atomic structure

• Atom


  Smallest part of an element that can exist
• Compounds


  2 or more element chemically bonded
• Mixture


  2 or more elements or compounds not chemically bonded together
• element

  substance made of one type of atom
• name four physical separation techniques

  • filtration
  • crystallisation
  • distillation
  • chromatography
• describe filtration

  • used to separate a insoluble solid from a liquid
  • pour the mixture through filter paper -
  • liquid passes through holes but the insoluble solid gets trapped behind as its too big
  • liquid is collected in a beaker
• describe crystallisation

  • used to separate a soluble solid from a liquid (suseptable to thermal decomposition)
  • heat the solution gently in a water bath
  • some of the solvent will evaporate and the solution will be more concentrated
  • when some crystals start to form remove from heat
  • as the solution cools more crystals will form
  • filter out these crystals and then leave them in a warm place to dry
• describe simple distillation

  • used to separate a liquid from a solution
  • heat the mixture so that a liquid we want evaporates
  • the vapour then travels down the condenser and is cooled and condensed to a liquid
  • this is collected in a beaker
  • doesnt work with mixtures of liquids with similar boiling points
• describe chromatography

  • can be used to separate different dyes in ink
  • draw a pencil line near the bottom of a piece of filter paper
  • add a spot of ink on the line and place in a beaker of solvent eg water
  • make sure the line is above the height of water
  • wait for the water to seep up the paper
  • the different substances will dissolve and be carried up the paper
  • they will travel at different rates and separate out
  • if any of the substances are insoluble they will stay on the baseline
• before the discovery of electrons , atoms were though to be what

  tiny undividable spheres
• the discovery of the electron led to which model of the atom

  plum pudding
• describe the plum pudding model

  • atom was a ball of positive charge
  • with negative electrons embedded randomly
• what 3 conclusions were made from the alpha scattering experiment


  • mass of the atom is concentrated in the centre
  • the nucleus is charged positively
  • mostly empty space
• describe the model which was developed after the alpha scattering experiment

  • the nuclear model
  • small positively charged nucleus
  • mostly empty space
  • negatively charged electrons floating around
• how did niels bohr adapt the nuclear model

  by suggesting that electrons orbit the nucleus at specific distances- added energy shells - prevent atom from collapsing
• which subatomic particle was discovered after energy shells

  protons - experiments proved the positive charge came from lots of smaller positively charged particles
• what did chadwick do and when

  about 20 years after the nucleus became an accepted scientific idea he proved the existence of neutrons within the nucleus
• relative charges of particles in an atom

  proton = +1

  neutron =0

  electron = -1
• why do atoms overall have no charge

  they have the same number of protons as electrons so the charges cancel each other out
• what is the atomic number

  number of protons in an atom
• relative mass of the parts of an atom

  proton =1

  neutron = 1

  electron = nearly 0
• what is the mass number

  neutrons + protons
• relative atomic mass

  an average value that takes account of the abundance of the isotopes of the element
• equation for relative atomic mass

  (relative atomic mass 1 x %)+(relative atomic mass 2 x %)/100
• what is an isotope

  atoms of the same element with a different number of neutrons but same number of protons
• distribution of mass in an atom

  almost all of the mass is in the nucleus
• radius of an atom and radius of a nuclei

  atom 1x10^-10

  nulcei 1x10^-14
• explain the structure of electrons

  electrons in an atom occupy the lowest available energy levels (innermost available shells)- 2 on the first- 8 on the second and thrid