ppt summary on metal structure, bonding and properties

2. Mostly found as ORES combined with non-metal elements. Metal + non-metal = IONIC COMPOUNDS

4. Useful properties that are not found in any other materials.

5. Metals are used where strength of a material is an important factor.

7. Why are metals lustrous? Why do we see a perfect (but laterally inverted) image in a plane mirror (silvered glass)?

8. metals covalent molecular covalent network covalent layer IONIC BONDING (microscopic) STRUCTURE & names (Symbolic) PROPERTIES (macroscopic)

11. Metal elements have: 1, 2 or 3 valence electrons. E.g. Magnesium 12: 2,8,2 To be stable they lose this last electron and become positively charged according to how many they lose N O F Ne Na 12p + Mg 2+

12. Since metal atoms have low electronegativities and they want to be more stable, the outer shell/ valence electron jumps out. These delocalised e-s form the pool/sea of delocalised e-s. (note: the language of pool/sea).

13. Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+ Mg 2+

15. YOU DRAW

16. Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ Mg+ METAL LATTICE Electrostatic attraction between CATIONS & Delocalised e- (sea of e-) (e-s free to move)

18. PROPERTIES

19. PROPERTIES EXPLAINED BY THE STRUCTURE

20. E- can absorb quantum of energy and become excited When they fall back they release it as light Metal lattice contains ‘ Free’ e- = almost all differences of energy levels can be absorbed and re-emitted = almost all visible light reflected. = Lustrous (shiny) 1

21. Every electron can absorb a specific quantum or packet of radiation to become excited . "Free" electrons often absorb quanta of visible light. In metals the outer electrons are essentially "free" electrons and their energy depends on their distance from a nucleus; as there are countless "free" electrons of almost every possible extranuclear distance and energy they can absorb all the visible light that falls on the metal surface. However an excited electron re-emits the same absorbed quantum of radiation as it becomes de-excited and most of the radiation that is incident on a metal surface is expelled from the surface thus: metals are highly reflective or lustrous . 1

22. WHAT IS HAPPENING? (discuss) Good conductor of heat 2

24. Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow WHAT IS HAPPENING? (discuss) 3

25. Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow Current = flow of charge Sea of electrons = free to move 3

26. WHAT IS HAPPENING? (discuss) 4

28. High melting and boiling point To break the lattice the bonds must be broken. The electrostatic force between the sea of electrons and the cations is very strong. Thus it requires lots of energy, therefore it has high melting point and it is hard. (note: the more delocalised electrons the stronger these properties) The cations and electrons are closely packed together b/c strong… High density 5

36. Heat treatment Consistent small crystals Smaller crystals Larger crystals Retains hardness, reduce brittleness. Quenched, warmed again to a lower temperature, cool slowly. Tempered Harder but more brittle (e.g. horseshoes) Heated to red hot, Cooled quickly (in cold water) Quenched Softer (restores ductility) Heated to red hot, cooled slowly Annealed

38. Ni-Cu alloy Magnetic alloys are at the heart of a wide range of technological applications from the oldest of structural materials to the next generation of data storage and retrieval devices.