General main group

Question 1

Electron poor groups

Answer 1

Groups 1, 2, 12, 13

Question 2

Electron poor

Answer 2

Too few valence electrons to provide a pair for every bonded atom in a molecule
Lewis acidic (and highly electrophilic) metal centres
Multicentre covalent (or ionic) bonding

Question 3

What is multicentre bonding?

Answer 3

Multicentre bonding occurs in molecules where there are not enough electrons to allow at least one electron pair bond between each adjacent pair of atoms
Electron pairs occupy orbitals encompassing 3 or more atomic centres
e.g. diborane, B2H6

Question 4

Electron precise groups

Answer 4

Group 14

Question 5

Electron precise

Answer 5

An octet configuration at the metal centre leads to molecular compounds with diminished Lewis acidity (and electrophilicity)

Question 6

Electron rich groups

Answer 6

Groups 15, 16

Question 7

Electron rich

Answer 7

Metal centre leads to molecular compounds with diminished Lewis acidity (and electrophilicity)
Presence of lone pairs

Question 8

Polarity of M-C bond for main group organometallics

Answer 8

(Li) and rest of group 1, Ca, Sr, Ba = highly polar ionic bond, structures dominated by electrostatics
(Li), Be, Mg, Al, (Zn) = more polar covalent bond, structures often dominated by multicentre bonding, little or no M-M bonding
(Zn), rest of group 12 and groups 13-16 (from 3rd row down) = less polar covalent bond, structures often dominated by sigma-bonding, pi-bonding and M-M bonding also possible. Bonding dictated by orbital overlap

Question 9

Electronegativity difference for M-C (alkyl) bonds

Answer 9

Highest difference with group 1 metals

Difference decreases across the period

Question 10

Organometallic compounds of groups 1, 2 and 13

Answer 10

Uses of these compounds are generally a result of the reactivity of the M-C bond
React with water/protic reagents to eliminate alkanes (protonolysis)
e.g. R2Mg + R’OH —> RMgOR’ + RH
AlR3 + ROH —> (R2Al-OR)n + RH

Question 11

R2Mg + R’OH —> RMgOR’ + RH

Answer 11

Reaction driven forward by formation of MgO bond

Question 12

AlR3 + ROH —> (R2Al-OR)n + RH

Answer 12

Al-R bond is sufficiently basic enough to deprotonate water/alcohol

Question 13

Organometallic compounds of group 14

Answer 13

For group 14 elements, the electronegativity difference between M and C is much less
M-C bond is weakly polar but much less reactive
Most uses of group 14 organometallics rely on the stability of the M-C unit