Semiconductors

1. 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? 4. What is the conductor band? 5. Will conduction occur with filled, partially filled or empty bands? Elements from which group are used in p-type doping? Conduction involves the movement of what in p-type semiconductors? Elements from which group are used in n-type doping? What moves during conduction? MM 2006 AH Chemistry Unit 1

2. 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

3. Oxides Generally can be prepared by direct combination of elements with oxygen spontaneous e.g. alkali metals e.g. magnesium slowly at room temperature occurs on heating e.g. carbon high temperature e.g. nitrogen MM 2006 AH Chemistry Unit 1

4. Period 2 Period 3 2 4 1 3 5 7 6 Melting points of period 2 & 3 oxides MM 2006 AH Chemistry Unit 1

5. Li Be B C O F N Na Al Si S Cl Mg P ionic lattice ionic/covalent network covalent network covalent molecular Types of bonding in oxides Electrical conductivity Melts or solutions of ionic oxides MM 2006 AH Chemistry Unit 1

6. Li Be B C O F N Na Al Si S Cl Mg P forms an alkali forms a weak alkali e.g. Na2O(s) + H2O (l) NaOH(aq) no reaction/insoluble forms an acid e.g. NO2 (s) + H2O (l) H NO3(aq) slightly soluble but no reaction ‘Reaction’ of oxides with water MM 2006 AH Chemistry Unit 1

7. Li Be B C O F N Na Al Si S Cl Mg P basic weakly basic Al2O3 + 6HCl 2AlCl3 + 3H2O amphoteric Al2O3 + 3H2O + NaOH 2NaAl(OH)4 acidic neutral Acid/base character of oxides MM 2006 AH Chemistry Unit 1

8. 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

9. Li Be B C O F N Na Al Si S Cl Mg P Types of bonding in chlorides ionic lattice partially covalent network covalent molecular Electrical conductivity melts or solutions of ionic chlorides MM 2006 AH Chemistry Unit 1

10. Li Be B C O F N Na Al Si S Cl Mg P ‘Reaction’ of chlorides with water soluble insoluble/immiscible produces fumes of hydrogen chloride e.g. PCl5 (s) + 4H2O (l) H3PO4(aq) + 5HCl (aq) MM 2006 AH Chemistry Unit 1

11. Li Be B C O F N Na Al Si S Cl Mg P weakly acidic acidic neutral Acid/base character of chlorides MM 2006 AH Chemistry Unit 1

12. Reaction with sodium hydride produces the metal from many metal oxides e.g. CuO + NaH Cu + NaOH Hydrides H- ion very strong base/reducing agent e.g. 2KH(s) + 2H2O(l) H2(g) + 2KOH(aq) Lithium aluminium hydride (LiAlH4) and sodium tetrahydroborate (NaBH4) used in organic chemistry when strong reducing agents required MM 2006 AH Chemistry Unit 1

13. Li Be B C O F N Na Al Si S Cl Mg P Types of bonding in hydrides ionic lattice ionic/covalent polymeric covalent molecular Electrical conductivity when molten good non-conductors poor MM 2006 AH Chemistry Unit 1

14. Li Be B C O F N Na Al Si S Cl Mg P forms hydroxide and hydrogen insoluble soluble forms hydroxide ‘Reaction’ of hydrides with water MM 2006 AH Chemistry Unit 1

15. Li Be B C O F N Na Al Si S Cl Mg P strongly alkaline alkaline weakly alkaline neutral weakly acidic strongly acidic Acid/base character of hydrides MM 2006 AH Chemistry Unit 1