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 12p + Mg 2+
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).
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
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
WHAT IS HAPPENING? (discuss) Good conductor of heat 2
When atoms absorb heat energy they vibrate (temperature is a measurement of molecular energy) and this vibration is passed from one atom to the next.
In metals, because the metal atoms are often close packed together the vibration or heating effect is passed rapidly through the metal from one atom to another. Also electrons are free to move so will bump and transmit this energy rapidly.
Note: flow of current is the flow of positive charge, i.e. opposite direction of electron flow WHAT IS HAPPENING? (discuss) 3
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
4 Metallic Lattice Electrostatic attraction b/w cations and sea of electrons still present after deformation. Ionic Lattice Electrostatic attraction b/w cations and anions broken
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
Limitations of structure/properties Examples of some exceptions
More brittle (e.g. keep bending a metal wire, it goes harder, then it snaps.)
Bend a wire. What happens?
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