The document discusses the atomic structure and properties of metals, insulators, and semiconductors. Metals conduct electricity well due to their free electrons, are shiny as electrons scatter light, and are stiff yet ductile from electron bonding. Insulators like ceramics and polymers do not conduct as their electrons are locked in ionic or covalent bonds, making them stiff or brittle. Semiconductors have properties between metals and insulators with fewer free electrons. Their conductivity increases with temperature unlike metals but can also be controlled through doping with other atoms to donate or accept free electrons.

1. Atomic Structure and Properties Today we will discuss: The structure of metals, insulators and semi-conductors and how this affects: Electrical properties Appearance Mechanical properties 29 May 2009

2. Metals Metals - Because the free electrons in metals: conduct well - are mobile and carry current are shiny - oscillate in light, scattering light photons are stiff - ‘glue’ ions together strongly are ductile - provide non-directional glue, letting ions slip All atoms are ionised and the electrons are free to move…

3. Insulators - Ceramics Ceramics - Because the ionic bonds holding them together: are insulators - lock electrons to ions or atoms, so none are free to move are stiff - are hard to stretch strong bonds are brittle - are directional bonds, so that atoms or ions cannot slip Electrons lock to ions so none are free to move…

4. Insulators - Polymers Polymers - Because the covalent bonds stringing monomers in long chains: are insulators - lock electrons to atoms, with none free to move are often flexible- can rotate, letting chains stretch or fold are often plastic – make chains which can slip past one another The covalent bonds, stringing monomers into long chains…

5. Semi-Conductors These have properties in-between: Metals and Insulators These have far fewer ionised atoms (and hence fee electrons)

6. Semiconductors and Conductivity

7. But what happens… When things get hot!!!?!?!?!? Using a beaker, tripod, multimeter, a piece of wire and a semiconductor sample (thermistor), test: The effect of temperature on conductivity (measure resistance) of metals and semiconductors…

8. What is happening…?

9. Doping Obviously it is not practical to heat up semiconductors – to increase conductivity we ‘dope’ them with other atoms. Using page 124 summarise, with pictures, the 2 types of doping