Chem Bonding [Lattices]

What is the structure of a giant ionic lattice?

• Constituent ions held in fixed positions in an orderly arrangement

• Arranged such that that attraction is maximum and repulsion is minimum

• Ionic bonds are non-directional

What is an ionic bond?

Electrostatic force of attraction between cations and anions

• Strong and a lot of energy is required to break such bonds

• Strength indicated by lattice energy

What is lattice energy?

Energy released when one mole of ionic crystalline solid is formed from its constituent gaseous ions

• Greater magnitude → stronger ionic bond

• Proportional to |(q+ x q-) / (r+ + r-)|

  • Higher charge (greater EFA) + smaller radius (shorter inter-ionic distance between ions) → greater attraction

What are physical properties of ionic compounds? (4)

• High melting and boiling points ← large amounts of energy required to break strong ionic bonds

• Generally soluble in polar (aq) solvents but insoluble in non-polar (org) solvents

• Conducts electricity in molten and aqueous states but not in the solid state ← Dissociation to form free-moving ions / Strong enough force to form free-moving ions

• Hard and brittle

  • Strong attraction → Strong repulsion

  • Displacement along cleavage plane → Ions of like charges are opposite each other

What are well-known examples of giant molecular lattices?

Diamond, graphite, quartz (silicon dioxide), silicon carbide, boron nitride

What are physical properties of giant molecular lattices (generally)?

• High melting and boiling point ← Strong covalent bonds between atoms

• Does not conduct electricity ← Absence of mobile charge carriers

• Insoluble in all solvents

• Hard

What are the special properties of graphite?

• Weak intermolecular forces between layers that can slide over each other → Used in pencils and lubricants

• Electrical conductivity → Each C atom is bonded to 3 other C atoms

What are the physical properties of a simple molecular lattice? (4)

• Low melting and boiling points ← weak IMF between atoms

• Soluble in non-polar(org) solvents but insoluble in polar(aq) solvents ← Soluble due to the solute and solvent having the same type of intermolecular attraction

• Does not conduct electricity in solid or molten state, but may in aqueous state ← ionizes in water e.g. Hal, AlCl3, ethanoic acid

• Soft

What is a metallic bond?

Electrostatic attraction between a lattice of positive ions and delocalized electrons

• Strong and non-directional

What factors affect the strength of a metallic bond?

• Number of valence electrons available

  • Greater number of valence electrons → Stronger bond

• Charge of cations

  • Higher charge → Stronger bond

• Size of cations

  • Smaller size → Stronger bond

  • High charge density

What are the physical properties of metals? (6)

• High electrical conductivity, even as solids ← Delocalised electrons = charge carriers

• Good thermal conductivity ← Electrons collide to pass thermal energy

• Hard but malleable and ductile ← Cation layers glide over each other easily without breaking the bond

• High density ← Closely-packed ions

• High melting and boiling points ← Strong EFA between the ions

• Soluble only in liquid metals