C1.1 - The fundamental ideas in chemistry

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  • All substances are made up of atoms
  • Elements contain only one type of atom
  • Compounds contain more than one type of atom
  • Atoms are made of protons, neutrons and electrons
  • Protons have an charge of +1 and electrons have a charge of -1 but neutrons have no charge
  • Atomic number = number of protons (also number of electrons)
  • Mass number = number of protons + neutrons
  • The electrons in an atom are arranged in energy levels or shells
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The periodic table

  • Elements in the same group in the periodic table have the same number of electrons in their highest energy level and this gives them similar properties
  • The elements in Group 0 of the periodic table are called the noble gases. They're unreactive because their atoms have stable arrangements of electrons
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Chemical reactions

  • When elements react, their atoms join with other atoms to form compounds and this involves giving, taking or sharing electrons to form ions or molecules
    • Compounds formed from metals and non-metals consist of ions
    • Compounds formed from non-metals consist of molecules where the atoms are held together by covalent bonds
  • Chemical reactions can be represented by word equations or by symbol equations
  • No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants
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