C3 - structure and bonding

• What is covalent bonding?

  Bonding between 2 or more atoms where electrons are shared
• what is a molecule?

  a substance which contains two or more covalently bonded atoms
• what is a lone pair?

  a pair or electrons that are not part of the covalent bond
• Covalent bonding occurs between non-metals. Electrons are shared between the atoms so they they have a full outer shell.
• covalent bonds are strong and require a lot of energy to break. e.g. hydrogen: both hydrogen atoms have one electron in their outer shell. therefore both hydrogen atoms share one electron each, to give them both a full outer shell, we show this bond on a dot and cross diagram
• simple covalent compounds have low melting points and are often gases at room temperature e.g. oxygen and carbon dioxide. although the covalent bonds between the atoms are strong, the intermolecular forces between the molecules are weak. this means that only a small amount of energy is required to overcome these weak forces.
• what is an ionic bond?

  a bond formed by the electrostatic attraction of oppositely charged ion
• all atoms are more stable with a full outer shell of electrons

  some atoms will lose electrons to get a full outer shell - metals

  some atoms will gain electrons to get a full outer shell - non metals
• the group number indicates how many electrons an atom would have to lose or gain to get a full outer shell
• group 1:

  • lose 1
  • charge = +1
• group 2:

  • lose 2
  • charge - +2
• group 3:

  • lose 3
  • charge - +3
• group 5:

  • gain 3
  • charge - -3
• group 6:

  • gain 2
  • charge - -2
• group 7:

  • gain 1
  • charge - -1
• ionic compounds have regular structures - giant ionic lattices in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions
• ionic bonding:

  when a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred to the non metal atom. this means that the metal has a positive charge and the non metal has a negative charge. this means that an electrostatic attraction between the two ions, forms an ionic bond.
• models of ionic bonding-

  1. dot and cross diagrams - shows clearly how the electron are transferred - does not show 3D lattice structure
  2. 2D ball and stick model of ionic bonding - shows electrostatic forces between oppositely charged ions in an ionic compound - does not show 3D structure
  3. 3D ball and stick model of ionic bonding - clearly shows 3D structures of ionic lattice and how different ions interact with other ions in all directions to create an ionic lattice
• properties of ionic compounds:

  • high melting points - due to electrostatic forces between the oppositely charged ions - lots of energy required to break bonds
  • do not conduct electricity as a solid but do conduct electricity if they are dissolved in water or in liquid state - ions are free to move carrying the electric charge
• What is metallic bonding?

  A type of bonding which occurs only in metals
• what is an alloy?

  a mixture of 2 or more elements, one of which is a metal(the other may be metal or non metal)
• what is a delocalised electron?

  an electron that is not attached to an atom
• what does malleable mean ?

  the ability of a material to be bent into shape
• metallic bonding:

  metals form giant structures. the metal atoms form a regular pattern and donate their outer electron to the sea of delocalised electrons - free to move

  2D structure of metallic bonding:

  
• properties of metals:

  • good conductors of electricity - due to delocalised electrons which can carry the electric charge
  • good conductors of heat - free electrons can transfer the heat energy through the metal
  • malleable - layers of ions easily slide over one another - pure metals are too soft for uses such as buildings
• reactivity series:

  1. potassium K
  2. sodium Na
  3. lithium - Li
  4. calcium Ca
  5. magnesium Mg
  6. aluminum Al
  7. carbon C
  8. zinc Zn
  9. iron Fe
  10. Tin Sn
  11. Lead Pb
  12. Hydroegen H
  13. copper Cu
  14. silver Ag
  15. gold Au
• giant covalent compounds:

  all atoms are bonded to each other by strong covalent bonds.

  • high melting point because many strong covalent bonds need to be broken and this requires a lot of energy
  • three examples: diamond, graphite, silica
• diamond:each carbon is covalently bonded to 4 other carbonsproperties:

  • very hard
  • very high melting point due to strong covalent bonds
  • does not conduct electricity - no free electrons/ions

  
• graphite:

  each carbon is covalently bonded to 3 other carbons, there are weak bonds between the layers

  properties:

  • high melting point
  • conductor of electricity due to delocalised electrons which can carry a charge
  • slippery as layers can slide over each other

  
• silica:

  every silicon atom is bonded to 2 oxygen atoms and vice versa

  properties:

  • high melting point