ch5 structure and properties of materials

• element

  • made up of 1 element
  • formed by natural occuring
  • has no consistuents
  • fixed melting and boiling point
• compound

  • 2 or more elements chemically combined
  • formed by chemical reaction
  • fixed ratio of consistuents
  • different properties from its consistuents
  • fixed melting and boiling point
• mixture

  • 2 or more elements and/or compounds not chemically combined
  • formed by physical mixing
  • has no fixed ratio of consistuents
  • properties similar to its consistuents
  • melting and boiling point over a range of temperatures
• atoms

  smallest particles of an element and have chemical properties same as its element
• molecules

  2 or more atoms chemically combined
• characteristics of atoms and molecules

  cannot be broken down as it is a pure substance
• elements are classified into

  • metals
  • non metals
  • metalloids ( have properties of both metal and non metal )
• what is an element?

  It is a pure substance that cannot be broken down into two or more simpler substances by chemical processes. e.g carbon, copper and oxygen
• Diatomic molecules

  are formed by the combination of two atoms.
• Polyatomic molecules

  formed by three or more atoms chemically combined together
• what is a compound?

  pure substance that contains two or more elements that are chemically combined in a fixed ratio.
• compounds have different properties from elements that form it


  e.g when magnesium (s) is burned, it combines with oxygen (g) in the air to form a compound called magnesium oxide (s)
• In thermal decomposition, heat is used to break down compounds into elements or simpler compounds. Or Electrolysis, where electricity is used to break down compounds into elements or simpler compounds.
• what are mixtures?

  made up of two or more substances that are not chemically combined.
• monoatomic

  singular atom
• components of a mixture can be separated by physical processes such as magnetic separation, filtration or distillation.
• No chemical reaction takes place when a mixture is formed hence usually there is little or no energy change.
• Ionic compounds form Giant Ionic Cystal Lattices with strong electrostatic forces of attraction and alternating +ve and -ve ions.
• Properties of Giant Ionic Crystal Lattice

  • High Melting and Boiling Point: a lot of energy required to overcome strong electrostatic forces of attraction
  • Solid at room temperature and pressure
  • Soluble in water
  • Conducts electricity in Molten/Aqueous state: structure is broken down and ions are mobile
• Affecting factor of Giant Ionic Crystal Lattice

  • the bigger the charges on the ions, the stronger the electrostatic forces of attraction thus melting and boiling point increase
• Covalent compounds form Simple molecular structures, Giant covalent substances and Macromolecules.
• Properties of Simple molecular structures

  • Low Melting and Boiling point; little energy required to overcome weak intermolecular forces
  • Cannot conduct electricity; except HCL which dissociates in water to form ions H+ and Cl-
  • Some are volatile; evaporate easily
  • Soluble in organic solvents
• Affecting factor of simple molecular structures

  • The larger the molecules, the stronger the intermolecular forces. Boiling and Melting point increase
• Giant Covalent Substances consist of two allotropes of carbon; Diamond and Graphite
• Properties of Diamond (strong covalent bonds) similar to silicon dioxide

  • Extremely high Melting and Boiling point; very large amount of energy required to overcome strong covalent bonds
  • Vey hard; a lot of energy required to break strong covalent bonds
  • Insoluble in both water and organic solvents
  • Cannot conduct electricity
• Applications of Diamond

  • drill bits or cutting tools
• Properties of Graphite

  • High Melting and Boiling point; a lot of energy required to overcome strong covalent bonds
  • Soft and slippery; weak intermolecular forces of attraction overcome easily, layers slide past one another
  • Insoluble in water and organic solvents
  • Can conduct electricity; has delocalised electron
• Applications of Graphite

  • conducting material in machinery
  • lubricant / pencil lead
• Macromolecules are many covalent molecules joined into chains
• Natural macromolecules

  • silk
  • wool
  • starch
  • rubber
• Man-made macromolecules

  • nylon
  • polystyrene
  • polyester
• Properties of macromolecules

  • Melt and Boil over a range of temperatures; molecules of different sizes soften over a range of temperatures when molecular vibrations produce high kinetic energy to overcome weak intermolecular forces
  • Cannot conduct electricity
  • Soluble in organic solvent, insoluble in water
• Metallic compounds form pure metals and alloys
• Properties of pure metals

  • High Melting and Boiling point; large amount of energy to overcome strong metallic bonds
  • good conductor of electricity and heat; delocalised electrons are mobile
  • insoluble in both water and organic solvents
  • soft, malleable and ductile; layers slide over eachother easily due to do regular arrangement
• Properties of Alloys

  • Melt and Boil over a range of temperatures; mixture made up of pure metal and other elements which all have different MP and BP
  • Good conductor or electricity and heat
  • Insoluble in water and organic solvents
  • Stronger, harder, less malleable, less ductile; large force required for layers to slide over one another due to irregular arrangement
• Solder (tin and lead) used as electrical wires or circuit board due to lower MP
• Steel (iron&carbon); used as cutlery, building and bridges due to its increased strength and hardness
• Stainless steel (iron,carbon,nickel,chromium) resist corrotion, used as surgical instruments