This chemistry grades 9-10 lesson on metallic bonding notes gives the key ideas first, then worked examples and diagrams. After that, practise with the worksheet on metallic bonding and check yourself with the quiz.
Quick answer: Metallic bonding is the attraction between positive metal ions in a regular lattice and a sea of delocalised electrons that move freely between them. It explains why metals conduct electricity and heat, can be hammered into shape, and have high melting points. Alloys are harder because different-sized atoms stop layers sliding.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE C2
Metallic bonding notes: the key ideas
What is metallic bonding?
Metal atoms have few outer electrons, and they release them easily. In a piece of metal each atom gives up its outer electrons, which are no longer tied to any one atom. The atoms become positive ions arranged in regular layers, and the released electrons form a sea that moves freely between them.
A metallic bond is the electrostatic attraction between positive metal ions and the sea of delocalised electrons around them. Delocalised electrons belong to the whole structure, not to a single atom.
The metal as a whole is neutral, because the number of electrons equals the number of positive charges on the ions.
Why do metals conduct and bend without breaking?
The metallic bond explains the typical properties of metals.
| Property | Explanation |
|---|---|
| Conducts electricity | Delocalised electrons move through the metal and carry charge. |
| Conducts heat | Free electrons pass energy quickly, and vibrating ions pass it on to their neighbours. |
| High melting point | The attraction between ions and electrons is strong and needs a lot of energy to overcome. |
| Malleable and ductile | Layers of ions slide over each other while the electrons keep holding them together. |
Metals also look shiny because the free electrons reflect light, and most are dense because the ions pack closely together. Melting a metal does not remove the electron sea, so liquid metals still conduct electricity.
Metals do not conduct because ions flow. The positive ions stay in their layers, and only the electrons move. Also, the sea of electrons does not make the metal negative, because the ions carry an equal amount of positive charge.
Explain why magnesium (melting point 650 °C) melts at a much higher temperature than sodium (98 °C).
A sodium atom has 1 outer electron, so it forms Na⁺ and gives 1 electron to the sea. A magnesium atom has 2 outer electrons, so it forms Mg²⁺ and gives 2 electrons. Mg²⁺ ions have a bigger charge and there are more electrons in the sea, so the attraction is stronger.
Answer: a stronger metallic bond needs more energy to overcome, so magnesium has the higher melting point.
What is an alloy and why is it harder than a pure metal?
An alloy is a mixture of a metal with at least one other element, often another metal. Pure metals are soft because their identical atoms form neat layers that slide easily. In an alloy, atoms of a different size disturb the layers, so the layers cannot slide so easily and the material is harder and stronger.
| Alloy | Made from | Typical use |
|---|---|---|
| Brass | copper and zinc | taps, door handles, musical instruments |
| Bronze | copper and tin | bells, statues, ship propellers |
| Steel | iron and carbon | bridges, rails, bicycle frames |
| Duralumin | aluminium and a little copper | aircraft parts |
A ring is made of 18-carat gold and has a mass of 9.0 g. Carats show the number of parts of gold in 24 parts. Calculate the mass of gold.
Fraction of gold = 18 ÷ 24 = 0.75. Mass of gold = 0.75 × 9.0 g = 6.75 g.
Answer: 6.75 g of gold (about 6.8 g).
To explain why a metal bends, draw layers of ions with the electron sea around them. Then draw one layer moved along by a position: the picture looks the same, which shows that the bonding survives.
- Metallic bond = attraction between positive ions and delocalised electrons.
- Free electrons carry charge and energy, so metals conduct electricity and heat.
- Layers of ions slide without breaking the bonding, so metals are malleable and ductile.
- More delocalised electrons and a higher ion charge give a stronger bond and a higher melting point.
- An alloy contains atoms of different sizes, so its layers slide less easily than those of a pure metal.
Ions in a sea of electrons: frequently asked questions
What are delocalised electrons?
Delocalised electrons are outer electrons that are not attached to a single atom. They move freely through the whole metal structure and carry electric charge and thermal energy.
Why can metals be hammered into sheets?
The layers of positive ions can slide over each other. The sea of electrons keeps attracting the ions in their new positions, so the metal changes shape without breaking.
Why do metals have high melting points?
Every ion is strongly attracted to the electron sea in all directions. Melting needs enough energy to loosen this strong attraction, so the temperature must be high.
What is the difference between a pure metal and an alloy?
A pure metal contains one kind of atom. An alloy is a mixture of a metal with other elements, and its different-sized atoms make it harder than the pure metal.
Why does steel last longer than pure iron?
Steel contains a small amount of carbon. The carbon atoms disturb the iron layers, so they resist sliding, which makes steel stronger and harder than pure iron.
