atomic structure and the periodic table

• in an element all the atoms are the same
• there are 100 elements
• a compound contains two or more different elements chemically bonded in a fixed proportion
• in a compound the properties are different than the reactants used
• compounds are seperated using chemical techniques
• in a mixture diferent elements and compounds are not chemically combines retaining their own properties
• mixtures are seperated using physical techniques
• filtration is used to seperate an insoluble solid from a liquid
• in a filtration technique you need:

  • filtration paper
  • funnel
  • beaker
• crystallisation is used to seperate a soluble solid from a liquid
• crystallisation works by evaporating the liquid leaving the soluble solid in crystal form
• simple distillation is used when you want to keep the liquid seperated from a soluble solid
• simple distillation

  1. evaporate the liquid by heating in a flask
  2. condense the vapour in the glass tube using a condenser
  3. the liquid will collect is a beaker
• fractional distillation is sued to seperate a mixture of different liquids using a fractionating column
• atomic history:

  1. DALTON believes atoms were tiny spheres that cannot be divided
  2. electron was discovered
  3. THOMPSON created the plum pudding model
  4. RUTHERFORD alpha-scattering expermiments
  5. nuclear model
  6. BOHR - electrons orbit at specific distances
  7. CHADWICK- discovered protons and neutrons
• thompsons plum pudding model:

  • electrons in a sea of postitive charge
• alpha-scattering experiment:

  • bombarded alpha particles at a gold sheet
  • gold was used because it can be flattened to be a few atoms thick
  • alpha particles have a positive charge

  results:

  • most particles went straight through showing that most of the atom is emptey space
  • some were deflected showing that theres a positive charge at the centre
  • some bounced back showing that theres a concentrated mass (nucleus) at the centre
• nucleur model: before bohr

  • emptey space
  • positive nucleus
  • electrons are at the edge
• radius of an atom

  $0.1nm$
• radius of a nucleus

  $1\cdot10^{-14}m$
• atomic number is the number of protons

  mass number is the total protons and neutrons

  neutron= mass number - atomic number
• isotopes are the atoms of an element with a diferent number of neutrons
• all atoms and elements have the same number of protons
• ions are atoms which have a charge they have either gained or lost an electron
• all atoms and elements have the same number of protons
• calculating relative atomic mass of isosotopes:

  
  

  (mass no. of isotope 1 * %abundance isotope 1)

  +(mass no. of isotope 2 * %abundance isotope 2)

  
  

  /100
• • group number (column) tells you the amount of electrons in the valence shell
  • period (rows) tells the amount of shells
• the periodic table is displays similiar properties at regular intervals
• 1st version of the periodic table:

  • triads
  • lithium , sodium , pottasium
  • chlorine bromine iodine
• 2nd version of the periodic table newland:

  • law of octaves, every 8th element reacted similiarly
  • ! elements were grouped in different groups
• the modern periodic table:

  • ordered by atomic number
  • noble gases, they were not discovered by mendeleev yet
• development of the periodic table:

  triads

  newlands

  mendeleev
• group 0 (noble gases)

  • very unreactive
  • their valence shells are full
  • boiling point increases as you go down the group because mass number increases
• metals :

  • lose electrons
  • form positive ion
• group 1 (alkali metals)

  • 1 electron in its valence shell
  • soft and ductile
  • low density
  • highly reactive so stored in oil
  • reactivity increases as you go down the group
• alkali metal + oxygen = metaloxide

  alkali metal + water = metalhydroxide + hydrogen

  alkali metal + chlorine = metalchloride
• transition metals:

  • hard and strong
  • high melting point
  • high density
  • less reactive
  • form ions with different charges
  • form coloured compounds
  • used as catalysts
• group 7 - halogens

  • have 7 electrons on their valence shells
  • consists of two molecules joined by covalent bonds
  • as you go down molecules get bigger and the boiling point increases
  • as you go down reactivity decreases because influence from the nucleus is further away
  • reactive halogens displace less reactive halogens
  • halogen ions end in -ide
• 5 physical seperation techniques:

  • crystallisation
  • filtration
  • fractional distillation
  • distillation
  • chromatography
• mendeleev

  • ordered by increasing atomic weight (before the protons were discovered)
  • switched the order of elements if needed
  • left gaps and predicted their properties