Factors Affecting Bond Strength, Trends in Melting Points, and Formation of Alloys
Definition
Alloy
An alloy is a mixture of a metal with one or more other elements, which can be either metals or non-metals
Factors Affecting Bond Strength in Metals
- The strength of metallic bonds arises from the electrostatic attraction between positively charged metal cations and the "sea" of delocalized electrons surrounding them.
- Two key factors influence this attraction: the charge of the cations and the radius of the cations.
Charge of Cations
- The charge of a metal cation directly affects the strength of the metallic bond.
- Cations with higher charges exert a stronger pull on the delocalized electrons, increasing the bond strength.
- Sodium (Na) forms cations with a charge of $1+$.
- Magnesium (Mg) forms cations with a charge of $2+$.
- Aluminium (Al) forms cations with a charge of $3+$.
- As the charge increases from $1+$ to $3+$, the metallic bond becomes stronger.
- This explains why aluminium has a higher melting point than magnesium or sodium.
Radius of Cations
- The size of the cation plays an equally important role.
- Smaller cations allow the delocalized electrons to get closer to the nucleus, increasing the strength of the electrostatic attraction.
- Sodium cations ($Na^+$) have a larger ionic radius than magnesium cations ($Mg^{2+}$).
- Magnesium cations are larger than aluminium cations ($Al^{3+}$).
- This trend helps explain why aluminium, with its small cation radius and high charge, forms the strongest metallic bonds among these three metals.
- Don’t confuse the size of the neutral atom with the size of the cation.
- When a metal atom loses electrons to form a cation, its radius decreases significantly.
Trends in Melting Points of Metals
- The melting point of a metal reflects the strength of its metallic bonds.
