Main Group Chemistry

Front 1

Effective nuclear charge trend

Back 1

Increases L --> R
Not much change T --> B

Front 2

Covalent radius trend

Back 2

Decreases L --> R
Increases T --> B

Front 3

Ionisation energy trend

Back 3

Increases L --> R
Decreases T --> B

Front 4

Electronegativity trend

Back 4

Increases L --> R
Decreases T --> B

Front 5

Inert pair effect

Back 5

P-block elements often form compounds in which they are in an oxidation state 2 less than the group oxidation state. Increasing tendency for the s2 pair not to be used in bonding as you go down the group. Bond energies also fall - not enough to compensate for promoting an s electron to make it available for bonding.

Front 6

How does difference in electronegativity affect a bond strength?

Back 6

A greater difference in electronegativity between two elements will lead to a stronger bond between them

Front 7

How do multiple bonds change going down a group?

Back 7

Multiple bonds decrease in strength going down a group due to weakening pi bonds and poorer overlap

Front 8

Effect of size on coordination number

Back 8

Larger atoms can support higher coordination numbers

Front 9

Trends between groups 14-17

Back 9

One extra electron per atom going from 14 - 15, 15 - 16 etc.
Group 14 - 4 bonds
Group 15 - 3 bonds, 1 l.p.
Group 16 - 2 bonds, 2 l.p's
Group 17 - 1 bond, 3 l.p's

Front 10

How to rationalise compounds (4 points)

Back 10

i) Change in electronegativity
ii) Pi-bonding
iii) Element size
iv) Vacant orbitals

Front 11

Electronegative E - Is E-OH acidic or basic?

Back 11

E-OH --> EO- + H+
Acidic

Front 12

Electropositive E - Is E-OH acidic or basic?

Back 12

E-OH --> E+ + OH-
Basic

Front 13

VSEPR

Back 13

Front 14

Wade's Rules

Back 14

1) Count all valence electrons
2) Divide by 2 to get no. of pairs
3) Subtract 1 pair for each exohedral B-H
4) Remaining pairs are PSEP's
5) N+1 = Closo
N+2 = Nido
N+3 = Arachno
(n = number of vertices)

Front 15

Anomalies in periodicity

Back 15

Usually reflect presence of d or f rows which have poor shielding

Front 16

Borane reaction with base

Back 16

[BnHn]2-

Front 17

Boranes reaction with alkynes

Back 17

Carboranes e.g. C2B10H12

Front 18

Properties of silicones

Back 18

Thermal oxidative stability
Flexible due to low energy bending of bonds
Hydrophobic
Me groups can be substituted

Front 19

Formation of phosphazines

Back 19

[NH4]Cl + PCl5 + heat

Front 20

Bonding in phosphazines

Back 20

Electrons donated from N lone pair to vacant sigma* orbital on P

Front 21

Reaction of phosphazines with heat then nucleophile

Back 21

Polymer with Cl groups substituted for Nu

Front 22

Formation of S4N4 (and S8)

Back 22

[NH4]Cl + S2Cl2 + heat

Front 23

Reaction if S4N4 with heat and Ag

Back 23

S2N2 and (S=N) polymer

Front 24

Properties of (S=N) polymer

Back 24

Metallic conductor
Low temperature superconductor

Front 25

Formation of ammonia borane

Back 25

MeNH2 + BH3

Front 26

Effect if oxidation state on electronegativity

Back 26

Higher oxidation state --> more electronegative

Front 27

Heating ammonia borane

Back 27

100C (-H2) - cyclic boron nitride
200C (-H2) - n methyl borazine (cf benzene)
Further heating - hexagonal boron nitride (cf graphite)
Very high temp and pressure - cubic boron nitride (cf diamond)

Front 28

Formation of phosphazines

Back 28

[NH4]Cl + PCl5 + heat

Front 29

3 centre 2 electron bond

Back 29

3 atoms share 2 electrons
E.g. B-H-B - one electron from each boron shared over the three atoms including H+

Front 30

Why do 4p elements experience a greater effective nuclear charge?

Back 30

Presence of 3d electrons - poor shielding. So electrons are held more tightly than would be expected.

Front 31

Homonuclear bond energies

Back 31

Weak between electronegative atoms due to lone pair repulsion. Decrease down a group as orbitals get bigger and overlap becomes poorer.

Front 32

Heteronuclear bond energies

Back 32

2A-B > A-A + B-B
Change in electronegativity strengthens the bond

Front 33

Amphoterism

Back 33

Can act as both acidic and basic

Front 34

Structure of dihydrates

Back 34

Larger atoms can support a larger CN and disfavour double bonds - so octahedral with (OH)6 is preferred.
Smaller atoms prefer a H bonded adduct with double bonds to oxygen.

Front 35

Hydrolysis of xenon compounds

Back 35

Leads to oxides, oxoanions and oxyfluorides

Front 36

Affect of oxidation state on acidity

Back 36

Higher oxidation state - more acidic

Front 37

Oxidation of Xe2 to [Xe2]+

Back 37

Makes it more stable as bond order increases from 0 to 0.5. Electrons removed from antibonding orbital.