Chemistry

• an atom is the smallest part of an element that can exist
• an element is a substance of only one type of atom
• what is a compound

  two or more elements chemically combined
• 5 methods to separate mixtures

  • Fractional/simple distillation
  • Crystallisation
  • Chromatography
  • filtration
• filtration is used to separate insoluble solids from a liquid
• what is a mixture 


  different elements not chemically combined
• describe 3 steps of filtration

  1. pour a mixture into funnel paper
  2. liquid passes through tiny pores of paper 3.solid can not pass through
• crystallisation is used to separate soluble solids from a mixture
• describe crystallisation

  we leave solution to evaporate for few days when water evaporates will leave behind crystals of solid mixtures
• how can we speed up crystallisation(downside)

  gently heat solution to evaporate however certain chemicals can break
• simple distillation is done to separate dissolved solid from a liquid
• describe process of simple distillation

  1. Heat solution 
  2. as we heat liquid it evaporates to vapour 
  3. Vapour passes past glass tube and thermometer reading increases
  4. Vapour passes into condenser turning back to a liquid as it passes through condenser 
  5. we’re left with crystals in flask and liquid in beaker 
• paper chromatography allows you substances based on their solubility
• describe 4 steps of chromatography

  1. take a piece of chromatography paper and draw a line near bottom 
  2. next put a dot of first colour and then a second dot of another colour
  3. place bottom of paper into solvent 
  4. solvent makes it up paper and dissolves ink in coloured dots 
• A pure compound in chromatography will produce a single spot in all solvents
• Starting line in chromatography is drawn with pencil as if we do it with pen ink could dissolve solvent and move up the paper 
• what the solid sphere theory 500 bc by Democritus

  every thing is made up of tiny particles which could not be divided and a separated by empty space
• what is the plum pudding model by JJ thomson

  a ball of positive charge with negative electrons scattered around
• what did jhon dalton say about solid spheres in 1803

  different types of spheres make up the elements
• rutherford realised most of the atom is empty space (1911)
• what’s the gold field experiment

  positive alpha particles charged at a thin sheet of gold
• what was the 3 conclusions from the gold field experiment

  • most alpha particles went straight through ( so most of the atom was empty space so plum pudding model is wrong ) 
  • some alpha particles were slightly deflected so nucleus must be charged deflecting positive alpha 
  • few alpha particles were deflected by >90 so the nucleus contained most of the mass 
• describe the nuclear model by Rutherford (1913)

  positive nucleus surrounded in the centre of the atom surrounded by a cloud of electrons
• what a criticism to the Rutherford model

  nothing stopping negatives electrons and positive nuclues from attracting and collapsing
• describe the 1913 Bohr final model of the atom

  positive nuclues in the centre surrounded by electrons on shells from a distance
• 20 years of the proton was discovered Chadwick provided evidence for the existence of a neutron
• what’s the mass for the subatomic structure

  • proton - 1
  • neutron- 1
  • electron-1/2000
• radius of atom is 1x10-10m and the radius of nucleus is 1x10-14m
• isotopes are atoms of an element with the same number of proton but a different number of neutrons
• Ions are charged atoms
• relative atomic mass is the weighted average of how common each isotope is
• atomic arrangement should be down in brackets
• periodic table is arranged in columns which we call groups
• • All elements with a group have similar chemical properties and react the same way as they all have same number of electrons on outer energy level 
• Dobereiner ordered elements with similar properties often occurred in 3s similar chemical properties called traids
• newland ordered electrons in increasing atomic weight saw that every 8th element reacted the same
• problems with new lands law of octaves 


  elements were grouped together when they had different properties
• Mendeleev developed the first periodic table
• Mendeleev ordered elements in order of increasing atomic weight
• 2 things Mendeleev did different

  • left space for undiscovered elements 
  • would switch elements so they fitted patterns of other elements in the same group