chemistry

• Atoms can gain or lose electrons to form ions.
• Isotopes are atoms with different numbers of neutrons but the same number of protons, resulting in different masses.
• The number of protons is equal to the atomic number.
• Cations have a positive charge, while anions have a negative charge.
• simple distillation is used to separate out a liquid from a solution
• simple distillation :

  1. the solution is heated
  2. the part of the solution with the lowest boiling point evaporates first
  3. vapour is then cooled, condenses and is collected
  4. rest of the solution is left behind in flask
• paper chromatography :

  1. draw a line near bottom of the paper in pencil
  2. add a spot of ink to line and place the sheet in a beaker
  3. place lid on top
  4. solvent will seep up carrying ink with it
  5. each different dye will form a spot in different places
  6. when solvent almost reaches top take it out to dry
  7. end result = pattern of spots called chromatogram
• fractional distillation is used to separate a mixture of liquids with different boiling points into two or more liquids
• fractional distillation :

  1. put mixture into flask and stick fractionating column on top then heat it
  2. liquid with lowest boiling point evaporates first
  3. when the temperature matches the boiling of this liquid it will reach the top of the column
  4. once the first liquid has been collected raise the temperature until the next one reaches the top
• group 0 - noble gases

  -they are unreactive

  -don't easily form molecules because their atoms have stable arrangements of electrons

  -8 electrons in their outer shell
• group 1 - alkali metals

  • single electron in outer shell
  • reactivity of elements increase going down the group
• All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced.

  lithium + water → lithium hydroxide + hydrogen
• When the alkali metals are cut, they initially appear shiny grey but quickly become dull and white as they react with oxygen in the air. This is known as tarnishing.
• lithium + oxygen → lithium oxide
• alkali metals properties :

  • they have low melting points
  • they are very soft and so can easily be cut with a knife
  • they have low densities
• group 7 - halogens

  • all have similar reactions becase of their 7 electrons in the outer shell
  • non metals
  • consist of molecules made of pair atoms
• In Group 7, the further down the group an element is the higher its relative molecular mass, melting point and boiling point.
• In Group 7, the reactivity of the elements decreases going down the group
• For ionic bonding the particles are oppositely charged ions.

  
  

  For covalent bonding the particles are atoms which share pairs of electrons.

  
  

  For metallic bonding the particles are atoms which share delocalised electrons.
• An ionic bond is the electrostatic force that holds ions together in an ionic compound. 
• 1. An ionic compound is a giant structure of ions.
  2. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.
  3. These forces act in all directions in the lattice and this is called ionic bonding.
• limitations of using dot and cross diagrams for ionic compounds: not always accurate due to it not showing the shape of the ionic compound
• limitations of using ball and stick diagrams to show a giant ionic lattice is that they're shown widely spread out when in reality the ions are packed together
• ball an d stick/space filling diagram limitation is that they only show a small part of the giant ionic lattice
• ionic compounds such as sodium chloride are arranged in a giant three-dimensional lattice structure, which is a regular repeating pattern of positive and negative ions. There are strong electrostatic forces of attraction that hold the oppositely charged ions together in the giant lattice.
• fullerenes are molecules of carbon atoms with hollow shapes
• fullerenes can be used as lubricants and catalysts
• graphite is formed from layers of carbon atoms in hexagonal rings
• in graphite each carbon atom has one free electron so it can conduct electricity
• graphene is a single layer of graphite and is one atom strong
• properties of graphene is

  • excellent conductor
  • strong
  • thin and lightweight
• properties of ionic compounds are

  • high melting/boiling point
  • when solid - can't conduct electricity
  • when melted - CAN conduct lectricity
• salt exam question model ; describe a method to make pure dry crystals of magnesium sulphate from a metal oxide and dilute acid

  • add sulphuric acid to beaker
  • warm gently
  • add MgO and sulphuric acid
  • stir
  • use filter paper to get rid of excess MgO
  • pour filtrate into evaporating basin
  • heat over bunsen burner
  • when crystals start to from remove from heat and leave to cool
• a polymer is a repeating units of monomers joined together by covalent bonds
• polymers are solid at room temperature because lots of energy is needed to break them
• polymers have low boiling points because they have weak intermolecular forces
• acid + base --> salt + water

  ( neutralisation)
• acid + metal oxide --> salt + water
• acid + metal hydroxide --> salt + water
• acid + metal carbonate --> salt + water + carbon dioxide