Carbenes?


CCl₂ exists but is quite reactive


-trigonal sp² hydridised


-can be singlet or triplet dependant upon groups attached (CCl₂ - singlet ground state, R₂C - triplet gound state) singlet leaves empty orbital for π donation into it


-Applications as ligands for transition metals in catalysis



Carbides?


-binary compound of cabon and a metal/metalloid


-saline carbides - group 1 and 2 (and Al)


-metallic carbides - transition metals


-metalloid carbides - boron and silicon

Saline Carbides?


Intercalation compounds


-Formed from graphite and metal vapour or metal dissolved in NH₃


-strong reducing agents


Dicarbides (acetylides)


-formed by reaction of metal and carbon at very high temperature


-Ionic structure with anion C₂²⁻


Methides


-Be₂C and Al₄C₃


-borderline between saline and metalloid


-directional bonding implies not purely ionic

Catentation?


formation of rings and chains by atoms of the same element


E-E bond energies decrease down group


-important for C and Si, less so for Ge and SN


(C₆₀, C₇₀, buckytubes etc)


(SiMe₂)n for n = 5-100


(GenH2n+2) for n = 1-10


SnnH2n+n for n = 1-6



Group 14 double bonds?


E=E bond strength decreases down the group due bigger atoms + more diffuse orbitals => longer bonds with poor overlap => weaker and more reactive


-Bulky R groups are required to favour double bonded molecules of the heavier group 14 elements

Group 15?


stable electronic configuration from reduction to -3 or oxidation up to +5


-lower down group +3 oxidation is most stable due to inert pair effect

allotropes?

different structural forms of the same element in which the chemical bonding is different
Group 15?

N -> non-metal


Bi-> characteristic properties of mani-group metal


oxidation = -3 up to +5


Bi +3 most stable due to inert pair effect

Allotropes of group 15?


N: N₂ most common, azide (N₃⁻) + few others


P: loads and loads of them


As, Sb, Bi: less than P

White phosphorus?


P₄ (triangular prism with p at each corner


-highly strained 60 bond angle


-highly reactive (spontaneously ignites in air, burns under water) giving phosphorous acid (H₃PO₃)in low oxygen, and phosphoric acid (H₃PO₄) in excess oxygen

Nitrogen oxides?

-variety of oxidation states,


-π-bonding due to efficient overlap of 2p orbitals
-use MO energy level diagrams to explain everything

Group 15 halides?


PX₃ are lewis bases (NCl₃, NI₃ are explosive)


-pentavalent halides for P, As, Sb, Bi not N due to size


-have to use MO theory to explain many properties as hybridisation is not very useful

Hypervalency?
possible for large elements due to size and access to D orbitals
Boron-Nitrogen compounds?


-Borazine (isolectornic with benzene) similar structures but different electronegativities give different reactivity


-Boron Nitride B-N-B-N-B


-graphite like compound


-diamond like compound


-borazane aka amino boranes

Nitrogen - Phosphorus compounds?

phosphazenes
Group 16?


oxidation states -2 to +6


-high electronegativity of O means +2 is max oxidation state



oxygen allotopes?

O₂ and ozone
Sulfur?


extensize allotropy


-all forms contain S-S single bonds like S₈ rings

Group 16 hydrides?


-Melting/boiling point increases with increasing size, H₂O exception


-E-H bond enthalpy decreases down group - poor orbital overlap


-H-E-H bond angle decreases due to less s-p mixing

Group 16 halides?


-Oxygen fluoride -rare example of positive oxygen oxidation state


-sulfur fluorides unstable towards hydrolysis with exception of SF₆


Group 16 polyanions and polycations?


polysulfides (Sn²⁻) for n = 2,3,4,6 depending on size of M in M₂Sn


S₈²⁺ Se₄²⁺ cyclic /bicyclic can be prepared

SxNx compounds?


tetrasulfur tetranitride


-extremely sensitive to explosive decomposition


-orange solid


-cradle shaped with weak bonding interactions between S atoms across the ring


poly(sulfur nitride)


-one-dimensional polymer


-coducting at room temperature, super-conductor at liquid He temperatures


-inert to hydrolysis,


-slowly decomposed by hydroxide

Group 17?


-oxidation states -1 to +7


-F always -1 and able to stabalize high oxidation states of other elements


-poorer overlap for increasing size of atoms (with more diffuse orbitals) down group, decreasing bond enthalpy, exception F which has a really low bond enthalpy

Group 17 hydrides?


stability decreases down the group due to increasing mismatch in atomic sizes


-HF is a volatile liquid wheras other HX are gases at RT


-HF is extremely toxic and corrosive, able to attack glass, metals, concrete and bone

Group 17 interhalogens?

XY, XY₃, XY₅ and XY₇
polyiodides?


I₃⁻ to I₉⁻ exist


-sensitive to the countanion


-bond length longer than in I₂

Hypervalent iodine compounds?

alternative to metal -based oxidising agents


-lower toxicity


-easier to handle


-milder reaction conditions







Group 18?

Xenon has developed covalent chemistry
Group 18 elements?


monoatomic gases


-He used as coolant


-Ne, Kr used in lighting


-Ar used as inert gas


-Xe propulsion of ion engines


-Rn radioactive so not investigated

Xenon?


fluorides of xenon


-XeF₂, XeF₄, XeF₆


-all reactive, highly oxidising


xenon oxides


-XeO₃


-explosize and highly oxidising