How the Elements are Ordered

  • There are over 100 elements which have been isolated and identified.
  • Elements are arranged on the Periodic Table in order of increasing atomic number, where each element has one proton more than the element preceding it.
  • The table is arranged in vertical columns called Groups numbered 1 – 8 and in rows called Periods numbered 1 – 7.
    • Period: these are the horizontal rows that show the number of shells of electrons an atom has.
      • E.g: elements in Period 2 have two electron shells, elements in Period 3 have three electron shells.
    • Group: these are the vertical columns that show how many outer electrons each atom has.
      • E.g: Group 4 elements have atoms with 4 electrons in the outermost shell, Group 6 elements have atoms with 6 electrons in the outermost shell.

The-Periodic-Table-of-the-Elements, IGCSE & GCSE Chemistry revision notes

The Periodic Table

Predicting Reactions

  • The Group number of an element which is given on the Periodic Table indicates the number of electrons in the outer shell (valence electrons).
  • This rule holds true for all elements except helium, which although is in Group VIII, it has only one shell, the first and innermost shell which holds only 2 electrons.
  • We can use the Group number to predict how elements will react as the number of valence shell electrons in an element influences how the element reacts.
  • Therefore elements in the same Group react similarly.
  • By observing the reaction of one element from a Group you can therefore predict how the other elements in that Group will react.
  • By reacting two or more elements from the same Group and observing what happens in those reactions you can make predictions about reactivity and establish trends in reactivity in that Group.
  • For example, both lithium and sodium are in Group 1 and can react with elements in Group 7 to form an ionic compound (charges of Group 1 ions are +1, charges of Group 7 ions are -1).
  • The Group I metals become more reactive as you move down the Group while the Group VII metals show a decrease in reactivity moving down.

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.