bonding,structure and the properties of matter

• There are three types of strong chemical bonds: ionic, covalent and metallic.
• ionic bonding

  • metals and non-metals
  • particles are oppositely charged ions
• covalent bonds:

  • non-metals
  • particles are atoms which share pairs of electrons
• metallic bonds:

  • occurs in metallic elements and alloys
  • particles are atoms which share delocalised electrons.
• ionic bonding:

  • when atoms lose or gain electrons to form ions
  • outer shells are transferred
  • metals lose electrons to become positively charged ions
  • non-metals gain electrons to become negatively charged ions
• • ionic compounds is a giant structure of ions
  • held together by strong electrostatic bonds between oppositely charged ions
  • forces act in all directions in the lattice
• limitations of dot and cross diagrams:

  • only shows a few atoms when they actually form a giant ionic lattice which contains a large number of atoms arranged in a 3d arrangement
• limitations of ball and stick diagrams:

  • ions are not joined by sticks/ physical bonds. the oppositely charged ions are attracted by strong electrostatic forces of attraction
• limitations of two-dimensional diagrams:

  • giant ionic lattice are 3D, so the 2D diagrams only show 1 layer of it
• limitations of 3D diagrams :

  • only easily show ionic substances that exist in a 1:1 ratio as NaCl. difficult to show ionic substances such as Na2O
• • covalent bonding is when atoms share pairs of electrons
  • bonds between atoms are strong
  • consist of mainly small molecules
• Some covalently bonded substances have very large molecules, such as polymers.
• Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide
• Metals consist of giant structures of atoms arranged in a regular pattern.
• metallic bonding:

  • 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
• what are the three states of matter?

  solid, liquid and gas
• Melting and freezing take place at the melting point, boiling
• condensing take place at the boiling point.
• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance
• The nature of the particles involved depends on the type of bonding and the structure of the substance.
• The stronger the forces between the particles the higher the melting point and boiling point of the substance.
• Limitations of the simple model above include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid.
• in chemical equations:

  • solids are shown as (s)
  • liquids are shown as (l)
  • gases are shown as (g)
  • aqueous solutions are shown as (aq)
• properties of ionic compounds:

  • strong electrostatic forces of attraction in all directions between oppositely charged ions
  • high melting and boiling points because of large amounts of energy is needed to break the many strong bonds
  • conduct electricity when melted or dissolved in water because the ions are free to move and so charge can flow
• properties of small molecules:

  • usually gases or liquids
  • have low melting and boiling points
  • weak intermolecular forces are overcome when the substances melts or boils
  • intermolecular forces increase with the size of the molecules so larger molecules have higher melting and boiling points
  • do not conduct electricity because the molecules do not have an overall charge
• polymers:

  • very large molecules
  • atoms are linked by strong covalent bonds
  • strong intermolecular forces between polymer molecules so these substances are soild at room temperatures
• giant covalent structures:

  • solids with high melting points
  • strong covalent bonds which must be overcome to melt or boil these substances
  • eg: diamonds and silicon dioxide
• properties of metals and alloys :

  • giant structures of atoms with strong metallic bonding
  • high boiling and melting points
• pure metals:

  • atoms are arranges in layers which allows metals to be bent and shaped
  • too soft for many uses so are often mixed with other metals to make alloys which are harder
• alloys:

  • made up of atoms of different sizes
  • smaller or bigger atoms distort the layers of atoms in the pure metals
  • greater force is required for layers to slide over each other
  • making alloys harder
• metals:

  • good conductors of electricity
  • as delocalised electrons carry charge through the metal
  • good conductors of thermal energy
  • as energy is transferred by the delocalised electrons
• diamond:

  • each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure
  • is very hard
  • high melting point
  • does not conduct electricity as there are no free electrons
• graphite:

  • each carbon atom forms 3 covalent bonds
  • forms hexagonal rings which have no covalent bonds between the layers
  • one electron from each carbon atom is delocalised so is free to carry charge and conduct electricity
  • layers have weak forces so can slide over each other
• Graphene is a single layer of graphite
• properties of graphene:

  • strong covalent bonds between the carbon molecules
  • high melting point
  • strong
  • delocalised electrons that are free to move across the surface of graphene co can conduct electricity
• fullerenes:

  • molecules of carbon atoms with hollow shapes.
  • The structure of fullerenes is based on hexagonal rings of carbon atoms
  • may also contain rings with five or seven carbon atoms.
• The first fullerene to be discovered was Buckminsterfullerene (C60) which has a spherical shape.
• Carbon nanotubes are cylindrical fullerenes with very high length-to-diameter ratios. Their properties make them useful for nanotechnology, electronics and materials.
• Nanoparticles are smaller than fine particles (PM2.5), which have diameters between 100 and 2500 nm
• Coarse particles (PM10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust.