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A Simple Model of the Atom, Symbols, Relative Atomic Mass, Electronic Charge and Isotopes

1.1.1 Atoms, elements and compounds

Atom – smallest part of an element that can exist
Element
• Substance made of 1 type of atom
• Cannot be broken down chemically into simpler substance
Compound
• 2 or more elements chemically bonded in fixed properties
• Form / separate by chemical reactions
Molecules – collection of 2 or more atoms chemically bonded by covalent bonds

1.1.2 Mixtures

Mixture
• 2 or more elements / compounds not chemically bonded tgt
• Separated by physical processes
o Not involved chemical reactions
o No new substances made
Separation techniques

Simple distillation Separates a liquid from a solution
  1. Heat mixture until it boils & evaporates into water vapour
  2. Water vapour rises up & passes through condenser
  3. As condenser is cold, water vapour condenses back to water, which is collected in the flask
Fractional distillation Separates 2 liquids with similar boiling pt & are miscible
  1. Heat mixture
  2. Liquid with lower melting pt evapourates into vapour
  3. Vapour rises up & passes through fractionating column
  4. Vapour condenses back to water, which is collected in the flask
  5. Liquid with higher melting pt start evapourate
  6. Crude oil is heated & vaporised as it enters fractional distillation column
  7. Shorter chain lengths have weaker intermolecular forces & lower boiling pt
  8. This means they will condense at top of column where it’s cooler
  9. Longer chain lengths have stronger intermolecular forces & higher boiling pt
  10. This means they will condense at bottom of column where it’s hotter
  11. This is due to different chains length of hydrocarbons having different boiling pt so they can be separated & tapped off at different levels as fractions
Filtration Separates an insoluble solid from a liquid
  1. Pour solid and liquid mixture in filter funnel which contains filter papers
  2. Liquid goes through filer paper but solid does not
Crystallisation Separate soluble solid from solution
  1. Pour acid into beaker
  2. Gently heat acid with Bunsen Burner till almost boiling
  3. Add base to acid one spatula at a time & stir at the same time till base is in excess
  4. Filter excess base using filter paper & funnel
  5. Pour solution into evaporating basin
  6. Heat gently over beaker of boiling water till half of solution remains
  7. Leave to cool and crystallise
  8. Pat dry using filter paper
Chromatography Separate mixtures & give info to help identify substance
  1. Draw a pencil line on the paper.
  2. Place ink on the baseline in a dot.
  3. Place the paper into the beaker which has water in it. Make sure the baseline is above water level, so dye doesn’t dissolve in water.
  4. Hang paper over edge of beaker to keep it right.
  5. Put a lid on.
  6. Wait for solvent to go up paper near the top.
  7. Remove paper & let it dry.
  8. Draw circles around spots.

1.1.3  The development of the model of the atom

1. John Dalton – tiny hard sphere & indivisible

2. JJ Tomson – ‘Plum Puddy Model’

Experiment
•  Apply high voltages to gases at low pressure on beams of particles
Results
•  Attract on +ve charge
•  Show atom contains -ve charged particles (electrons)

  • -ve charged e– embedded in a cloud of +ve charge → atom is neutral
  • 3. Rutherford – ‘Alpha Particle Scattering Experiment’Experiment
    • Fired +ve alpha particle beams on extremely thin gold foil

    Results

    1. Straight through → most atom is empty spaced
    2. Slightly deflected → nucleus is +ve charged
    3. Deflected by >90° → nucleus is +ve charged
    • +ve nucleus concentrate mass of atom at centre of atom
    • -ve e– exist in cloud around nucleus
    • 4. Neil Bohr – ‘Nuclear Model’Experiment
      • Notice light given out when atoms were heated only had specific amount of energy

      Results

      • e- orbit nucleus in specific energy levels at specific distances with nothing in between
      • 5. James Chadwick – proved neutrons existed in nucleus in 1932
      • 1.1.4  Relative electrical charges of subatomic particles
      • 1.1.5 Size and mass of atoms
Name of particle Relative mass Electric charge
Proton 1 +1
Neutron 1 0
Electron -1

Why doesn’t an atom have charge?

  • Relative electrical charge
    • Electrons: -1, protons :+1
  • No of electrons = no of protons
  • Atom radius = 0.1nm (1 × 10-10m)
  • Nucleus radius =1/10000 of an atom (1 × 10-14m) 

    Formulae

    No of neutrons = mass no – atomic no = 23-11 = 12

    Atomic no = no of protons = 11

    Mass no = protons + neutrons

  • 1.1.6  Relative atomic mass

 

High relative atom mass

  • Less waste products
  • Less pollutants
  • 1.1.7  Electronic structure
  • Explain why fluorine and chlorine are in the same group of the period table. Give the electronic       structures of fluorine and chlorine in your explanation. (2)
  • Isotope is different forms of the same element, which have the same no of protons but different no of neutrons
  • The electronic structure of fluorine is 2,7 and chlorine is 2,8,7
  • F & Cl both has 7e- in outer shell

 

  • Isotope is different forms of the same element, which have the same no of protons but different no of neutrons
  • They both have 6 protons
  • 12C has 6 neutrons, 14C has 8 protons