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• protons have a relative mass of 1 and a charge of +1
• neutrons have a relative mass of 1 and a charge of 0
• electrons have a relative mass of very small and a charge of -1
• Nucleus:

  • in the middle of an atom
  • contains protons and neutrons
  • overall positive charge
  • mass of atom concentrated in the nucleus
• the number of protons in an atom is equal to the number of electrons
• element

  A) name

  B) atomic number

  C) symbol

  D) atomic mass

  
• the atomic number tells you how many protons are in an element
• the atomic mass tells you the total number of protons and neutrons in an atom
• when elements react, atoms combine with other atoms to form compounds
• compounds are substances formed from 2 or more elements, and the atoms are in fixed proportions and are held together through chemical bonds
• making bonds/compounds involved the atoms giving away, sharing or taking electrons. Only electrons are involved, no protons or neutrons
• a compound is formed from a metal and non metal consist of ions
• in a compound, the metal atoms lose electrons to form positive ions
• in a compound, non-metal atoms gain electrons to form negative ions
• the opposite charges of ions means they are strongly attracted to each other, this is called ionic bonding
• ionic bonding - metal and non-metal
• covalent bonding - non-metal and non-metal
• metallic bonding - metal and metal
• in a mixture, there are no chemical bonds and they can be easily separated
• separation techniques:

  • filtration
  • evaporation
  • crystallization
  • distillation
• filtration separated insoluble solids from liquids
• evaporation:

  1. pour solution into evaporating dish
  2. slowly eat solution. Solvent will evaporate and the solution will become more concentrated
  3. eventually crystals will form
  4. keep heating the dish until all that is left is crystals
• crystallization:

  1. pour solution into evaporating dish and heat
  2. once the solvent has evaporated or crystals form, remove dish from heat and leave it to cool
  3. crystals should form as it becomes insoluble in cold, high concentrated solution
  4. filter the crystals out and leave to dry
• if a solid can be dissolved, it is called soluble, there are 2 ways of separating a soluble solution:

  1. evaporation
  2. crystallization
• simple distillation is used for separating a liquid from a solution
• simple distillation:

  1. solution is heated, lowest boiling point starts to evaporate
  2. the vapor is cooled, condenses and is collected
  3. the rest of the solution is left in the tank
• filtration

  
• evaporation

  
• crystallization

  
• simple distillation

  
• if you have mixture of liquids to separate, then you use fractional distillation
• fractional distillation:

  1. put mixture in a flask with a fractionating column on top then heat
  2. the different liquids will have different boiling points - so evaporate at different temperatures
  3. the lowest boiling point will evaporate first - will condense as it reaches the top
  4. when the first liquid has been collected, you raise temp and repeat
• history of the atom:

  1806 - John Dalton described atoms as solid spheres and different spheres make up different elements
• history of the atom:

  in 1897, JJ thomson concluded atoms werent solid spheres. He measured charge and mass and concluded atoms contain smaller, negatively charged particles - electrons. This was called the plum pudding model
• John Dalton's atomic model

  
• JJ Thomsons atomic model

  
• history of the atom:

  the plum pudding model showed that the atom was a ball of positive charge with electrons stuck in it
• history of the atom:

  in 1909, Ernest Rutherford conducted the famous alpha particle scattering experiment - fired positively charged alpha particles at a sheet of gold
• history of the atom:

  from the plum pudding model, Rutherford was expecting the particles t pass straight through the sheet, or be slightly deflected at most. Most did go through but many more were deflected than expected, so the plum puddling model couldn't be correct
• history of the atom:

  to explain the results of his alpha particle experiment, Rutherford came up with the nuclear model. contained a tiny, positively charged nucleus, and a cloud of negative electrons surrounding it - so mostly empty space