Metallic Bonding and Properties
Metallic bonding explains how metal atoms are held together in a giant structure, which in turn determines their characteristic properties like high conductivity and melting points. Understanding this model is key to predicting the behaviour of metallic elements.
Part of the ESAT Chemistry syllabus — revision for the Engineering and Science Admissions Test (ESAT), the UAT-UK admissions test for Cambridge, Imperial, Oxford and UCL.
Key points
- Metals consist of a giant, regular lattice of positively charged metal ions.
- The outer shell electrons from each metal atom are delocalised, meaning they are free to move throughout the entire structure, forming a 'sea' of electrons.
- Metallic bonding is the strong electrostatic force of attraction between the positive metal ions and the negative sea of delocalised electrons.
- The mobility of the delocalised electrons allows metals to conduct electricity and heat efficiently in both solid and liquid states.
- A large amount of energy is needed to overcome the strong electrostatic attractions, which is why most metals have high melting and boiling points.
- Metals are typically malleable and ductile because the layers of positive ions can slide over one another without disrupting the metallic bond.
Definitions
- Metallic Bonding
- The electrostatic attraction between a regular lattice of positive metal ions and the surrounding 'sea' of delocalised electrons.
- Delocalised Electrons
- Electrons that are not associated with any single atom or bond and are free to move throughout the entire metallic structure.
Worked example
Aluminium is a metal with a melting point of 660°C and is an excellent electrical conductor. Which of the following statements provides the best explanation for these properties?
- 1
Step 1:
Identify the bonding in aluminium.
As a metal, it exhibits metallic bonding.
- 2
Step 2:
Recall the model of metallic bonding.
It consists of positive ions (Al³⁺) in a fixed lattice surrounded by a 'sea' of mobile, delocalised electrons.
- 3
Step 3:
Relate the properties to this model.
Electrical conductivity is due to the presence of mobile charge carriers, which are the delocalised electrons.
- 4
Step 4:
A high melting point indicates that the forces holding the structure together are strong.
In the metallic model, this is the strong electrostatic attraction between the positive Al³⁺ ions and the delocalised electrons.
- 5
Step 5:
Therefore, the best explanation must involve both strong electrostatic forces and mobile delocalised electrons.
Answer: The properties are due to strong electrostatic forces between positive aluminium ions and a sea of delocalised electrons, where these electrons are free to move and carry charge.
Common mistakes
- ×Confusing the properties of metals with ionic compounds. Metals conduct electricity as solids, whereas ionic compounds only conduct when molten or dissolved.
- ×Incorrectly describing the bonding force as being between the positive metal ions. The attraction is between the positive ions and the negative delocalised electrons.
- ×Giving a vague explanation for high melting points, such as 'strong bonds', without specifying the nature of the attraction (electrostatic) and the particles involved (ions and delocalised electrons).
No-calculator tips
- ✓For questions involving tables of properties, identify metals by looking for good conductivity in BOTH the solid and liquid state.
- ✓Always link conductivity directly to 'mobile delocalised electrons' or 'sea of electrons'.
- ✓Always link high melting/boiling points to 'strong electrostatic attraction' between positive ions and delocalised electrons.