AS-Level Chemistry Chapter 4 Chemical Bonding Metallic Bonding

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Metallic Bonding

Metallic bonds

1) Metallic bond is the electrostatic force of attraction between the delocalized electrons and the positive metal ions.

2) Take sodium as an example, in the solid state, sodium atoms are packed so closely together that the 3s orbitals(containing an electron) overlap with one another to form a giant molecular orbital.

3) The 3s electrons is then free to move throughout the lattice structure, it is no longer bound to any sodium atom. The electrons are said to be delocalized. The delocalized electrons are sometimes referred to as 'sea of delocalized electrons'.

4) The attraction between the delocalized electrons and the positive metal ions constitutes the metallic bond.

Factors affecting the strength of metallic bonds

1) Number of electrons in the sea of delocalized electrons

- The more the number of electrons delocalized, the stronger the metallic bond.
- For example, the melting point of magnesium is higher than sodium.
- This is because one magnesium atom can donate two electrons from its outer shell into the sea of delocalised electrons while sodium can only donate one.
- There is twice amount of delocalised electrons in magnesium than in sodium.

So, the metallic bond in magnesium is stronger due to the stronger attraction.

2) Size of the metal

- The smaller the size of the metal, the stronger the metallic bond.
- For example, the melting point of magnesium is lower than beryllium although both of them have two electrons delocalized per atom.
- This is because the size of magnesium is bigger, causing the attraction between the delocalized electrons and the positive nucleus to be weaker. The shielding effect in magnesium is also more than in beryllium.
- So, the metallic bond in magnesium is weaker than in beryllium.