Delocalised electrons and giant metallic structures, why metals conduct and can be shaped, and why alloys are harder than pure metals.
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1.Describe the structure of a metal.
A giant structure of positive metal ions arranged in a regular pattern, surrounded by a sea of delocalised electrons.
2.What does delocalised mean?
The electrons are not attached to any one atom and are free to move throughout the whole structure.
3.Where do the delocalised electrons come from?
The outer shell of each metal atom, which is why the atoms become positive ions.
4.Define metallic bonding.
The strong electrostatic attraction between the positive metal ions and the delocalised electrons.
5.Why do metals have high melting and boiling points?
The metallic bonds between the ions and the delocalised electrons are strong, so a lot of energy is needed to break the structure apart.
6.Why do metals conduct electricity?
The delocalised electrons are free to move through the structure and carry the charge.
7.Why do metals conduct thermal energy well?
The delocalised electrons move freely and transfer energy quickly through the structure.
8.Why can pure metals be bent and shaped?
The atoms are arranged in layers that can slide over one another.
9.What is an alloy?
A mixture of a metal with at least one other element, usually another metal.
10.Why are alloys harder than pure metals?
The different sized atoms distort the layers, so they can no longer slide over each other easily.
11.Give an example of an alloy and what it is made from.
Steel is made from iron and carbon. Bronze is copper and tin. Brass is copper and zinc.
12.Why is pure gold not used for jewellery?
It is too soft and would be damaged easily, so it is alloyed with other metals to harden it.
13.Are alloys compounds or mixtures?
Mixtures. The elements are not chemically bonded to one another in fixed proportions.
14.Why are metals malleable?
The layers of ions can slide over each other without breaking the metallic bonding, because the delocalised electrons hold the structure together throughout.
15.What does malleable mean?
It can be hammered or rolled into shape without shattering.
16.What does ductile mean?
It can be drawn out into a wire.
17.Compare metallic and ionic bonding.
Both involve strong electrostatic attraction. In ionic bonding it is between positive and negative ions; in metallic bonding it is between positive ions and delocalised electrons.
18.Why do ionic solids not conduct but metals do?
In an ionic lattice all the electrons are held in ions in fixed positions. In a metal the delocalised electrons are free to move.
19.Why do metals have a shiny appearance when freshly cut?
The delocalised electrons at the surface reflect light.
20.Why are alloys generally more useful than pure metals?
They can be made harder, stronger or more resistant to corrosion, so they can be designed for a particular purpose.
21.What happens to the delocalised electrons when a metal is bent?
Nothing changes about them. They continue to hold the structure together as the layers move, which is why the metal does not break.
22.Which particles carry the current in a metal?
The delocalised electrons.
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