Metallic bond

● For any metal atoms, the outermost shell/ valence electron(s) are loosely held by the nucleus due to low ionisation energy. ● They can then overcome the nuclear attraction easily and become delocalized, leaving positive metal ions. The valence electrons are not shared between two atoms, but they float “freely” through the giant lattice of metal ions.

The electrostatic attraction between the positive metal ions and the sea of delocalized electrons.

● Ionic radius of metal ion increases ● Charge density decreases ● Weaker electrostatic force of attraction between the metal ion and the delocalized electrons ● Less energy is required to overcome the attraction ● Melting point decreases

● Melting point increases from group 1, 2 to group 3(13) metals ● Affected by two factors: (1) Charge of metal ion (2) Number of valence electrons per metal atom

(1) Charge of metal ions ● As the charge on metal ion becomes greater ● Stronger electrostatic force of attraction to the delocalized electrons ● Larger amount of energy is required to break the attraction ● Increasing melting point

(2) Number of valence electrons per metal atom ● Number of delocalised electrons per atom increases ● Stronger electrostatic force of attraction to the positive metal ions ● Larger amount of energy is required to break the attraction ● Increasing melting point

● Metals are good conductors of electricity. ● When an electrical circuit is closed, a voltage is set up. The delocalised electrons will be able to move in one direction (from negative to positive).

Malleability refers the ability of being reshaped under pressure.

Ductility refers to the ability of being pulled out into wires.

When a force is applied to a piece of metal, ● the layers of metal cations can slide past one another ● without breaking the metallic bonds (because the delocalised electrons still hold the metal cations together)

● Alloys are solid solutions (mixtures) of a metal with other elements. ● Ions of the different metals scattered through the lattice are bound by the delocalized electrons with metallic bonds. ● Alloys have properties that are distinct from their component elements.

brass (Cu copper and Zn zinc) bronze (Cu copper and Sn Tin) stainless steel (Fe iron, Ni nickel , Cr chromium)

● Metal cations have different ionic sizes, thus the regular packing of the metal cations is distorted. ● Layers of metal cations slide less easily

Enhanced properties of alloys 1. Increased strength (harder) 2. Decreased malleability and ductility 3. Lower electrical conductivity (movement of delocalised electrons affected)