GROUP 13. (ns np ) 2 1
Metallic character decreases moving right, and we find that boron (B) is not a metal =
“metalloid”. B O i2 a3idic (cf. Li O is basi2, gives OH in water). Down group, metallic
character increases remainder are metals but oxides of Al and Ga are amphoteric (see below),
while those of In and Tl are basic.
B: B O (s) + 6 NaOH (aq) → 2 Na BO (aq) + 3 H O (l)
2 3 3 3 2
acid base salt water
(cf. HCl (g) + NaOH (aq) → NaCl (aq) + H O(l) ) 2
in water, forms B(OH) (or H 3O ), kn3wn a3 boric acid.
B(OH) + 2 H O ⇌ B(OH) + H O pK = 9.25
3 2 4 3 a
Al, Ga: oxides react with bases as above, but also with acids. They are “amphoteric” (= can
behave as both acids or bases)
Al 2 3s) + 6 NaOH → 2 Na AlO (aq) 3 3 H3O (l) 2
acid base salt water
A2 O3 (s) + 3 H S2 (4) → Al (SO )2 (s)4 33 H O (l) 2
base acid salt water
In, Tl: oxides are basic and react only with acids.
In 2 3s) + 3 H SO 2(l) 4→ In (SO ) 2s) +4 3H O (l) 2
base acid salt water
Bonding: B compounds are covalent, Al are sometimes ionic and sometimes covalent; ionic
character increases down the group.
All form +3, but Tl also +1. In general, when two oxidation states are possible, lower one
becomes more important down the group, and its properties are more metallike.
1 Again, B (period 2) more different from the rest of group. For example, B forms many electron
deficient compounds: stable but nevertheless reactive to Lewis bases ⇨ attain an octet
e.g., B3 :F: B has only 6 e in its outer (valence)
:F:B:F: shell ∴ strong Lewis acid∴ will accept
electron pair from Lewis base
e.g., 3F + 3:NH 3 F B─N3
this is source of acidity of 3B(OH2 + H O → 4B(OH) + H
Uses: Plentiful. 2 3 used in production of borosilicate glass. 3(OH) (boric acid) used as
disinfectant, eyewash, insecticide2 4a5[B O 4OH) 2⋅8H O used in washing powders.
Boron hydrides BxHy very important class of compounds.
Aluminum sulfate used in water purification, dye industry, antiperspirants, etc.
Al O used as a support for industrial catalysts, chromatography supports, etc.
BN compounds similar to analogous C compounds. e.g.
borazene like benzene.
Borazon (BN) ∞has a similar structure to diamond and
thus also very hard.
Be with Al (and B with Si)
Be and Al have similar properties
e.g., similar covalences in their
GROUP 14. (ns np ) 2
2 first group to show complete range of properties, from nonmetal (C), through metalloids
(Si, Ge), to metals (Sn and Pb) – shows up in properties such as melting points and ΔH non fus
metals give strong covalent bonding ∴ higher melting points (Table 14.2)
Elements: show important allotropes for the first time in C chemistry: graphite (2D sheets),
diamond (3D network), C (molecular fullerenes, e.g., C , C , …). C looks like a soccer ball.
n 60 70 60
e.g., diamond graphite
very hard soft and greasy (used as lubricant)
3D 2D sheets
Graphite is the standard state of C at 298 K and 1 atm. Diamond formed at high T and P and
interconverts to graphite at 298 K (1 atm), but very slowly.
Oxidation states: multiple ones now more common!
C: nonmetal: compounds all covalent except C (carbide) ion e.g. Ca C. Oxide 2
(CO )2acidic: almost all oxid. states from 4 to +4 (e.g., CH to C4 ) know2.
Si, Ge: metalloids: essentially all compounds +4 ox. state, but some +2.
Sn, Pb: metals +4 (covalent) e.g., MO 2
+2 (ionic usually) e.g., MO
C usually fourcoordinate (exception C≡O). Other elements show more exceptions (e.g., SiF , 6
GeCl ,6Sn(OH) , Pb6OH) , but st6ll usually fourcoordinate. Why this difference between C
and the rest? C has 2s 2p outer configuration with no available d orbitals. Remainder of
elements have d orbitals they can use in bonding ∴ can form six bonds (sp d hybrids). 2
As we saw for the other groups , there is a big difference between C and rest of the
group. Main differences:
(i) ability to form low (down to 4) oxidation states
(ii) forms multiple bonds to itself or other light elements (N, O) e.g. CO (i.e. O2C=O), acetone
(i.e. (CH 3 2=O)
(iii) forms stable/common single bonds to itself (“catenation” = chain formation). e.g. nbutane
is H 3CH C2 –CH 2conta3ning a CCCC chain.
3 Include O, N, S, etc. and you have Organic Chemistry and Biochemistry! – and Life.
πbonding: C is small, forms strong enough π bonds to give stable compound