1 - atomic structure + periodic table

• Atom


  The smallest part of an element that can exist
• Chemical symbol


  Representation of atoms of each element
• There are about 100 different elements (shown in the periodic table)
• Compound


  Formed from elements by chemical reactions (only separated into elements by chemical reactions)
• Chemical reaction


  Two or more elements chemically combined in fixed proportions (involve the formation of one or more new substances and a detectable energy change)
• Mixture


  Two or more elements or compounds (not chemically combined)
• The chemical properties of each substance in a mixture are unchanged
• Processes to separate mixtures

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Processes to separate mixtures

  • Physical processes which do not involve chemical reactions or new substances
• Plum pudding model


  The atom is a ball of positive charge with negative electrons embedded
• Nuclear model


  The mass of an atom was concentrated at the centre and that the nucleus was positively charged, and there was empty space
• Bohr model


  Electrons orbit the nucleus at specific distances
• Proton


  Positive charge (+1)
• Neutron


  Neutral charge (0)
• Electron


  Negative charge (-1)
• Number of electrons = protons in the nucleus (atoms have no overall electrical charge)
• Electron mass


  Very small
• Atom radius


  About 0.1 nm (1 x 10-10 m)
• Nucleus radius


  Less than 1/10 000 of the atom (about 1 x 10-14 m)
• Mass number


  Sum of the protons and neutrons
• Isotopes


  Different numbers of neutrons
• Relative atomic mass


  An average value that takes account of the abundance of the isotopes of the element
• Electronic structure


  The electrons in an atom occupy the lowest available energy levels (innermost available shells)
• The electronic structure of an atom can be represented by numbers or by a diagram
• Periodic table


  The elements are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups
• The table is called a periodic table because similar properties occur at regular intervals
• Elements in the same group

  Have the same number of electrons in their outer shell (outer electrons) and this gives them similar chemical properties
• Early periodic tables


  • Were incomplete and some elements were placed in inappropriate groups
• Mendeleev's periodic table


  • Left gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights
• The elements with the predicted properties were discovered and filled the gaps
• Isotopes explained why the order based on atomic weights was not always correct
• Metals


  React to form positive ions, left and bottom of the table
• Non-metals


  Do not form positive ions, right and top of the table
• The majority of elements are metals
• Group 0 (noble gases)

  • Unreactive
  • 8 electrons
  • Boiling point increases
  • Relative atomic mass increases (going down)
  • Do not easily form molecules because their atoms have stable arrangements of electrons (8)
• Group 1 (alkali metals)


  • React with oxygen, chlorine and water
  • 1 electron
  • Reactivity increases (going down)
• Group 7 (halogens)


  • Non-metals
  • Consist of molecules made of pairs of atoms
  • React with chlorine, bromine and iodine
  • A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
  • 7 elections
  • Reactivity decreases (going down)
  • Melting and boiling point increases