Bonding

• valency - number of electrons an atom has to lose, gain or share to attain a stable electronic structure
• ionic/electrovalent bonding - bonding of a metal and a non-metal
• In ionic bonding, metal atoms form cations
• In ionic bonding, non-metal atoms form anions
• Ions have full outer shells of electrons
• Metals are bonded to non-metals by an electro-static bond
• When oppositely charged ions are bonded by electrovalent bonds in the solid state, they are referred to as Ionic compounds
• Ionic compounds form a three dimensional structure called a crystal lattice
• covalent bonding occurs when two non-metals bond
• covalent bonding involves the sharing of valency electrons
• Molecules are formed by Covalent bonds
• Comparing Composition

  • Ionic Compounds - ions held together by strong ionic bonds
  • Covalent compounds - atoms held together by strong covalent bonds, molecules have weak van der waals forces
• Comparing State at Room Temp

  • Ionic compounds - crystalline solids, strong ionic bonds holding together lattice
  • Simple molecular compounds - liquids or gases, weak forces between molecules
• Comparing Melting and Boiling Points

  • Ionic Compounds - High, strong ionic bonds require a lot of energy to break
  • Simple Covalent Compounds - Low, weak intermolecular forces require little energy to break
• Comparing Solubility

  • Ionic Compounds - most soluble in water, insoluble in organic/covalent solvents
  • Covalent Compounds - most soluble in organic solvents e.g ethanol, insoluble in water
• Comparing Electrical Conductivity

  • Ionic Compounds - conduct electricity when molten or dissolved in water (ions are free to move)
  • Covalent Compounds - do not conduct electricity in any state (no free ions or electrons are present)
• metallic bonding occurs when two metals bonds
• In metallic bonding, the metal atoms are packed tightly in rows and the valency electrons from each atom are lost to a sea of electrons. These electrons are mobile and bind together the cations formed as a result of the atoms losing electrons
• Metals have the following properties as a result of their bonding:

  • solid at room temperature, except mercury
  • high melting and boiling points
  • conduct electricity (mobile electrons can move throughout the metal)
  • conduct heat (heat increases the kinetic energy of the mobile electrons, allowing heat to be passed through the metal)
  • malleable and ductile (layers of cations slip over each other whilst still being held together by the sea of electrons)
• Diamond lattice

  
• Graphite

  
• Sodium Chloride