Chem Aqa specification

• All substances are made of atoms , atoms are the smallest of an element that can exist
• Compounds are formed from elements by chemical reactions.
• Compounds contain two or more elements chemically combined in fixed proportions
• A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.
• Methods mixtures can be seperated

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography

  These physical processes do not involve chemical reactions and no new substances are made
• 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
• Atoms of the same element can have different numbers of neutrons , these atoms are called isotopes
• The relative atomic mass of an element is an average value that takes account of the number abundance of the isotopes of the element
• The elements in the periodic table are arranged in order of atomic (proton) number , so that elements with similar properties are in columns known as groups.