5.1 atomic structure and the periodic table

• chemical reactions always involve the formation of one or more new substances, and often involve an energy change
• compounds contain two or more different elements chemically combined in fixed proportions
• compounds can only be separated into elements by chemical reactions
• a mixture consists of two or more elements or compounds not chemically combined.
• the chemical properties of each substance in a mixture are unchanged
• alpha particle scattering experiment


  concluded that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
• niels bohr


  suggested that electrons orbit the nucleus at specific distances
• james chadwick


  proved that neutrons existed within the nucleus
• jj thomson


  discovered electrons, plum pudding model
• atomic number


  the number of protons in an atom of an element (bottom number)
• mass number


  sum of the protons and neutrons in an atom (top number)
• relative atomic mass


  an average value that takes account of the abundance of the isotopes of an element
• john newlands


  ordered his table in order of atomic weight
• dmitri mendeleev 


  ordered his table in order of atomic mass, left gaps for elements that he thought had not been discovered yet
• metals


  elements that react to form positive ions
• non-metals


  elements that do not form positive ions
• alkali metal + water -> metal hydroxide + hydrogen
• alkali metals react with oxygen to create an oxide
• alkali metals properties 


  low melting points, soft, low density
• alkali metals react with water to form metal hydroxides (which are alkaline) and hydrogen
• the reactivity of group one elements increases going down the group
• alkali metal + halogen -> alkali metal halides
• lithium + oxygen = red flame

  lithium + water = steady fizzing

  lithium + chlorine = white powder produced
• sodium + oxygen = orange flame, white solid

  sodium + water = rapid fizzing, melts into a ball

  sodium + chlorine = yellow flame, clouds of white powder
• potassium + oxygen = lilac flame

  potassium + water = sparks and lilac flame

  potassium + chlorine = vigorous, lilac flame
• noble gases (group 0)

  unreactive, low boiling point, low density
• halogens (group 7)


  diatomic molecules, melting and boiling points increase down group
• halogens react with metals to form ionic compounds
• halogens react with non metals to form covalent compounds
• a more reactive halogen can displace a less reactive halogen from solutions of its salts