S/P-block

Question 1

How is the periodic table organised

Answer 1

1. Atomic number
2. Orbitals
3. Energy

Question 2

What are the trends in effective nuclear charge

Answer 2

Zeff increases across period
no. protons increases
not compensated for by e-

Zeff increases down group
no protons increases charge
not fully compensated for by e-

Question 3

What are the trends in atomic radius

Answer 3

Decrease across period
increasing Zeff

Increase down group
increasing n

Question 4

What are the anomalies in atomic radius

Answer 4

Li&raquo_space; H
effective screening by 1s orbital

Al ~ Ga
d-block contraction

Tl ~ In
f-block contraction

Question 5

What are the trends in first ionisation energy

Answer 5

Increasingly endothermic across period
increasing Zeff
no increase in n

Decreasingly endothermic down group
increase in n
∴ e- spends more time further from nucleus
∴ e- more weakly held

Question 6

What are the anomalies in first ionisation energy

Answer 6

Be -> B
e- in p-orbital has higher energy
∴ less tightly bound than s-orbital

N -> O
e- paired in O
∴ lower than expected energy

Question 7

What are the trends in e- gain energy

Answer 7

More exothermic across period
increase in Zeff
no increase in n

Less exothermic down group
decreasing Zeff

Question 8

What are the properties of non-metals

Answer 8

High IE
-ve electron gain energy
𝜒 > 2.2
Small radius
Good orbital overlap

∴ share e-
∴ covalently bonded

Question 9

What are the properties of metals

Answer 9

Low IE
𝜒 < 1.9
Large radius
Weak orbital overlap

∴ sea of e-
∴ metallic bonding

Question 10

What are the trends in bond strength of binary hydrides across a period

Answer 10

Mean bond enthalpy increases
Li -> F
increasing covalency
∵ increasing mean 𝜒
C -> F
increasing bond polarity
∵ increasing Δ𝜒

N doesn’t follow trend
∵ e- pair effect

Question 11

What is the equation for electron density

Answer 11

Ed(AB) = ( (Ed(AA) + Ed(BB))/2 ) + (𝜒A - 𝜒B)^2

Question 12

What is the trend in bond strength of binary hydrides down a group

Answer 12

Decreases down group
decreasing Δ𝜒
∴ reduced electrostatic contribution
increasing bond length
∵ reduced orbital overlap
increasing mismatch orbital energy

Question 13

What are the structures of group 1 & 2 hydrides

Answer 13

1 = predominantly ionic w/ CCP

2 = predominantly ionic w/ rutile

Question 14

What is the trend in MP/BP of binary hydrides

Answer 14

Van der Waal interactions increase across period

2nd row hydrides stronger
∵ polarisation leads to h-bonds

HF more polarised
∴ stronger dipole
∴ able to form fewer H-bonds

Question 15

What is the trend in acidity of binary hydrides

Answer 15

Increases across period
increasing Δ𝜒
∴ increasing polarisation

Increases down group
decreasing Δ𝜒
∴ decreasing bond strength

Question 16

Why does water have greater conductivity than ammonia

Answer 16

Greater bond polarisation
Higher pKa
Better stoichiometry

Question 17

What is the isotope effect

Answer 17

Heavier mass
affects vibrational modes
affects bond strength
∴ MP/BP & pKa higher

Question 18

Why does reactivity increase down group 1

Answer 18

Lower IE
∴ lower barrier to reaction

Weaker metalic bonding
∴ lower MP/BP

Lower MP & higher density
increases contact w/ water

Faster rate of reaction
∴ more heat generated
∴eventually explodes

Question 19

What is the comparison of group 1 & 2

Answer 19

2 has higher 1st IE
∵ increased Zeff

2 has higher MP & ΔatH
∵stronger metallic bonding
∵presence 2 delocalised e-

Question 20

What are the trends in ionic radius

Answer 20

Cations smaller than neutral
loss of e-
∴ higher Zeff on remaining e-
loss of outer shell

Cation size decrease across period
∵ increasing valency

Anions larger than neutral
gain e-
∴ smaller Zeff on e-

Size ions increases down group
e- in higher energy shell
∴ spend more time further from nucleus

Question 21

What is the lattice dislocation energy

Answer 21

When 1 mol ionic solid
converted to gaseous ions

Endothermic
+ve enthalpy

Question 22

What is the Gibbs energy of solution

Answer 22

Energy change
when 1 mol ionic solid
is dissolved in water
to give solution of infinite dilution

Question 23

What affects energy of hydration

Answer 23

Smaller ions
w/ higher charge multiplicities
have higher charge density

∴ interact more strongly
w/ water molecule
leading to higher energy of hydration

Question 24

How do hydrated salts form

Answer 24

Lone pair e- of H2O
coordinate strongly
to charge dense metal ions
form highly ordered inner coordination sphere

Question 25

What are the trends in Gibbs energy of solution

Answer 25

Salts w/ large anions solubility in water decreases down group 1 & 2 Salts w/ small anions solubility in water increases down group 1 & 2 Group 2 have higher lattice enthalpy compounds generally less soluble enthalpy hydration also higher

Question 26

What are the trends in oxidation state

Answer 26

Expansion of octet not possible so max at N +5 Max OS easier down group ∵ IE & 𝜒 decrease Period 4/5 often favour lower OS ∵ inert pair effect

Question 27

What is the inert pair effect

Answer 27

Promoting e- from 2s -> 2p allows extra bond to form Gap from 4s -> 6s increases ∵ d/f-contraction Promotion E increases slightly down group ∵ relativistic effects & d/f-contraction Bond H decreases down group so E released from forming new bonds decreases ∴ payback to cost of promotion lower

Question 28

What are the relativistic effects

Answer 28

Velocity e- in heavier elements approaches appreciable fraction of c ∴ higher nuclear charge Leads to increased mass e- & contraction of orbitals Leads to higher promotion energies

Question 29

What are the trends in σ-bonds

Answer 29

Repulsion between e- lone pairs weakens σ-bonds Decrease down group ∵ increasing atomic radius & reduced orbital overlap

Question 30

What are the trends in bond enthalpies

Answer 30

Increase across period ∵ increasing 𝜒 lone pair repulsion weakens bonding for N2, O2 & F2 Decrease down group as nuclear radii increases & orbitals become more diffuse ∴ overlap weaker

Question 31

What are the trends in covalency in p-block

Answer 31

Bond enthalpy decreases down group ∵ larger more diffuse orbitals A-F enthalpies > A-Cl ∵ better orbital overlap & greater difference in 𝜒 ∴ Stronger polar covalent bonds for F 2nd row F bonds weak ∵ short inter atomic distances ∴ repulsion between lone pairs

Question 32

What are the trends in π-bonding

Answer 32

Orbital size increases down group σ-bond length increases ∴ rapid drop-off in overlap between perpendicular orbitals For Si 2σ-bonds strongly favoured Double/triple bonds only seen when stabilised by bulky groups to prevent rearrangement

Question 33

What is the bonding in O/N

Answer 33

Single bonds particularly weak ∵ repulsion between lone pairs Multi bonds energetically favoured

Question 34

What are the allotropes of P

Answer 34

Common allotropes form 3 σ-bonds Reactivity decreases from white -> black ∵ reduced strain Solubility/volatility decreases ∵ formation increasingly extended structures

Question 35

What are the trends in IE for group 13

Answer 35

IE increases w/ every e- lost ∵ increasing Zeff 1st IE lower as higher E p-orbital IE generally decreases down group but alternating effect due to d/f-contraction

Question 36

What are the trends in p-block oxides

Answer 36

Average 𝜒 increases across row ∵ difference in 𝜒 decreases ∴ increasingly covalent bonding

Question 37

What is back bonding

Answer 37

Back donation of e- from filled orbital of attached ligand to empty orbital of central atom Gives rise to pπ-pπ bonding

Question 38

What is the effect of lewis acid/bases on back bonding

Answer 38

Addition of lewis acid distorts shape & disrupts pπ-pπ bonding

Question 39

What are the trends in bonding of group 18 B halides

Answer 39

Lewis acidity increases down group 17 BF3 < BCl3 < BBr3 < BI3 ∵ weaker back bonding ∵ orbital size & energy mismatch

Question 40

What are the trends in noble gases

Answer 40

e- gain energy generally increases across period group 18 have full shell so unfavourable 1st IE Ar similar to O

Question 41

How do high oxidation states become easier to achieve in hypervalent halogens

Answer 41

As size central atom increases down group & 𝜒/IE decrease As size peripheral atom decreases & becomes more 𝜒 F particularly good due to weak F-F bonds

Question 42

What are the forms of P pentahalides

Answer 42

PF5 stable PCl5 exists as gas disproportionates in solid state to form PCl4 cation & PCl6 anions Br/I do the same form P4 cation & I- ∵ larger size

Question 43

What are the trends in bond angle

Answer 43

For AH3 decreases down group 15 size A allows H - A - H to be squashed more by lone pairs For AX3 Increases down halides ∵ reduced 𝜒 of bonding pair