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
• Most substances are compounds
• A compound contains atoms of two or more elements, which are chemically combined 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 one molecule of the compound contains
• Compounds can only be separated into their component elements by chemical reactions or electrolysis