chem

• JJ. THOMSON had discovered ELECTRONS through experiments, leading to the "PLUM PUDDING MODEL", which showed the atom as a SPHERE of POSITIVE charge with ELECTRONS EMBEDDED within it.
• • ERNEST RUTHERFORD conducted the ALPHA PARTICLE SCATTERING experiment, which disproved the Plum Pudding model.
  • During this experiment, they fired ALPHA PARTICLES at a GOLD FOIL.
  • The gold foil was so thin, that they could assume that it was ONE ATOM THICK.
  • They observed that most alpha particles passed straight through the gold foil - mass concentrated in nucleus
  •  some were deflected - small positive charge
• • BOHR refined the nuclear model by introducing the idea that ELECTRONS ORBIT the nucleus in fixed SHELLS.
  • Bohr's model suggested that electrons could only occupy certain ENERGY LEVELS, at FIXED DISTANCES from the nucleus.
  • Bohr carried out further experiments which revealed the nucleus a whole number of smaller particles, each particle having the same amount of POSITIVE charge. These were called PROTONS.
• •  JAMES CHADWICK later discovered NEUTRONS, neutral particles in the nucleus, solidifying the nuclear model close to what is accepted today.
• Evaporation:

  • Pour the solution into an EVAPORATING DISH and gently heat it.
  • As the solvent evaporates, the solution becomes more concentrated, and eventually, dry crystals will form.
  • This method is best used when the substance DOES NOT DECOMPOSE upon heating.
• Crystallisation:

  • Similar to evaporation, start with a solution in an evaporating dish.
  • HEAT gently until crystals start to form, indicating that the solution has become saturated.
  • Allow the solution to COOL, which causes the formation of more crystals.
  • Filter out the crystals and leave them to DRY in a warm place.
• • SIMPLE DISTILLATION is a process to separate a LIQUID from a solution, often used when the liquids have different BOILING POINTS.
  • During distillation, the solution is heated to the temperature of the LOWEST BOILING POINT. This causes the component with the lower boiling point to EVAPORATE.
  • The vapour is then COOLED in a CONDENSER and collected as a liquid, leaving the component with the higher boiling point behind.
  • This method is ideal for purifying water from seawater or separating a liquid product from a reaction mixture.
• • Draw a line near the bottom of the filter paper with a pencil, as pencil marks are INSOLUBLE.
  • Place a spot of the substance to be separated on the line.
  • Use a suitable SOLVENT, such as water or ethanol, depending on the substances.
  • Ensure the spot does not touch the solvent when you place the filter paper in the beaker.
  • The solvent will move up the paper, taking the substances with it.
  • Different substances in the mixture will travel at different speeds, resulting in separate spots.
  • Once the solvent has nearly reached the top, remove the paper and let it dry to see the CHROMATOGRAM.
• • FRACTIONAL DISTILLATION is used for mixture of MORE THAN TWO liquids that have different bp.
  • It involves using a FRACTIONATING COLUMN. It creates a TEMPERATURE GRADIENT where the temperature is HIGH at the BOTTOM and LOW at the TOP.
  • As the vapour of the mixture rises, the temperature cools down which causes the components with HIGHER BOILING POINTS to CONDENSE. The component with the LOWEST BOILING POINT will rise and condense into liquid and get collected in the beaker.
  • process repeated, raising temperature gradually to collect other liquids at different bp
• groups - x

  periods - y
• If you INCREASE the H⁺ ION CONCENTRATION by a factor of 10 TIMES, the pH will DECREASE by 1.
• • The CONCENTRATION of an acid tells you the NUMBER OF ACID MOLECULES in a given volume.
  • The STRENGTH refers to the acid's degree of ionisation in water (how easily it breaks up into its ions
• acid + metal carbonae -> salt + water + carbon dioxide

  
• • BUCKMINSTERFULLERENE, is a SPHERICAL FULLERENE with a formula of C60.
  • Carbon nanotubes are CYLINDRICAL fullerenes with very HIGH length to diameter ratios.
  • They are good CONDUCTORS of HEAT and ELECTRICITY as they have DELOCALISED ELECTRONS, meaning they can be used in ELECTRONICS and nanotechnology.
  • They have a very high TENSILE STRENGTH without much MASS meaning they are useful for certain materials, such as the ones used in TENNIS RACKETS.
• Particle theory is useful for understanding how changes of state work, but just like the simple model, it has its limitations:

  • It assumes all particles to be SOLID, SPHERICAL and INELASTIC, when they aren’t.
  • It doesn’t consider the differences caused by different particles, such as atoms, ions and molecules.
  • It doesn't consider the INTERMOLECULAR forces between particles in different substances.

   
• • BELOW the MELTING POINT, a substance is SOLID.
  • ABOVE the BOILING POINT, it's a GAS.
  • BETWEEN these two points, it's a LIQUID.
• GROUP 1 ALKALI

  • The reactivity of these metals INCREASES as you go down the group. The outer electron is more easily lost due to the INCREASING DISTANCE from the nucleus and a WEAKER ATTRACTION.
  • They have LOWER MP AND BP
  • When they react, group 1 elements tend to form IONIC COMPOUNDS, these dissolve in water to create colourless ALKALI solutions
• GROUP 1 REACTIONS

  • When reacted with water, alkali metals produce hydrogen and react VIGOROUSLY.
  • The reactions become MORE VIOLENT reactions FURTHER DOWN the group.     
  • They also form HYDROXIDES that are alkaline when dissolved in water.
  • Group 1 metals react with Chlorine to form METAL CHLORIDES, which are WHITE SALTS.
  • The alkali metals react with Oxygen in the air forming METAL OXIDES, which is why the alkali metals TARNISH when exposed to the air. The metal oxide produces a dull coating which covers the surface of the metal.
• HALOGENS

  • These elements are DIATOMIC, meaning they exist naturally as molecules made of TWO ATOMS.
  • As you move DOWN GROUP 7. REACTIVITY DECREASES. It becomes more DIFFICULT for them to GAIN an extra electron because the number of SHELLS INCREASES and the atom gets BIGGER. There is LESS ATTRACTION between the NUCLEUS and the ELECTRON being gained making it MORE DIFFICULT to add it to its outer shell.
  • MP + BP INCREASE. The number of ELECTRONS in the molecules INCREASES down the group, the INTERMOLECULAR FORCES between them get STRONGER. This means MORE ENERGY is needed to break the bonds.

  
• GROUP 7 REACTIONS

  • When halogens react with NON-METALS, they form SIMPLE MOLECULAR compounds with COVALENT BONDS.
  • When halogens react with METALS, they form IONIC COMPOUNDS with IONIC BONDS.
  • HALOGENS undergo DISPLACEMENT REACTIONS where a MORE REACTIVE halogen REPLACES a LESS REACTIVE halogen in a compound.
• EVALUATION

  
• Strength of intermolecular forces

  Iodine atoms are LARGER as they are further down the periodic table.

  This means Iodine molecules have MORE ELECTRONS, meaning there are STRONGER INTERMOLECULAR forces between the molecules.

  MORE ENERGY is required to OVERCOME these forces which means Iodine has a HIGHER melting and boiling point than Chlorine
• PERCENTAGE MASS

  
• plum pudding vs nuclear

  • mostly empty space
  • mass concentrated in nucleus
  • positive charge all in nucleus
  • electrons and nucleus are separate
• no toxic chemicals to dispose of at the end of the cell's life

  take less time to refuel (than to recharge rechargeable cells)

  travel further before refuelling (than before recharging rechargeable cells)

  allow has a greater range

  no loss of efficiency (over time)

  allow does not lose capacity/range in

  cold weather 2
• electrostatic force of attraction btwn sea of electrons and metal ions
• 2H2 + O2 -> 2H2O
• The products formed cannot be reverted back into reactants in non-rechargeable batteries

  as the reaction is irreversible and the battery must be replaced (e.g. alkaline batteries)

  In rechargeable batteries the reactions are reversible and connecting the cells to an external electrical supply

  reverses the chemical reactions taking place.
• HYDROGEN FUEL CELL

  Advantages:

  They do not produce any pollution

  They produce more energy per kilogram

  No power is lost in transmission

  No batteries to dispose of which is better for the environment

  Continuous process and will keep producing energy as long as fuel is supplied

  Disadvantages:

  Materials used in producing fuel cells are expensive

  High pressure tanks are needed to store the oxygen and hydrogen in sufficient amounts which are dangerous and difficult to handle

  Fuel cells are affected by low temperatures, becoming less efficient

  Hydrogen is expensive to produce and store
• TITRATION

  use a pipette to add 25 ml of sodium hydroxide to a clean conical flask

  add a few drops of indicator and place the conical flask on a white tile

  fill the burette with sulphuric acid and record the starting volume

  slowly open the tap of the burette, and add the acid to the conical flask, swirling to mix

  stop adding the acid when the end-point is reached and

  record your final volume

  repeat steps 1-5 until you get concordant titres (results are within 0.10 ml of each other)

  Calculate mean titre and use this in concentration calculation.