C1 - atomic structure

• What is an element

  • alL atoms are the same
• What is a compound

  • 2 or more elements
  • Chemically combined in fixed proportion
• What is fixed proportion

  Equal number of different elements
• what is a mixture

  • different elements or compounds not chemically combined
  • have to use physical separation techniques
• what is a molecule

  • elements chemically combined
  • Can be same or different elements
• What is a chemical formula

  tells us the elements in a molecule and number of atoms of each element
• What do physical separation techniques separate

  Mixtures
• key points of filtration

  • used to separate an insoluble solid from a pure liquid or solution
  • Involved a circle of filter paper folded into a filter funnel
  • The filtrate is the liquid which passes through the filter paper and the residue is the solid left
• example of filtration

  separate stone or sand grains from water or salt water
• how does filtration work

  • has tiny holes
  • the particles of the liquid, including dissolved solutes, passes through the holes
  • if the liquid contains an insoluble solid made of large particles, these larger particles cannot pass through
• when is crystallisation used

  • to produce solid crystals from a solution
  • When the solution is warmed some of the solvents evaporates leaving a more concentrated solution
• Steps of crystallisation

  1. solution is placed in evaporating basin and heated
  2. The volume of the solution decreases as the water has evaporated
  3. The particles form in the basin
  4. All water evaporates leavingg crystals
• when is simple distillation used

  • to separate a solvent from a solution
• simple distillation steps

  1. salt water is heated
  2. the water vapour cools in the condenser and drips into the beaker the water has condensed and salt remains
• how does simple distillation work

  • dissolved solute has a much higher boiling point than the solvent
  • When heated the solvent vapour evapourates
  • The gas is cooled and condenses
  • The remaining solution is more concentrated as amount of solvent decreases
• what is fractional distillation used for

  separate different liquids from a mixture
• steps of fractional distillation

  • different liquids have different boiling points
  • vapours rise through a column which is hot at the bottom and cold at the top
  • vapours condense when they reach a part of the column that is below the temperature of their boiling point
  • the liquid flow out of he column
• when were electrons discovered

  1897
• what did the discovery of electrons tell scientists

  • atoms are not tiny spheres that cannnot be divided
  • must have an internal structure
• what is the plum pudding model

  a ball of positive charge with negative electrons embedded in it
• what was the alpha scattering experiment

  1. scientists took gold foil (hammer into very thin foil, few atoms thick)
  2. fired positively charged alpha particles at the foil
  3. most alpha particles passed straight through the foil without changing direction
  4. some particles were deflected and changed direction
  5. some particles bounced off the gold foil
• what did the alpha scattering results show

  • told atoms are mainly empty space - most particles went through - plum pudding model was wrong
  • Because some deflected the centre of the atom is positive charge
  • because some bounce back the centre has great mass (nucleus)
• what is the nuclear model

  • mostly empty space
  • tiny positive nucleus in centre - most of the mass
  • negative electrons surrounding the atom
• What did Neil’s Bohr propose

  Electrons orbit the nucleus at specific distances rather than a general area
• what causes the positive charge in the nucleus

  Protons
• What did James Chadwick discover

  The nucleus also contains neutrons
• what is the radius of an atom

  0.2 nanometres / 1 x $10^{-10}$metres
• what is the radius of the nucleus

  1 x $10^{-14}$
• relative charge and mass of proton

  charge - +1

  mass - 1
• relative charge and mass of neutron

  charge - 0

  mass - 1
• relative charge and mass of electron

  charge - -1

  mass- very small
• which number is the atomic number

  bottom number
• what does the atomic number show

  number of protons
• How do you figure out the number of electrons

  Atomic number - same number of protons and electrons
• which number is the mass number

  top number
• what does the mass number show

  number of protons and neutrons
• how to work out number of neutrons

  mass number - atomic number
• what is an isotope

  an atom of an element with same number of protons but different number of neutrons
• common isotopes of carbon

  carbon 12 - 6 protons 6 neutrons

  carbon 13 - 6 protons 7 neutrons

  carbon 14 - 6 protons 8 neutrons
• what are ions

  atoms with an overall charge - have lost or gained an electron