Semiconductors
1. Where in the Periodic Table would you find semiconducting elements?
2. Increasing temperature has what effect on the conductivity of :
i) metals ii) superconductors iii) semiconductors?
3. Which term describes the highest occupied energy band?
4. What is the conductor band?
5. Will conduction occur with filled, partially filled or empty bands?
6. Elements from which group are used in p-type doping?
Conduction involves the movement of what in p-type semiconductors?
7. Elements from which group are used in n-type doping?
What moves during conduction?
MM 2006 AH Chemistry Unit 1
Oxides, chlorides and hydrides of
the second and third periods
properties relate to position in the periodic table
trends in physical properties and chemical reactions with water
can be explained in terms of the changing nature of the bonding
moving across the periods
MM 2006 AH Chemistry Unit 1
Oxides
Generally can be prepared by direct combination of
elements with oxygen
spontaneous
e.g. alkali metals
slowly at room temperature e.g. magnesium
occurs on heating
e.g. carbon
high temperature
e.g. nitrogen
MM 2006 AH Chemistry Unit 1
Melting points of period 2 & 3
oxides
30 00
Series 1
Series 2
25 00
M
e
l
t
20 00
i
n
g
Period 2
15 00
p
o
i
Period 3
10 00
n
t
(
50 0
o
C
)
0
1
2
4
3
5
-500
Gro up
MM 2006 AH Chemistry Unit 1
6
7
Types of bonding in oxides
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
F
Cl
ionic lattice
ionic/covalent network
covalent network
covalent molecular
Electrical conductivity
Melts or solutions of ionic oxides
MM 2006 AH Chemistry Unit 1
‘Reaction’ of oxides with water
Li
Be
Na Mg
forms an alkali
B
Al
C
Si
N
P
O
S
e.g. Na2O(s) + H2O (l)
F
Cl
NaOH(aq)
forms a weak alkali
no reaction/insoluble
forms an acid e.g. NO2 (s) + H2O (l)
slightly soluble but no reaction
MM 2006 AH Chemistry Unit 1
H NO3(aq)
Acid/base character of oxides
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
F
Cl
basic
weakly basic
Al2O3 + 6HCl
2AlCl3 + 3H2O
amphoteric
acidic
Al2O3 + 3H2O + NaOH
neutral
MM 2006 AH Chemistry Unit 1
2NaAl(OH)4
Chlorides
Can be prepared by direct combination of elements with
chlorine or by reacting metals with hydrochloric acid
Bonding present in periods 2 and 3 varies in a similar way
to that of the oxides
MM 2006 AH Chemistry Unit 1
Types of bonding in chlorides
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
ionic lattice
partially covalent network
covalent molecular
Electrical conductivity
melts or solutions of ionic chlorides
MM 2006 AH Chemistry Unit 1
F
Cl
‘Reaction’ of chlorides with water
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
F
Cl
soluble
insoluble/immiscible
produces fumes of hydrogen chloride
e.g. PCl5 (s) + 4H2O (l)
H3PO4(aq) + 5HCl (aq)
MM 2006 AH Chemistry Unit 1
Acid/base character of chlorides
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
weakly acidic
acidic
neutral
MM 2006 AH Chemistry Unit 1
F
Cl
Hydrides
H- ion very strong base/reducing agent e.g.
2KH(s) + 2H2O(l)
H2(g) + 2KOH(aq)
Reaction with sodium hydride produces the metal from
many metal oxides e.g.
CuO + NaH
Cu + NaOH
Lithium aluminium hydride (LiAlH4) and sodium
tetrahydroborate (NaBH4) used in organic chemistry
when strong reducing agents required
MM 2006 AH Chemistry Unit 1
Types of bonding in hydrides
ionic lattice
ionic/covalent
polymeric
Li
Be
Na Mg
good
B
Al
C
Si
N
P
non-conductors
O
S
F
Cl
poor
MM 2006 AH Chemistry Unit 1
covalent molecular
Electrical conductivity
when molten
‘Reaction’ of hydrides with water
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
forms hydroxide and hydrogen
insoluble
soluble
forms hydroxide
MM 2006 AH Chemistry Unit 1
F
Cl
Acid/base character of hydrides
Li
Be
Na Mg
B
Al
C
Si
N
P
O
S
strongly alkaline
alkaline
weakly alkaline
neutral
weakly acidic
strongly acidic
MM 2006 AH Chemistry Unit 1
F
Cl