topic 2 - bonding, structure and properties of matter

• Solids have a fixed shape and cannot flow or be compressed
• Liquids flow and take the shape of their container but cannot be compressed
• Gases flow and completely fill their container and can be compressed
• The change from a solid to liquid is melting
• The change from a liquid to solid is called freezing
• The change from a liquid to gas is evaporation
• The change from a gas to liquid is condensation
• The change from a solid to gas is sublimation
• Energy is transferred from a substance to the surroundings when it condenses or freezes
• Energy is transferred from the surrounding to a substance when it melts, boils, evaporates, or sublimes
• An ion is an atom or group of atoms with a positive or negative charge
• Ions form when atoms lose or gain electrons
• If an atom loses an electron, it becomes a positive ion (+1)
• If an atom gains an electron, it becomes a negative ion (-1)
• Oppositely charged ions are strongly attracted to each other
• Ionic bonding is between a metal and non metal
• Ionic compound have high melting and boiling points due to extremely strong bonds. They are solid at room temperature
• ionic compounds do not conduct electricity as the ions are all locked in place in the giant lattice structure
• An ionic lattice is held together by strong electrostatic forces of attraction between the oppositely charged ions
• An ionic compound can conduct electricity when it has melted or is dissolved in water as the ions are free to move
• A covalent bond is formed when two atoms share a pair of electrons.
• One advantage of using dot and cross diagrams is that it shows which atom/s the shared electrons have come from
• One disadvantage of using dot and cross diagrams is that they don’t show how the atoms are arranged in space
• A substance with small molecules has strong covalent bonds but weak forces between individual molecules
• Most substances with simple molecules have low melting and boiling points
• Small molecules cannot conduct electricity as they have no charged particles that are free to move from place to place
• Most covalently bonded substances consist of small molecules which are two or more atoms joined by covalent bonds
• Giant covalent substances contain many atoms joined by covalent bonds
• Substances with giant covalent structures are solids at room temperature with very high melting and boiling points
• Most substances with giant covalent structures have no charged particles that are free to move
• Diamond and graphite are both forms of the atom carbon
• Diamond is a giant covalent structure

  . Each of its carbon atoms is strongly covalently bonded to 4 other carbon atoms

  . There are no free electron

  . The carbon atoms form a regular tetrahedral network structure
• Diamond is

  . Very hard

  . Has a high melting point

  . Is not conductive

  It can be used for

  . Cutting tools

  (oil rig drills, diamond tipped glass cutters)
• Graphite is a giant covalent structure

  . Each carbon atom forms 3 covalent bonds with other carbon atoms

  . The carbon atoms form layers of hexagonal rings

  . There are no covalent bonds between the layers

  . There is one delocalised electron from every atom
• Graphite is

  . A good conductor

  . Slippery (layers can slide over each other as there are weak forces between them)

  It can be used for

  . A lubricant

  . Electrodes in batteries and for electrolysis
• Graphene and fullerenes are forms of carbon
• Graphene is a single layer of graphite. It has a high melting point and is very strong. It conducts electricity well due to its delocalised electrons
• Graphene is useful in electronics and for making composites
• Fullerenes are molecules of carbon atoms with hollow shapes
• Buckminsterfullerene is a fullerene. It is a hollow sphere with 60 covalently bonded carbon atoms.