semiconductors
DESCRIPTION
Semiconductors. 1. Where in the Periodic Table would you find semiconducting elements?. Increasing temperature has what effect on the conductivity of : i) metals ii) superconductors iii) semiconductors?. 3. Which term describes the highest occupied energy band?. - PowerPoint PPT PresentationTRANSCRIPT
MM 2006 AH Chemistry Unit 1
Semiconductors
2. Increasing temperature has what effect on the conductivity of :
i) metals ii) superconductors iii) semiconductors?
1. Where in the Periodic Table would you find semiconducting elements?
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?
3. Which term describes the highest occupied energy band?
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
OxidesGenerally can be prepared by direct combination of
elements with oxygen
spontaneous
slowly at room temperature
occurs on heating
high temperature
e.g. alkali metals
e.g. magnesium
e.g. carbon
e.g. nitrogen
MM 2006 AH Chemistry Unit 1
Melting points of period 2 & 3 oxides
3000
2500
2000
1500
1000
500
0
-500
Melting point (oC)
Group
Series 1
Series 2
1 2 3 4 5 6 7
Period 2
Period 3
MM 2006 AH Chemistry Unit 1
Types of bonding in oxides
Electrical conductivity
Melts or solutions of ionic oxides
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
ionic lattice
ionic/covalent network
covalent network
covalent molecular
MM 2006 AH Chemistry Unit 1
‘Reaction’ of oxides with water
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
no reaction/insoluble
forms an acidslightly soluble but no reaction
forms an alkali e.g. Na2O(s) + H2O (l) NaOH(aq)
e.g. NO2 (s) + H2O (l) H NO3(aq)
forms a weak alkali
MM 2006 AH Chemistry Unit 1
Acid/base character of oxides
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
basic
amphoteric
acidic
neutral
Al2O3 + 6HCl 2AlCl3 + 3H2O
Al2O3 + 3H2O + NaOH 2NaAl(OH)4
weakly basic
MM 2006 AH Chemistry Unit 1
ChloridesCan 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
Electrical conductivitymelts or solutions of ionic chlorides
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
ionic lattice
partially covalent network
covalent molecular
MM 2006 AH Chemistry Unit 1
‘Reaction’ of chlorides with water
Na
Li
Mg
Be
Al
B C N O F
Si P S 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
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
weakly acidic
acidic
neutral
MM 2006 AH Chemistry Unit 1
HydridesH- 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
Electrical conductivitywhen molten
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
ionic lattice
ionic/covalent
polymeric
covalent molecular
good non-conductors poor
MM 2006 AH Chemistry Unit 1
‘Reaction’ of hydrides with water
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
forms hydroxide and hydrogen
insoluble
soluble
forms hydroxide
MM 2006 AH Chemistry Unit 1
Acid/base character of hydrides
Na
Li
Mg
Be
Al
B C N O F
Si P S Cl
strongly alkaline
alkaline
strongly acidic
neutral
weakly alkaline
weakly acidic