Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Metallic bonding is the electrostatic attraction between a lattice of positive metal ions () and a 'sea' of delocalized valence electrons.
The strength of the metallic bond depends on the charge density of the metal ions. It increases with an increase in the number of valence electrons (charge ) and a decrease in the ionic radius ().
Metals are excellent electrical conductors because the delocalized electrons are free to move throughout the lattice when a potential difference is applied.
Thermal conductivity in metals is high because both the delocalized electrons and the vibrations of the closely packed ions facilitate the transfer of kinetic energy.
Malleability and ductility arise because the metallic bond is non-directional; layers of ions can slide over each other without breaking the bond, as the 'sea' of electrons acts as a flexible glue.
Alloys are solid solutions or mixtures of a metal with other elements (metals or non-metals, such as Carbon in Steel). Alloys are usually harder than pure metals because atoms of different sizes disrupt the regular lattice structure, preventing layers from sliding easily.
📐Formulae
💡Examples
Problem 1:
Explain why Aluminum () has a higher melting point than Sodium ().
Solution:
has a melting point of approximately , while has a melting point of approximately .
Explanation:
Aluminum forms ions and contributes three delocalized electrons per atom to the 'sea', whereas Sodium forms ions and contributes only one. The ion has a higher charge and a smaller ionic radius than , resulting in a much higher charge density. This leads to a stronger electrostatic attraction between the cations and the delocalized electrons, requiring more energy to break the lattice.
Problem 2:
Why is Brass (an alloy of and ) harder than pure Copper ()?
Solution:
The addition of atoms into the lattice creates irregularities.
Explanation:
In pure , the atoms are of uniform size and arranged in regular layers that can easily slide over one another when force is applied. In Brass, the atoms have a different atomic radius than . These differently sized atoms distort the regular lattice layers, making it significantly more difficult for the layers to slide over each other, thus increasing the hardness of the material.