Chemistry- Topic 1

• Ion


  An ion is an ATOM that has LOST or GAINED ELECTRONS
• Elements


  Elements are substances made of ONE type of atom. Each atom of an element will have the same number of protons
• Isotopes


  Atoms with the SAME number of PROTONS but DIFFERENT numbers of NEUTRONS. They have the same atomic number but different mass numbers.
• Relative atomic mass


  The relative atomic mass is the AVERAGE MASS of all the atoms of an element, taking into account the different MASSES and ABUNDANCE
• What is abundance?


  The PERCENTAGE of atoms with a CERTAIN mass
• Formula for relative atomic mass

  (Mr x abundance of isotope 1 )+(Mr x abundance of isotope 2 ) / 100

  
• a substance consists of atoms which all have the same number of protons and electrons but different numbers of neutrons. Explain why this substance is an element.

  It's the number of PROTON in an atom that determines what TYPE of atom it is, so if all the atoms have the SAME NUMBER of PROTON then the substance is an ELEMENT.
• What is a compound?

  2 or more ELEMENTS CHEMICALLY COMBINED in fixed proportions
• What does a compound formed from a metal and a non-metal consist?

  It consists of IONS - the METAL atoms LOSE electrons to form POSITIVE ions and the NON-METAL atoms GAIN electrons to form NEGATIVE ions. The OPPOSITE charges of the ions mean that they're STRONGLY attracted to each other (ionic bonding)
• covalent bonding


  A COMPOUND formed from NON-METALS consists of molecules. Each atom SHARES an electron with another atom.
• Evaporation method


  1. Pour the solution into an EVAPORATING dish.

  2. Slowly HEAT the solution. The solvent will evaporate and the solution will get more concentrated. Eventually, CRYSTALS will start to form.

  3. Keep heating the evaporating dish until all you have left is dry crystals.
• Crystallisation method


  1. A solution is placed in an evaporating basin and HEATED with a Bunsen burner.

  2. The volume of the solution has DECREASED because some of the water has evaporated. SOLID particles begin to form in the basin.

  3. All the water has evaporated, leaving SOLID CRYSTALS behind.
• How to separate rock salt

  - GRIND mixture to make sure salt crystals are SMALL

  - put in WATER and stir, salt will DISSOLVE but sand won't

  - FILTER mixture. grains of sand collect in filter paper

  - EVAPORATE water from salt so it forms dry crystals
• Ammonia


  NH3
• sodium chloride


  NaCl
• carbon monoxide


  CO
• Calcium chloride


  CaCl2
• Sodium carbonate


  Na2CO3
• Sulfuric Acid


  H2SO4
• What is a physical method

  A method that DOESN'T involve a CHEMICAL reaction, so doesn't form any new substances
• Mixture


  A mixture consists of TWO or more substances (elements or compounds) that are NOT CHEMICALLY combined
• A mixture can be separated by physical processes such as

  Filtration

  Crystallisation

  Simple distillation

  Fractional distillation

  Chromatography
• Chromotography practical


  1)Draw a LINE near the bottom of a sheet of filter paper

  ( Use a pencil to do this- pencil marks are insoluble and won't dissolve in the solvent )

  2) Add a spot of the INK to the line and place the sheet in a beaker of solvent

  •The solvent used depends on what's being tested. Some compounds dissolve well in water, others in ethanol

  3) Make sure the ink isn't touching the solvent- you don't want it to dissolve into it.

  4) Place a lid on top of the container to stop the solvent evaporating

  5) The solvent seeps up the paper, carrying the ink with it

  6) EACH different DYE in the ink will move up the paper at a different RATE so the dyes will separate out. Each dye will form a spot in a different place (one spot per dye in the ink)

  7) If any of the dyes in the ink are INSOLUBLE (won't dissolve) in the solvent you've used, they'll stay in the BASELINE.

  8) When the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry.

  9) results- CHROMATOGRAM
• Chromatogram


  PATTERNS produced on chromatography paper
• When is simple distillation used?

  To SEPARATE a liquid from a solution
• Method of simple distillation 1

  - solution is HEATED in flask

  - the part of the solution that has the LOWEST boiling point evaporates first.

  - The vapour is then COOLED, CONDENSES and is COLLECTED

  -the rest of the solution is left behind in the flask (salt)
• Method of simple distillation 2

  1) solution is HEATED in flask

  2) it BOILS and STEAM rises into the condenser, salt is left behind

  3) the condenser is COLD (due to cold water jacket) so STEAM COOLS, CONDENSES and is COLLECTED as water

  4) water drips into the beaker, DISTILLED water (pure water without minerals)
• When is fractional distillation used?

  Fractional distillation is used to SEPARATE a mixture of liquids with DIFFERENT boiling points
• Method of fractional distillation

  1) Mixture is HEATED in a flask with a FRACTIONATING column on top, liquid with LOWEST bp evaporate first.

  When the temperature on the thermometer MATCHES the boiling point of this liquid, it will reach the TOP of the column.

  2) Liquids with HIGHER bp also start to evaporate but won't get all the way up the tube before CONDENSING.

  3) When liquid 1 has been collected you RAISE the temp until the next one reaches the top.
• Propan-1-ol, methanol and ethanol have boiling points of 97•C, 65•C and 78•C respectively. A student uses fractional distillation to separate a mixture of these compounds. State which liquid will be collected in the second fraction and explain why.

  ETHANOL. Ethanol has the SECOND lowest bp and will be collected once all the methanol has been dissolved off and the temperature INCREASED
• 1. John Dalton's Atomic Theory

  DALTON'S MODEL: thought of the atom as a SOLID SPHERE that could not divide into smaller parts
• 2. JJ Thompson's Plum Pudding model

  2)JJ THOMPSON- plum pudding model: The discovery of the ELECTRON led to the PLUM PUDDING MODEL. The plum pudding model suggested that the atom is a BALL/CLOUD of positive charge with electrons embedded in it).
• 3. Ernest Rutherford's Nuclear Model

  3) ERNEST RUTHERFORD'S- NUCLEAR MODEL: After the ALPHA PARTICLE SCATTERING experiment (fired alpha particles at thin GOLD foil), he , concluded that the MASS of at atom was concentrated at the CENTRE, in a CHARGED nucleus and most of the atom was EMPTY space. If the plum pudding were correct, then all the particles would go straight through, butsome BOUNCED back (hit nucleus), some were DEFLECTED (repelled by positive nucleus), and some went THROUGH (empty space)

  
  

  - PPM was replaced with NM and suggested that the electrons ORBIT the nucleus, but not at set distances
• Alpha scattering experiment


  Rutherford FIRED alpha particles at a piece of THIN GOLD foil.

  2) some of the alpha particles BOUNCED back and many were DEFLECTED

  3) this led to the conclusion that the POSITIVE charge and MASS of an atom is concentrated at the CENTRE (nucleus)
• 4. Bohr Model


  4. NIELS BOHR suggested that ELECTRONS orbit the nucleus at SPECIFIC DISTANCES. These orbits are called SHELLS/ ENERGY LEVELS. The theoretical calculations of Bohr agreed with experimental observations.
• 5. Further experiments- the proton

  5. Further experiments provided EVIDENCE that the nucleus can be divided into small particles called PROTONS
• 6. James Chadwick- the neutron


  JAMES CHADWICK: Proved the existence of NEUTRONS within the nucleus. This was 20 years after scientists had accepted that atoms have nuclei.
• History of the atom

  1) JOHN DALTON- Dalton's model: thought of the atom as a SOLID SPHERE that could not divide into smaller parts

  
  

  2) JJ THOMPSON- PLUM PUDDING MODEL: The discovery of the ELECTRON led to the plum pudding model (ball of positive charge with electrons embedded in it).

  
  

  3) ERNEST RUTHERFORD- NUCLEAR MODEL: After the ALPHA particle scattering experiment (fired ALPHA PARTICLES at thin GOLD foil), he, concluded that the MASS of at atom was concentrated at the CENTRE, in a CHARGED nucleus and most of the atom was EMPTY space. If the plum pudding were correct, then all the particles would go straight through, but some BOUNCED back (hit nucleus), some were DEFLECTED (repelled by positive nucleus), and some went THROUGH (empty space).

  
  

  NIELS BOHR: said ELECTRONS orbit nucleus at SPECIFIC DISTANCES

  
  

  Further experiments concluded: Positive charge of the nucleus could be divided into PROTONS

  
  

  JAMES CHADWICK: Proved the existence of NEUTRONS

  within the nucleus.
• Rutherford devised an experiment where ALPHA particles were FIRED through GOLD foil. Most of the particles PASSED through the foil, but some were DEFLECTED by different angles, and some were even deflected BACKWARDS. Explain why this disproves the plum pudding model


  If the plum pudding model was correct you would expect most of the alpha particles to have PASSED THROUGH the FOIL or only to have been DEFLECTED SLIGHTLY. The actual deflections of the particles suggests that atoms contain a SMALL NUCLEUS where the POSITIVE charge is concentrated
• why the new evidence from the scattering experiment led to a change in the atomic model

  The scientists realised that the POSITIVELY charged alpha particles were being REPELLED and DEFLECTED by a tiny concentration of POSITIVE charge in the CENTRE of the atom (the nucleus).