Paper 1

• Everything is made of atoms, it is the smallest part of an element
• Elements


  • There are about 200 different elements each with a symbol
  • Elements contain only one type of atom
• Compounds


  • Are formed by elements in chemical reactions
  • Are 2 or more elements that are chemically combined
• New experimental evidence may lead to the model of the atom being changed or replaced
• Early ideas about atoms

  • Before the discovery of the electron, atoms were just spheres, they couldn't be divided
  • After the electron was discovered, the atom became a ball of positive charge with negative electrons scattered in it
• Separation methods for mixtures

  • Crystallization
  • Filtration
  • Separating soluble and insoluble substances
  • Chromatography
  • Simple distillation
  • Separating solutions
  • Fractional distillation
• Alpha particle scattering showed that the nuclear mass of an atom was concentrated in the centre, and was charged to attract electrons at a distance
• James Chadwick provided evidence to show the existence of neutrons in the nucleus
• Relative charges


  • Proton: +1
  • Electron: -1
  • Neutron: 0
• Size and mass


  • Atoms are very small, radius is 0.1nm (1x10^-10m)
  • Mass is mainly in the nucleus
• Atomic number


  The proton number, it is different for every element
• Mass number


  The number of protons and neutrons in the nucleus
• Isotopes


  Atoms that have the same number of protons (element), but different numbers of neutrons
• Electronic configurations


  1. Electrons fill the lowest energy levels first

  2. This starts from the nucleus, following a set pattern up to the following maximum: 1st shell - 2 electrons, 2nd shell - 8 electrons, 3rd shell - 8 electrons, 4th shell - 2 electrons
• A pure substance can be a single element or a single compound
• A pure substance is not mixed with any other substance
• Determining if a substance is pure

  1. Measure its melting point and boiling point

  2. A pure substance melts and boils at specific fixed temperatures

  3. An impure substance melts and boils over a range of temperatures
• Pure substances


  • Pure silicon
  • Pure sodium chloride
• A formulation is a complex mixture that's been designed as a useful product
• In a formulation, the quantity of each component is carefully measured so that the product has the desired properties
• Paper chromatography


  A separation technique used by scientists to identify substances in a mixture based on their different solubilities
• Paper chromatography procedure


  1. Draw a pencil line near the bottom of chromatography paper

  2. Put a dot of the first color/substance on the pencil line

  3. Put a dot of the second color/substance next to the first

  4. Place the bottom of the paper into a solvent

  5. The solvent moves up the paper, dissolving and carrying the substances with it

  6. The substances separate based on their solubility, forming different spots on the paper
• Stationary phase and mobile phase

  • Stationary phase: the chromatography paper (does not move)
  • Mobile phase: the solvent (moves up the paper)
• Characteristics of pure substances and mixtures

  • A pure compound will produce a single spot in all solvents
  • Compounds in a mixture may separate into different spots depending on the solvent
• Using paper chromatography to identify an unknown substance

  1. Place a dot of the unknown substance on the pencil line

  2. Place the bottom of the paper into a solvent

  3. Measure the distance moved by the unknown substance and the solvent

  4. Calculate the RF value (distance moved by substance / distance moved by solvent)

  5. Look up the RF value in a database to identify the substance
• Paper chromatography


  A technique used to identify substances in a mixture
• Paper chromatography procedure


  1. Draw horizontal pencil line 2cm from bottom of paper

  2. Mark 5 equal spots across the line

  3. Use capillary tube to put small spots of known and unknown colors on the pencil spots

  4. Pour water into beaker to 1cm depth (solvent)

  5. Attach paper to glass rod and lower into beaker, ensuring paper edge is above water and paper doesn't touch sides

  6. Cover beaker with lid to reduce evaporation

  7. Remove paper when water has traveled 3/4 up, mark water line

  8. Hang paper up to dry
• Paper chromatography


  • Separates mixture into its components
  • Allows identification of unknown substances by comparing to known substances
• Rf value


  Ratio of distance moved by chemical to distance moved by solvent, used to identify chemicals
• Several chemicals could have the same Rf value, so further analysis may be needed
• If a chemical has not been analyzed before, its Rf value will not be in a database
• Hydrogen gas test


  Use a burning splint - hydrogen gas burns rapidly and produces a pop sound
• Oxygen gas test


  Use a glowing splint - the splint will relight or burst into flames in the presence of oxygen
• Carbon dioxide gas test

  Bubble the gas through limewater (calcium hydroxide solution) - the limewater will turn cloudy if carbon dioxide is present
• Chlorine gas test


  Insert damp litmus paper - chlorine gas will bleach the litmus paper and turn it white
• These gas tests are straightforward but it's important to learn them well as they could come up in exams and it's easy to confuse them
• Flame tests


  • Used to identify unknown compounds containing metal ions
  • Involve placing a small amount of the chemical on a wire and inserting it into a blue Bunsen burner flame
  • The color of the flame can be used to identify the metal ion present
• Metal ions identified by flame tests

  • Lithium (crimson flame)
  • Sodium (yellow flame)
  • Potassium (lilac flame)
  • Calcium (orange-red flame)
  • Copper (green flame)
• Flame tests have limitations - the color can be difficult to distinguish, especially with low concentrations or mixtures of metal ions
• Flame emission spectroscopy


  An instrumental technique where the sample is placed in a flame, the light given out is passed into a spectroscope, and the resulting line spectrum is used to identify the metal ion