Chemistry Of The S And P Block

Front 1

Discuss Effective nuclear change?

Back 1

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

-estimate zeff with Slaters rules

Front 2

Discuss Orbital energies?

Back 2

-as number of protons increases orbital energy decreases

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

Front 3

Equation for orbital energy?

Back 3

E = - Zeff²RH/n²

Front 4

Discuss atomic radii?

Back 4

-increase down a group, decrease across period

-Ga<Al due to transitinon metal contraction

Front 5

Discuss Ionisation energy?

Back 5

-decreases down a group, increases across a period

-Ga>Al -TM contraction

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

-N>O - exchange energy

Front 6

Discuss electronegativity?

Back 6

-increases across a period and decreases down a group

-Ga> Al, Si> Ge TM contraction

Front 7

Discuss elements in top right corner?

Back 7

small radii, High IE, Highe electron affinity, readily form anions

Front 8

Discuss elements in bottom left corner?

Back 8

Large radii, low IE's readily form cations

Front 9

Discuss group 1 metals?

Back 9

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

Front 10

∆χ =0-0.5

Back 10

covalent non-polar

Front 11

∆χ=0.5-1.8

Back 11

covalent polar

Front 12

∆χ>2.0

Back 12

Ionic

Front 13

Discuss group 1 halides?

Back 13

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⁻

Front 14

Born Haber Cycle (constituents)?

Back 14

∆fH⁰ = ∆vapH⁰ + ∆ionH⁰ + ½∆dissH⁰ + ∆EAH₀ -∆lattH⁰

Front 15

Group 1 oxides and hydroxides?

Back 15

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

Front 16

Group 1 hydrides?

Back 16

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

-strong bases

-ionic

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

Front 17

alkyl lithium?

Back 17

small ∆χ ∴ covalent character

-polarised bond

-MeLi acts a nucleophile and base

-tetrameric (MeLi)₄

-4 centre 2 electron bond at each Li₃ face

Front 18

How do we know if reaction is favourable from its ∆E?

Back 18

∆G = -nFE⁰

Front 19

Discuss group 2 alkaline earth metals?

Back 19

-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)

Front 20

polarising power?

Back 20

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

Front 21

Polarisability?

Back 21

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

Front 22

Discuss group 2 halides?

Back 22

-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

Front 23

explain BeCl₂?

Back 23

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

Front 24

Group 2 hydrides?

Back 24

-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

Front 25

Reason BeH₂?

Back 25

Be is Td ∴ Sp3

-Be-H-Be 3 centre 2e⁻ bonds

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

Front 26

alkyl beryllium?

Back 26

polymeric structure similar to BeH₂

-CH₃ is isolobal with H

-bulkier alkyls are dimeric or linear depending on steric congetstion

-3c 2e⁻ bond

Front 27

Grignards?

Back 27

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

Front 28

Group 2 carbonates?

Back 28

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

Front 29

Solubility of salts in water?

Back 29

Front 30

Discuss group 13?

Back 30

-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)

Front 31

The alternation effect?

Back 31

(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

Front 32

inert pair effect?

Back 32

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

Front 33

B₂H₆ structure and bonding?

Back 33

B - sp³ hydridised

-4 Terminal 2 centre 2 electron bonds

-2 bridging 3 centre 2 electron bonds

Front 34

Group 13 halides?

Back 34

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

Front 35

AlF₃?

Back 35

ionic (∆χ=2.37)

forms infinite salt structure with octahedral coordinated metal ions

Front 36

AlBr₃?

Back 36

∆χ = 1.35 therefore molecular covalent

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

Front 37

AlCl₃?

Back 37

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

Front 38

Frustrated Lewis Pairs?

Back 38

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

Front 39

Group 14?

Back 39

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

Front 40

Group 14 bond hydrides?

Back 40

-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

Front 41

Group 14 halides and oxides?

Back 41

-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

Front 42

Bonding in silicon compounds?

Back 42

-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

Front 43

Thermodynamic and kinetic stability of group 14?

Back 43

-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

Front 44

Carbenes?

Back 44

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

Front 45

Carbides?

Back 45

-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

Front 46

Saline Carbides?

Back 46

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

Front 47

Catentation?

Back 47

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

Front 48

Group 14 double bonds?

Back 48

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

Front 49

Group 15?

Back 49

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

Front 50

allotropes?

Back 50

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

Front 51

Group 15?

Back 51

N -> non-metal

Bi-> characteristic properties of mani-group metal

oxidation = -3 up to +5

Bi +3 most stable due to inert pair effect

Front 52

Allotropes of group 15?

Back 52

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

P: loads and loads of them

As, Sb, Bi: less than P

Front 53

White phosphorus?

Back 53

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

Front 54

Nitrogen oxides?

Back 54

-variety of oxidation states,

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

Front 55

Group 15 halides?

Back 55

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

Front 56

Hypervalency?

Back 56

possible for large elements due to size and access to D orbitals

Front 57

Boron-Nitrogen compounds?

Back 57

-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

Front 58

Nitrogen - Phosphorus compounds?

Back 58

phosphazenes

Front 59

Group 16?

Back 59

oxidation states -2 to +6

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

Front 60

oxygen allotopes?

Back 60

O₂ and ozone

Front 61

Sulfur?

Back 61

extensize allotropy

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

Front 62

Group 16 hydrides?

Back 62

-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

Front 63

Group 16 halides?

Back 63

-Oxygen fluoride -rare example of positive oxygen oxidation state

-sulfur fluorides unstable towards hydrolysis with exception of SF₆

Front 64

Group 16 polyanions and polycations?

Back 64

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

S₈²⁺ Se₄²⁺ cyclic /bicyclic can be prepared

Front 65

SxNx compounds?

Back 65

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

Front 66

Group 17?

Back 66

-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

Front 67

Group 17 hydrides?

Back 67

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

Front 68

Group 17 interhalogens?

Back 68

XY, XY₃, XY₅ and XY₇

Front 69

polyiodides?

Back 69

I₃⁻ to I₉⁻ exist

-sensitive to the countanion

-bond length longer than in I₂

Front 70

Hypervalent iodine compounds?

Back 70

alternative to metal -based oxidising agents

-lower toxicity

-easier to handle

-milder reaction conditions

Front 71

Group 18?

Back 71

Xenon has developed covalent chemistry

Front 72

Group 18 elements?

Back 72

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

Front 73

Xenon?

Back 73

fluorides of xenon

-XeF₂, XeF₄, XeF₆

-all reactive, highly oxidising

xenon oxides

-XeO₃

-explosize and highly oxidising