AQA GCSE CHEMISTRY - Unit 1 (Core)

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C1 1.1 Atoms

  • All substances are made of atoms. A substance that is made of only one sort of atom is called an element. Elements are in the periodic table and the groups contain elements with similar properties. 
  • Atoms have a small nucleus in the centre, which is made up of protons and neutrons and around these are the electrons. 
    • Proton = +1 charge
    • Neutron = 0 charge 
    • Electron = -1 charge
  • In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge. 
  • The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number 
  • Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level. The electrons in an atom occupy the lowest available energy levels. 

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