chemistry- periodic table

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  • Created by: eleanor
  • Created on: 16-04-13 16:23

the early periodic table

  • Scientists didn't know about atomic structure so they based the first table on atomic weight. 
  • In 1863 Newland proposed a law of octaves, which stated that similar properties are repeated every eighth element.
    • He put the 62 elements known at that time into seven groups according to atomic weight. 
    • After calcium their properties didn't match as well within the groups
  • This meant other scientists rejected this theory 
  • In 1869 Mendeleev produced a better table, where he left gaps for undiscovered elements
  • He then tried to predict the properties of undiscovered elements and was right
  • After this many scientist accepted his idea. 
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the modern periodic table

  • Scientist found out about protons and electrons at the start of the 20th century. 
  • Soon after they developed models of the arrangements of electrons in atoms. 
  • The atomic number of an element determines its position in the periodic table. 
  • The number of electrons in the outer shell determines the properties
  • The group number equals the number of electrons on the outer shell
  • As the atom gets larger the less strongly attached to the nucleus 
    • when metals react they lose electrons, so the reactivity of the metals in a group increases going down a group 
    • when non metals react the gain electrons,so the reactivity of non-metals decreases down a group. 
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group 1- alkali metals

    • these metals react with air and water 
    • they are soft solids at room temperature 
    • they have a low melting point and a boiling point that decreases down the group 
    • the have low densities 
  • they react with water to produce hydrogen gas and a metal hydroxide that is an alkali 
  • they all have one electron in the outer shell they lose this electron in reactions to form an ionic compound in which they become positive -the react with halogens (group 7) 
  • they dissolve in water forming solutions that are colourless
  • the reactivity increases as you go down(
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transition element

  • the transition elements are found in the period table between group 2 and 3 
  • except for mercury,they have a higher melting and than the alkali metals
    • they are malleable and ductile and they are good conductor of heat and electricity 
    • they react only slowly or not at all, with oxygen and water.
    • they form positive ions 
    • they can be used as industrial catalyst 
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  • the halogens are non-metallic in group 7 of the periodic table 
  • they exist as small molecules made up of pair of atoms. they have low melting and boling points that increases godown the group. fluorine is a pale yellow gas 
    • cholorine is green gas 
    • bromine is a red-brown liquid 
    • iodine is a grey solid 
  • all of the halogens have seven electrons in their outer shell 
  • the reactivity of halogens decreases going down the group
  • a more reactivite halogenan displace a less reactive halogen from a solution of one of its salts.
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