C2 chemical bonding -

• Chemical bonds - atoms can chemically bond in 3 ways:

  1. ionic bonding - involves the attraction between oppositely charged ions. They are found in compounds make of metals and non metals.
  2. covalent bonding - involves 2 atoms sharing 1 or more pairs of electrons. They are found in non metal elements and in compounds of non metals.
  3. metallic bonding - involves an attraction between positively charged ions and negatively charged, demoralised electrons. They are found in metals and alloys.
• Ions -

  • Charged particles.
  • Created when an atom or molecule gains or loses electrons.
  • Gaining electrons creates a negatively charged ion.
  • Losing electrons creates a positively charged ion.
• Positive ions (cations) -

  • Usually created when an atom or molecule loses electrons.
  • The metals in group 1 or 2 can easily lose electrons to become positively charged ions.
• Negative ions (anions) -

  • Usually created when an atom or molecule gains electrons.
  • The non metals in group 7 are most likely to gain electrons to fill up their electron shell and become negatively charged.
• Ions can be:

  • Single elements (e.g. F-).
  • A group of elements with an overall charge (e.g. SO4²-)
• Ionic bonding - when atoms form ions, they try to fill up or empty their outer electron shell. A metal atom transfers electrons to a non metal atom, allowing both of them to have a full outer shell.
• Group 1 ionic bonding -

  • Always lose an electron to form postive ions with a charge of +1.
• Group 2 ionic bonding -

  • Always lose 2 electrons to form doubly positive ions.
• Non metals group 6 and 7 -

  Always gain electrons to form negative ions.
• Noble gases group 0 -

  • Already have a full outer shell.
  • Unreactive
  • Don't normally form ionic bonds with other elements.
• Ionic compounds - form when millions of metal atoms transfer their outer electrons to millions of non metal atoms at the same time. The resulting oppositely charged ions are held together in ionic lattices.
• Ionic lattices - giant structures that are held together by strong electrostatic forces between oppositely charged ions.
• Electrostatic forces - are called ionic bonds and they extend in all directions within the lattice.
• Empirical formulae - you can work out the proportion of each ion in a compound. This is the simplest ratio of ions possible.
• Dot and cross diagrams - can show electrons being transferred and ions being formed. Dots represent electrons from 1 atom and crossses represent electrons from another atom.
• Colalent bonding - formed when 2 non metals share pairs of electrons. They are strong because the shared electrons are attracted to the nucleus of both atoms.
• Covalent bonded substances can be:

  • Small molecule like water.
  • Large molecules like polymers such as silk or polyester.
  • Giant colavent structures like diamond.
• Metallic bonding - are the electrostatic attractions between positive ions and negative delocalised electrons.
• Positive metallic ions -

  • Metals are made of giant structures of regularly arranged atoms.
  • The structure is a regular lattice of positive ions (cations) in a 'sea' of delocalised electrons.
• Delocalised electrons -

  • Not bound to an atoms and are free to move around with the lattice.
  • Happens because metal atoms have a small number of electrons in their outer shells. 
• Dot and cross diagrams can be used to represent covalent bonds and to show the sharing of electron pairs.

  • Chlorine (Cl2) - watch atom beings with 7 electrons in outer shell. They shair 1 pair of electrons in a single covalent bond, therefore each Cl atom obtains a full outer shell with 8 electrons.
  • Water (H2O) - oxygen had 6 electrons in outer shell, it needs 2 extra electrons. It forms a single bond with 2 hydrogen atoms.
  • Double and triple bonds - stronger, require more energy to break.
• There are 3 types of covalent bond:

  1. Single - 1 shared pair of electrons, like group 7, as each atom needs to gain 1 electron to have a full outer shell.
  2. Double - 2 shared Paris of electrons, like group 6, as each atom needs to gain 2 electrons to have a full outer shell.
  3. Triple - 3 shared pairs of electrons, like group 5, as each atom needs to gain 3 electrons to have a full outer shell.
• Representing covalent bonds -

  1. Dot and cross with shells
  2. Lines
  3. Ball and stick
  4. Dot and cross without shells
• States of matter -

  • Solid - particles very close together, vibrate in fixed positions. Fixed shape and volume
  • Liquid - particles close together but move around and flow randomly. Fixed volume but can change shape.
  • Gas - particles are far apart,ove randomly. Change shape and volume.
• Changing state - when particles gain or lose energy, due to heating or cooling, they overcome or submit to the forces of other particles. This causes them to change state.
• Heating - can cause a substance to melt or boil.

  • When a solid is heated to its melting point, it melts and becomes a liquid.
  • Boiling - when a liwuid is heated to its boiling point, it evaporates and becomes a gas.
• Cooling - can cause a substance to either condense or freeze.

  • Condensing - when a gas is cooled down to its boiling point, it condenses and beocmes a liquid.
  • Freezing - when a liquid is cooled to its melting point, it freezes and becomes a solid.
• Processes -

  • Melting - solid -> liquid
  • Boiling - liquid -> gas
  • Freezing - liquid -> solid
  • Condensing - gas -> liquid
  • Deposition - gas -> solid
• State symbols - letters that tell us what state of matter a substance is in. There are 4 types:

  • S = solid
  • L = pure liquids
  • Aq = aqueous, used more than L
  • G = gases
• Forces between particles - the amount of energy required for substances to change state depends on whether the forces between their particles are strong or weak.

  • Strong - more energy required, high melting and boiling points.
  • Weak - less energy required, low melting and boiling points.
• ionic compounds - form giant ionic lattice structures, which are held together by strong electrostatic forces between oppositely charged ions. These electrostatic forces are called ionic bonds.
• Properties of Ionic Compounds -

  • High melting and boiling points - lots of energy is needed to break the electrostatic forces between the ions and electrons.
  • Cannot conduct electricity when solid - ions are in a fixed place, meaning they cannot flow.
  • Can conduct electricity when liquid or in solution - ions are free to move, meaning charge can flow and electricity can be conducted.