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Bonding - Metallic
Metals have many uses.

Bonding - Metallic

This is the last of four GCSE Chemistry quizzes on bonding and it looks specifically at metallic bonding. It's difficult to imagine life without metals, we use them in practically every aspect of our lives. Virtually everything involves metals in some way but what makes them so useful? In a word - bonding. The arrangement of their atoms gives metals certain characteristics which are very useful to us. High melting and boiling points, reflection of light, conduction of heat and electricity - these are all properties that we take advantage of in some way.

In metals, the atoms are packed together really closely and this causes some of the outer electrons to break free and float around within the structure of the metal. We say that the electrons are delocalised. Because they have lost electrons, metal atoms are in fact metal ions, but you don't notice this because of the delocalised electrons. Since there are as many delocalised electrons as metal ions, the overall charge is still neutral.

Normally, the motion of the electrons is random and they can move anywhere in the metal. At GCSE level, the structure is often described as being 'metal ions in a sea of electrons'. The attraction between the 'sea' of electrons and the metal ions is very strong and we call it metallic bonding.

The positive metal ions are free to slide over one another and this makes metals malleable and ductile. The sea of electrons is spread throughout the metal, and so when it is pulled into wires, hammered to make it thinner or bent into a new shape, the overall composition and structure of the metal is not changed. The metal ions will have been rearranged but the sea of electrons adjusts to the new arrangement, keeping the metal intact. Some metals can be beaten into very thin sheets of foil without breaking. A good example of this is beating gold to make gold leaf. This can only be done because of metallic bonding.

The sea of electrons present in metallic bonding makes metals good conductors of heat. Heat is simply an area where particles have a greater kinetic energy (energy of movement) than their neighbours. So when you heat part of a piece of metal, the ions and electrons have more kinetic energy. The electrons will therefore move faster and further than they did when they were cooler, carrying the extra kinetic energy through the metal. At the same time, because the metal ions are so closely packed, they vibrate more and as they hit neighbouring ions, they too transfer the heat through the metal.

Metallic bonding also helps to explain why metals are able to conduct electricity. If you connect a piece of metal to an electrical potential difference (a voltage) e.g. an electrical cell, the electrons will move from the negative pole to the positive pole. So now the movement of electrons is less random and they all flow in the same direction through the metal which we recognise as an electrical current. Electrons are also affected by magnetic fields so when a metal is moved in a magnetic field, the delocalised electrons all tend to move in the same direction - this is how a generator or dynamo works.

Have a go at this final quiz on bonding and see how well you understand the arrangement of atoms in metallic bonding.

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1.
What does malleable mean?
Can be stretched into wires
Can be bent or hammered into shape
Is easily shattered
Is shiny
Most metals are malleable
2.
Metals are malleable because...
a large amount of energy is required to slide one layer of electrons over another
little energy is required to slide one layer of electrons over another
little energy is required to slide one layer of ions over another layer
a huge amount of energy is required to slide one layer of ions over another layer
You can immediately dismiss the first two options because they are talking about layers of electrons. In metallic bonding, it is the metal ions that are in layers, the electrons are randomly arranged
3.
Why do metals conduct electricity?
The positive metal ions are free to move
The negative electrons are free to move
All the constituent parts can move through the metal
The positive protons are free to move
The electrons that make up the 'sea' of delocalised electrons are free to move. This allows conduction of both heat and electricity
4.
Pick the correct statement about the arrangement of particles in a metal.
The particles are arranged randomly and far apart
The particles are arranged regularly and far apart
The particles are arranged regularly and close together
The particles are arranged randomly and close together
Metals usually have higher densities than non-metals because the particles are so closely packed together
5.
If a potential difference is applied to a metal...
the fixed electrons will stay in place and no current will pass through the metal
the negative ions will move through the metal carrying the electrical current
the delocalised ions will move through the metal carrying the electrical current
the delocalised electrons will move through the metal carrying the electrical current
They are attracted to the positive pole. As they leave the metal, fresh electrons are added via the negative pole
6.
Metals have...
low melting points because they have weak bonds
low melting points because they have strong bonds
high melting points because they have weak bonds
high melting points because they have strong bonds
The strong bonds make it more difficult for the particles to move further apart - requiring more energy - raising the melting point. There are exceptions and the metal mercury is already molten at room temperature
7.
One drawback of superconductors is...
their behaviour is erratic
they only work at VERY low temperatures
they could enable super fast transmission of electricity
they could enable loss free power transmission
To put metals into a superconducting state, extremely low temperatures close to absolute zero are required. If it becomes possible to make superconductors that work at temperatures above 0oC it would really change the world
8.
The bonding in metals is due to a strong attraction between...
positive metal ions and a sea of negative electrons
positive metal atoms and a sea of negative electrons
negative metal atoms and a sea of positive electrons
negative metal ions and a sea of negative electrons
Remember that opposites attract
9.
Superconductors...
work at any temperature
conduct heat better than other materials
have little or no resistance
conduct an orchestra really well
In conductors, electrical energy is lost because of the heating effect caused by resistance. In a superconductor, hardly any electrical energy is lost making electricity transmission much more efficient
10.
What type of bonding is present in metals?
Covalent
Ionic
Hydrogen
Metallic
The majority of elements have this type of bonding
Author:  Kate Gardiner

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