2 - structure and bonding

• 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
• Chemical bonding can be explained in terms of electrostatic forces and the transfer or sharing of electrons
• Metal atom reacting with non-metal atom

  1. Electrons in the outer shell of the metal atom are transferred

  2. Metal atoms lose electrons to become positively charged ions

  3. Non-metal atoms gain electrons to become negatively charged ions
• 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 (Group 0)
• Ionic compound

  A giant structure of ions
• Ionic compounds

  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in all directions in the lattice
• Ionic bonding

  The strong electrostatic forces of attraction between oppositely charged ions in an ionic compound
• Covalent bond

  When atoms share pairs of electrons
• Covalent bonds

  • Strong
  • May consist of small molecules
  • May have very large molecules, such as polymers
  • May have giant covalent structures, such as diamond and silicon dioxide
• Metallic bond

  The sharing of delocalised electrons in a giant structure of metal atoms arranged in a regular pattern
• 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
  • The sharing of delocalised electrons gives rise to strong metallic bonds
• The three states of matter

  • Solid
  • Liquid
  • Gas
• Melting and freezing

  Take place at the melting point
• Boiling and condensing

  Take place at the boiling point
• Simple model

  Particles represented by small solid spheres
• Particle theory

  • Can help to explain melting, boiling, freezing and condensing
• Energy needed to change state

  Depends on the strength of the forces between the particles of the substance
• Nature of the particles

  Depends on the type of bonding and the structure of the substance
• Stronger forces between particles

  Higher melting point and boiling point of the substance
• Limitations of the simple model include that there are no forces, all particles are represented as spheres and the spheres are solid
• States of matter in chemical equations

  • (s) - solid
  • (l) - liquid
  • (g) - gas
  • (aq) - aqueous solution
• Ionic compounds

  • Have regular structures (giant ionic lattices)
  • Have strong electrostatic forces of attraction in all directions between oppositely charged ions
  • Have high melting points and high boiling points
  • Conduct electricity when melted or dissolved in water because the ions are free to move and so charge can flow
• Substances that consist of small molecules

  • Are usually gases or liquids
  • Have relatively low melting points and boiling points
  • Have only weak forces between the molecules (intermolecular forces)
  • Melt or boil by overcoming the intermolecular forces, not the covalent bonds
  • Have higher melting and boiling points as the size of the molecules increases
  • Do not conduct electricity because the molecules do not have an overall electric charge
• (s), (l) and (g)

  The three states of matter shown in chemical equations
• (aq)

  Aqueous solutions
• Ionic compounds

  • Have regular structures (giant ionic lattices)
  • Have strong electrostatic forces of attraction in all directions between oppositely charged ions
  • Have high melting points and high boiling points
  • Conduct electricity when melted or dissolved in water because the ions are free to move and so charge can flow
• Substances that consist of small molecules

  • Usually gases or liquids
  • Have relatively low melting points and boiling points
  • Have only weak forces between the molecules (intermolecular forces)
  • Intermolecular forces are overcome, not the covalent bonds, when the substance melts or boils
  • Do not conduct electricity because the molecules do not have an overall electric charge
• Intermolecular forces

  • Increase with the size of the molecules
  • Larger molecules have higher melting and boiling points
• Intermolecular forces are weak compared with covalent bonds to explain the bulk properties of molecular substances
• Polymers

  • Have very large molecules
  • The atoms in the polymer molecules are linked to other atoms by strong covalent bonds
  • The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature
• Substances that consist of giant covalent structures

  • Are solids with very high melting points
  • All of the atoms in these structures are linked to other atoms by strong covalent bonds
  • These bonds must be overcome to melt or boil these substances
• Giant covalent structures

  • Diamond
  • Graphite (forms of carbon)
  • Silicon dioxide (silica)
• Metals

  • Have giant structures of atoms with strong metallic bonding
  • Most metals have high melting and boiling points
  • In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped
  • Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder
• Alloys

  Harder than pure metals in terms of distortion of the layers of atoms in the structure of a pure metal