C2 - Bonding, structure, and the properties of matter

• Transition elements

  • Have ions with different charges
  • Form coloured compounds
  • Are useful as catalysts
• Chemists use theories of structure and bonding to explain the physical and chemical properties of materials
• Atoms can be arranged in a variety of ways, some of which are molecular while others are giant structures
• Theories of bonding explain how atoms are held together in these structures
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding

  Particles are oppositely charged ions
• Covalent bonding

  Particles are atoms which share pairs of electrons
• Metallic bonding

  Particles are atoms which share delocalised electrons
• Ionic bonding occurs in compounds formed from metals combined with non-metals
• Covalent bonding occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding occurs in metallic elements and alloys
• Electrostatic forces

  Explain chemical bonding
• Ionic bonding process

  1. Metal atom reacts with non-metal atom

  2. Electrons in outer shell transferred

  3. Metal atoms lose electrons

  4. Non-metal atoms gain electrons
• The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas
• The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram
• Dot and cross diagram example

  • Sodium chloride
• An ionic compound is a giant structure of ions
• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions
• These forces act in all directions in the lattice and this is called ionic bonding
• Ionic compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds
• When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow
• Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points
• These substances have only weak forces between the molecules (intermolecular forces)
• It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils
• The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
• These substances do not conduct electricity because the molecules do not have an overall electric charge
• The three states of matter are solid, liquid and gas
• Changes of state

  1. Melting and freezing at melting point

  2. Boiling and condensing at boiling point
• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance
• The stronger the forces between the particles the higher the melting point and boiling point of the substance
• Metals consist of giant structures of atoms arranged in a regular pattern
• The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure
• Metallic bonds

  Formed by the sharing of delocalised electrons
• When atoms share pairs of electrons, they form covalent bonds
• Covalently bonded substances may consist of small molecules
• Some covalently bonded substances have very large molecules, such as polymers
• Some covalently bonded substances have giant covalent structures, such as diamond
• Delocalised electrons

  Electrons that are free to move through the whole structure
• Metallic bonds

  Bonds formed by the sharing of delocalised electrons
• Students should be able to recognise substances as metallic giant structures from diagrams showing their bonding