Atomic Structure and the Periodic Table

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Atoms, Elements, Compounds and Mixtures

Atoms, Elements and Compounds:

  • All substances are made of atoms
  • An atom is the smallest part of an element that can exist
  • An element is a substance that contains only one sort of atom
  • There are about 100 different elements
  • Elements are displayed in the periodic table 
  • The atoms of each element are represented by a different chemical symbol, e.g. sodium = Na, carbon = C and iron = Fe
  • Most substances are compounds 
  • A compound contains atoms of two or more elements, which are chemically conbined in fixed proportions
  • Compounds are represented by a combination of numbers and chemical symbols called a 'chemical formula'.
  • Scientists use chemical formulae to show:
    • The different elements in a compound
    • How many atoms of each element on molecule of the compound contains
  • For example:
    • Water, H2O, contains 2 hydrogen atoms and 1 oxygen atom
    • Sulphuric acid, H2SO4, contains 2 hydrogen atoms, 1 sulfur atom and 4 oxygen atoms
  • Compounds can only be seperated into their


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