topic c1- atomic structure + the periodic table

• neutron

  mass 1

  charge 0
• proton

  mass 1

  charge +1
• electron

  mass very small

  charge -1
• atoms

  • contain protons, neutrons and electron
  • are neutral, they have no overall charge
  • number of protons equals number of electrons
• atoms

  • atomic number and mass number describe an atom
  • the mass number tells you the total number of protons and neutrons in the atom
  • the nucleus has a radius of around 1 x 10 ^-14 m
• sodium

  23- mass number

  Na- element symbol

  11- atomic number

  • proton= 11
  • electrons= 11
  • neutrons= 12, 23-11=12
• elements

  • a substance made up of atoms that all have the same number of protons in their nucleus
  • consists of atoms with the same atomic number
  • atoms can be represented by symbols e.g.:
  • c= carbon
  • o= oxygen
  • mg= magnesium
  • pb= lead
• isotopes

  • different forms of the same element, which have the same number of protons, but a different number of neutrons
  • have the same atomic number but different mass numbers
• relative atomic mass

  sum of (isotope abundance x isotope mass number)

  /

  sum of abundances of all the isotopes
• compounds

  • two or more elements that are chemically combined
  • totally different properties from the properties of the original element
  • can be represented by formulas, example:
  • carbon + oxygen -> carbon dioxide
  • c + o2 -> co2
• chemical equations

  • chemical changes are shown by using chemical equations
  • methane burns in oxygen giving carbon dioxide and water:
  • methane + oxygen -> carbon dioxide + water
• symbol equations

  • show the atoms on both sides
  • reactants products
  • magnesium + oxygen -> magnesium oxide
  • 2mg + o2 -> 2mgo
  • need to be balanced
• mixtures

  • two or more elements that are not chemically combined
• chromatography

  1. draw a line in pencil at the bottom of the filter paper
  2. add a spot of ink on the line and place in the water
  3. make sure the ink isn't touching the solvent (water) otherwise it will dissolve
  4. place a lid on top of the beaker to stop it evaporating
  5. each dye in the ink will move up the paper at a different rate
  6. if the ink is insoluble it will stay on the baseline
  7. when the water has reached the end of the paper take it out
  8. the end pattern is called a chromatogram
• filtration

  • separates insoluble solids from liquids

  1. can be used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture
  2. it can be used in purification as well

  • insoluble means the solid can't be dissolved in the liquid
  • equipment for filtration:
  • filter paper
  • solid
  • liquid
  • funnel
  • beaker
  • filter
• evaporation

  1. pour the solution into an evaporating dish
  2. slowly heat the solution; this solvent will evaporate and the solution will become more concentrated
  3. keep heating the evaporating dish until you have dry crystals

  • soluble means the solid can be dissolved
  • equipment for evaporation:
  • evaporating dish
  • tripod
  • substances
  • safety mat
  • bunsen burner
• crystallisation

  1. pour the solution into a evaporating dish and gently heat the solution
  2. when some of the solvent has evaporated or when you see crystals remove the dish and leave the solution to cool
  3. the salt should start to form crystals- there should be salt crystallising out of the solution
  4. filter the crystals out of the solution and leave them in a warm place to dry
• simple distillation

  • can't separate liquids with similar boiling points, fractional distillation can
  • there should be a thermometer in a beaker, where the liquid is heated at the bottom
  • the part with the lowest boiling point evaporates first
  • the water goes into a condenser where the vapour is cooled and condensed
  • there are parts in the condenser the water can go out and come in
  • the water then travels into the beaker, where it is now a pure liquid
• fractional distillation

  • there is a boiling flask with a mixture of liquids in that is heated for evaporation
  • the liquids reach the top of the fractionating column when the temperature at the top matches their boiling point- this is checked with a thermometer at the top
  • the fractionating column is filled with glass rods
  • there is then a condenser that makes the liquids condense down
  • they then separate into different glass tubes, where the fractions are collected separately
• why did mendeleev leave gaps?

  put them in order of reactivity and was able to predict undiscovered elements
• mendeleev

  • put elements into groups of elements of similar reactions
  • left gaps
  • swapped elements- I + Te
  • + allowed him to make predictions
  • -still in order of mass
• history of the atom

  • john dalton described atoms as solid spheres
  • jj thompson proved this theory was wrong; he discovered electrons
  • he created the plum pudding model
  • ernest rutherford did the alpha particle scattering experiment- nucleus
  • niel bohr discovered that electrons orbit the nucleus around a fixed shell
• plum pudding model

  • positively charged
  • negative electrons
• magnesium

  • 2,8,2
  • nucleus in the middle
  • shells
  • electrons on shells
• history of the atom

  • jj thompson= he discovered electrons and came up with the plum pudding model
  • rutherford= discovered the nucleus and that most of an atom is space
  • chadwick= he discovered the neutron
  • bohr= he suggested that electrons could only orbit at a certain distance from the nucleus with a certain quantum of energy
• electronic structure

  • electrons occupy shells- sometimes called energy levels
  • electrons fill each shell up before occupying a new one, starting with the lowest energy
• shell- electrons allowed in each shell

  1 - 2

  2 - 8

  3 - 8
• electronic structure

  • lowest energy shells are closest to the nucleus
  • electronic structure can also be represented as number 2, 8, 1
• periodic table

  • the elements are placed in the periodic table in order of increasing atomic number (number of protons)
  • elements in the same group have the same number of electrons in their outer shell; they also have similar chemical properties
• noble gases

  • elements of group 0 are: helium, neon, argon, krypton, xenon, radon
  • all have stable electronic structures
  • the chemical properties of the elements in the periodic table repeat at regular (periodic) intervals
• the periodic table

  • mendeleev left gaps in his periodic table for undiscovered elements
  • in mendeleev's table of elements, the elements where grouped using their properties
  • before this atomic weight was used to order elements
  • elements in the same group have the same number of electrons in their outer shell
  • elements are now ordered by atomic number
• group numbers

  number of electrons in the outer shell
• period number

  number of shells with electrons in
• metals

  elements that can form positive ions when they react
• non-metals

  elements that don't form positive ions
• atoms

  tend to react to form full outer shells
• metals

  • get a full outer shell by losing electrons
  • more reactive when they lose electrons more easily
  • more reactive towards the bottom left of the periodic table
• non-metals

  • get a full outer shell by gaining or sharing electrons
  • more reactive when they gain electrons more easily
  • more reactive towards the top right of the periodic table
• transition metals

  • metals in the centre of the periodic table
  • properties:
  • multiple ions
  • form colourful compounds
  • good catalysts
• properties of metals (not true for every metal)

  • appearance- shiny
  • strength- strong but malleable
  • melting and boiling point- high
  • conductivity- good electrical and thermal conductors