Metallic bonding and alloys

Science · Matter & Materials · ages 15-16

Name ______________________ Date ____________

Why can copper be hammered flat instead of shattering?
- the hammer knocks the electron sea out of the metal
- the hammer is softer than the copper underneath it
- copper is a liquid at very low temperatures
- its layers of identical ions slide over each other
In a metal the electrons are shared across the whole piece rather than between two atoms.
Circle one: True False
How many different elements are there in a piece of pure copper?
Answer: ______________
An aluminium atom is 2,8,3. How many electrons does one aluminium atom put into the sea?
Answer: ______________
Magnesium is in group 2. A sample holds 100 magnesium atoms. How many electrons are in its sea?
Answer: ______________
Solder is an alloy chosen partly because it melts at a fairly low temperature. Why does that matter on a circuit board?
- a low melting point makes the joint conduct better
- a hotter soldering iron would damage the components
- the board itself is made of metal and would melt too
- molten solder cannot conduct until it has fully cooled
A sample of brass is 70 per cent copper and the rest zinc. What percentage of it is zinc?
Answer: ______________
Adding a different-sized atom to a metal makes its layers slide more easily.
Circle one: True False
Asked why copper wire conducts, Priya answers that the copper ions travel along the wire. Where is the slip?
- copper forms no ions in the metal at all
- the ions carry no charge, so they cannot conduct
- copper wire does not actually conduct electricity by itself
- the ions are locked in place by the sea and only vibrate
A metal gives up 3 electrons per atom. A sample holds 50 of its atoms. How many positive charges are carried by the ions altogether?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

Metallic bonding and alloys W1-mt_yXOGOwHmZ4-s1

its layers of identical ions slide over each other · Every ion is the same size, so a layer can move one place along and still fit. The electron sea moves with it, so the metallic bond is never broken.
True · That is what delocalised means. A covalent bond ties a pair of electrons to two particular atoms; a metal's electrons belong to no pair at all.
1 · Pure means one element only. That is exactly why the layers slide so easily: every ion in every layer is the same size.
3 · It gives up its whole outer shell, which holds 3 electrons. That leaves an aluminium ion carrying a charge of 3+.
200 · Each atom gives up its 2 outer electrons, so 100 atoms give 100 x 2 = 200 electrons into the shared pool.
a hotter soldering iron would damage the components · The soldering iron has to melt the solder without cooking the chips beside it. Choosing a mixture that melts low keeps the rest of the board safe.
30 · The two shares fill the hundred between them, so 100 - 70 = 30 per cent zinc.
False · It does the opposite. Uneven layers catch on each other instead of sliding, which is exactly why an alloy is harder than the pure metal.
the ions are locked in place by the sea and only vibrate · The ions vibrate but keep their places, which is why a wire does not slowly get shorter at one end. The delocalised electrons are what move through it.
150 · Each atom becomes a 3+ ion, so 50 ions carry 50 x 3 = 150 positive charges. Those are matched exactly by the 150 electrons in the sea.