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L1 exams > S/P-block > Flashcards

S/P-block Flashcards

1
Q

How is the periodic table organised

A
  1. Atomic number
  2. Orbitals
  3. Energy
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2
Q

What are the trends in effective nuclear charge

A

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-

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3
Q

What are the trends in atomic radius

A

Decrease across period
increasing Zeff

Increase down group
increasing n

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4
Q

What are the anomalies in atomic radius

A

Li&raquo_space; H
effective screening by 1s orbital

Al ~ Ga
d-block contraction

Tl ~ In
f-block contraction

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5
Q

What are the trends in first ionisation energy

A

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

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6
Q

What are the anomalies in first ionisation energy

A

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

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7
Q

What are the trends in e- gain energy

A

More exothermic across period
increase in Zeff
no increase in n

Less exothermic down group
decreasing Zeff

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8
Q

What are the properties of non-metals

A

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

∴ share e-
∴ covalently bonded

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9
Q

What are the properties of metals

A

Low IE
𝜒 < 1.9
Large radius
Weak orbital overlap

∴ sea of e-
∴ metallic bonding

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10
Q

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

A

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

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11
Q

What is the equation for electron density

A

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

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12
Q

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

A

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

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13
Q

What are the structures of group 1 & 2 hydrides

A

1 = predominantly ionic w/ CCP

2 = predominantly ionic w/ rutile

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14
Q

What is the trend in MP/BP of binary hydrides

A

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

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15
Q

What is the trend in acidity of binary hydrides

A

Increases across period
increasing Δ𝜒
∴ increasing polarisation

Increases down group
decreasing Δ𝜒
∴ decreasing bond strength

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16
Q

Why does water have greater conductivity than ammonia

A

Greater bond polarisation
Higher pKa
Better stoichiometry

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17
Q

What is the isotope effect

A

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

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18
Q

Why does reactivity increase down group 1

A

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

19
Q

What is the comparison of group 1 & 2

A

2 has higher 1st IE
∵ increased Zeff

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

20
Q

What are the trends in ionic radius

A

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

21
Q

What is the lattice dislocation energy

A

When 1 mol ionic solid
converted to gaseous ions

Endothermic
+ve enthalpy

22
Q

What is the Gibbs energy of solution

A

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

23
Q

What affects energy of hydration

A

Smaller ions
w/ higher charge multiplicities
have higher charge density

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

24
Q

How do hydrated salts form

A

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

25
Q

What are the trends in Gibbs energy of solution

A

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

26
Q

What are the trends in oxidation state

A

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

27
Q

What is the inert pair effect

A

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

28
Q

What are the relativistic effects

A

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

29
Q

What are the trends in σ-bonds

A

Repulsion between e- lone pairs
weakens σ-bonds

Decrease down group
∵ increasing atomic radius
& reduced orbital overlap

30
Q

What are the trends in bond enthalpies

A

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

31
Q

What are the trends in covalency in p-block

A

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

32
Q

What are the trends in π-bonding

A

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

33
Q

What is the bonding in O/N

A

Single bonds particularly weak
∵ repulsion between lone pairs

Multi bonds energetically favoured

34
Q

What are the allotropes of P

A

Common allotropes form 3 σ-bonds

Reactivity decreases from white -> black
∵ reduced strain

Solubility/volatility decreases
∵ formation increasingly extended structures

35
Q

What are the trends in IE for group 13

A

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

36
Q

What are the trends in p-block oxides

A

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

37
Q

What is back bonding

A

Back donation of e-
from filled orbital of attached ligand
to empty orbital of central atom

Gives rise to pπ-pπ bonding

38
Q

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

A

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

39
Q

What are the trends in bonding of group 18 B halides

A

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

40
Q

What are the trends in noble gases

A

e- gain energy generally increases across period
group 18 have full shell so unfavourable

1st IE Ar similar to O

41
Q

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

A

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

42
Q

What are the forms of P pentahalides

A

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

43
Q

What are the trends in bond angle

A

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

L1 exams (7 decks)

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