OCR 21st century science C4 topic

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  • C4
    • What is an element?
      • Elements are substances that are only made with one atom
      • DIfferent elements have different proton numbers
      • They are arranged in order of increasing proton number in the periodic table
      • Relative Atomic Mass - is the total number of protons and neutrons in an atom
      • You can tell whether the element is a metal or a non metal by looking at their position in the table
    • Groups
      • A verticle column on the periodic table of elements is called a group
      • Elements in a group have similar properties
      • Group 1 for example includes elements like sodium and potassium
      • Group 1 elements have one electron in their outer shell
      • Group 7 elements have seven electrons in their outer shell
      • Group 1
        • There are 6 metals in group 1
        • They're called alkali metals
        • The properties of the metals alter as you go down the group
        • The further an element is down the group...
          • The higher the reactivity
          • the lower the melting and boiling points
          • the higher the density
        • Trends
          • Alkali metals have similar properties because they all have one electron in the outer shell
          • The alkali metals get more reactive because the outer shell is further away from the nucleus
      • Group 7
        • These are known as halogens
        • consists of 5 non metals
        • They can be used for bleach dyes and kill bacteria in water
        • The further down an element is down the group...
          • The lower the reactivity
          • the higher the melting and boiling points
          • The higher the density
        • They all have seven electrons in their outside of the group
    • Atoms
      • An atom has a small central nucleus, made up of protons and neutrons
      • The nucleus is surrounded by electrons which are arranged in shells
      • They have the same amount of protons as electrons
        • This makes the atom neutrally charged
      • A proton has the same mass as a neutron. This
      • To find out the amount of neutrons you subtract the bottom number from the top number
    • Balanced Equations
      • The total mass of the products of a chemical reaction = the total mass of the reactants
      • Chemical symbol equations must always be balanced
      • 2Na + 2H2O -> 2NaOH + H2
    • Ions
      • Ions are atoms that gain/lose atoms
      • atoms lose electron = positively charged
      • Atom gains electron = negatively charged
    • Ionic Bonding
      • Ionic bonding occurs between a metal and a non-metal
      • Compounds of group 1 and group 7 elements are called ionic compounds (salts)
      • When ionic crystals dissolve in water they conduct electricity

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