bonding, structure and the properties of matter

Chemical Bonds

  • compounds = substance in which two or more elements are chemically bonded

  • ionic = particles are oppositely charged ions; electrostatic force of attraction between metals and non-metals

  • metallic = particles are atoms which share delocalised electrons; occurs in metallic elements and alloys

Ionic Bonding

  • metal + non-metal: electrons in the outer shell of the metal atom are transferred

    • metal atoms lose electrons to become positively charged ions

    • non-metal atoms gain electrons to become negatively charged ions

    • ion = an atom that has lost or gained electrons

  • ions produced by metals in groups 1 & 2 and ions produced by non-metals in groups 6 & 7 gain full outer shells of electrons so they have the same electronic structure as a group 0 element

Ionic Compounds

  • a giant structure of ions

  • held together by strong electrostatic forces of attraction between oppositely charged ions

  • since the structure is 3D, the forces act in every direction

eg. sodium chloride

Properties

  • ionic compounds have regular structures (giant ionic lattice) in which there are strong electrostatic forces between oppositely charged ions

    • they have high MP and BP as a lot of energy is required to break the numerous strong bonds

    • when melted or dissolved in water, ionic compounds conduct electricity as the ions are charged and free to move so they can carry a current - but they can’t when solid because the ions are fixed

Covalent Bonding

  • when atoms share one or more pairs of electrons

Covalent Structures

  • small molecules, such as HCl, H2, O2, Cl2, NH3 have strong covalent bonds within their molecules

    • Properties: usually gases or liquids with low MP and BP; weak intermolecular forces (increase with size of molecules as they have higher MP and BP); don’t conduct electricity as they don’t have a charge

  • polymers are large covalently bonded molecules

    • Properties: have very large molecules; atoms are linked to other by strong covalent bonds; solid at room temp as intermolecular forces are relatively strong

  • giant covalent structures (macromolecules) consist of many atom covalently bonded in a lattice structure

    eg. diamond, graphite and silicon dioxide

    • Properties: solids with very high MP; all atoms are linked to others by strong covalent bonds which must be overcome to melt or boil the substance

Metallic Bonding

  • the bonding in a metal consists of positive ions and delocalised electrons arranged in a regular pattern

  • the delocalised electron system consists of the electrons ‘lost’ from the atoms to form positive ions

  • delocalised electrons are free to move through the structure

  • the delocalised electrons are shared through the structure so metallic bonds are strong

Metallic Structures

  • metals have giant structures of atoms with strong metallic bonding

    • Properties: most metals have high BP and MP; arranged in layers which can slide over each other so metals are malleable which make them less useful for certain things

  • alloys are made from 2 or more different types of metals

    • the different sized atoms distort the layers in the structure so they can’t slide over each other making them harder than pure metal

  • metal conductors

    • good conductors as delocalised electrons carry electrical charge through the metal

    • good conductors of thermal energy because energy is transferred by delocalised electrons

The Three States of Matter

  • solid, liquid and gas

  • melting and freezing take place at FP

  • boiling and condensing take place at the BP

  • particle theory can help to explain melting, boiling, freezing and condensing

    • the amount of energy needed to change state from solid to liquid and liquid to gas depends on the strength of the forces between the particles

    • the nature of the particles involved depends on the type bonding and the structure of the substance

    • the stronger the forces between particles, the higher the melting and boiling point of the substance

  • limitations of the particle model include the lack of forces and that all particles are represented as spheres

Structure and Bonding of Carbon

Diamond

  • in diamond each carbon is joined to 4 other carbons covalently

    • it’s very hard, has a high MP and does not conduct electricity

Graphite

  • in graphite each carbon is covalently bonded to 3 other carbons forming layers of hexagonal rings which have no covalent bonds between the layers

    • the layers can slide over each other due to weak intermolecular forces and no covalent bonds between layers so graphite is soft and slippery

  • one electron from carbon is delocalised

    • can conduct electricity because the delocalised electron can move

Graphene and Fullerenes

  • graphene = single layer of graphite

    • has properties that make it useful in electronics and composites

    • very strong because atoms within layers are strongly bonded and elastic because planes of atoms can flex easily without breaking apart

  • fullerenes = molecules of carbon atoms with hollow shapes (nanoparticles)

    • based on hexagonal rings of carbon atoms but may also contain ring with five or seven carbon atoms

    • first fullerene to be discovered was the Buckminsterfullerene - C60 - which is spherical

  • carbon nanotubes = cylindrical fullerenes

    • high length to diameter ratio

    • properties make them useful for nanotechnology, electronics and materials

      eg. lubricants, delivering drugs to the body, catalysts, reinforcing materials such as tennis rackets

Nanoscience

Nanoparticles

  • 1 - 100 nanometres across

  • contain a few hundred atoms

    • smaller than fine particles which have diameters between 100 and 2500 nm

    • coarse particles (dust) have diameters between 1×10-5 m and 2.5×10-6 m

  • as size of cube decreases by a factor of 10, surface area to volume ratio increases by a factor of 10

  • nanoparticles have different properties to the “bulk” chemical it’s made from because of their high surface area to volume ratio; smaller quantities are needed to be effective than for materials with normal particle sizes

    eg. fullerenes have different properties to lumps of carbon

Uses of Nanoparticles

  • high surface area to volume ratio so good catalysts

  • highly selective sensors

  • stronger and lighter building materials

  • new cosmetics such as suncream and deodorant with no white marks

  • lubricant coatings for gears or artificial joints as they reduce friction

  • small electrical circuits for computers

  • potential disadvantages: concerns about nanoparticles being toxic as they may be able to enter the brain from the bloodstream and cause harm