What are the patterns in the properties of elements?

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  • Chemical patterns
    • Element
      • Relative atomic mass
        • Minus the proton number equals the neutron number
      • Proton number
        • Is also the electron number
        • Defines the element
    • Periodic Table
      • Elements are arranged in order of proton number
        • This gives a repeating pattern of their properties
          • Each element is placed beneath those with similar properties
      • Attempts were made to order the elements
        • Their actual masses could not be measured so they were compared to the mass or hydrogen
          • This is called RELATIVE ATOMIC MASS
      • Döbereiner proposed the 'law of Triads'
        • Three elements with similar properties
          • The relative atomic mass of the middle element was close to the average of the other two
      • Newlands arranged the elements in order of their atomic mass.
        • Proposed the 'law of Octaves'
          • Every eight element had similar properties
            • Didn't work for all elements so theory dismissed
      • Mendeleev put the elements in order of relative atomic mass and left gaps for unknown elements
        • He predicted what the properties of the undiscovered elements would have
        • Arranged it so that groups of elements with similar properties fell into vertical columns
      • Period
        • A row of elements, the row number tells you how many shells the atom will have
      • Column
        • Each column contains a group of elements with similar properties
          • The Group number tells you the amount of electrons in the outer shell
      • Metals and Non-metals
        • Metals on the left, non-metals on the right
      • Because there are patterns in the way the elements are arranged you can predict properties of elements
    • Alkali Metals
      • Li (Lithium)
      • Na (Sodium)
      • K (Potassium)
      • Shiny when freshly cut but tarnish rapidly ( they react with the oxygen)
      • Soft metals
      • Increased reactivity as you go down the group
      • Melting points and Boiling points decrease as you go down the group
      • The densities generally increase as you go down the group
      • All have similar formulaes of compounds
      • Reactions with cold water:
        • 2 Li + 2 H2O -> 2LiOH + H2
          • Produce strong alkaline solution and hydrogen gas
          • Fizzes steadily until it disappears
        • 2 Na + 2 H2O -> 2NaOH + H2
          • Produce strong alkaline solution and hydrogen gas
          • Fizzes quickly along the surface of the water. Burns with an orange flame
        • 2 K + 2 H2O -> 2KOH + H2
          • Sets on fire with a lilac flame. Fizzes around vigorously.
      • Reactions with chlorine:
        • 2 Li + Cl2 -> 2LiCl
          • Produce colourless, crystalline salts
          • White powder settles in jar
        • 2 Na + Cl2 -> 2NaCl
          • Produce colourless, crystalline salts
          • Burns with a yellow flame. Clouds of white powder is made
        • 2 K + Cl2 -> 2KCl
          • Reacts more violently than Sodium!
      • Because they are so reactive you must wear goggles and gloves. They will react with the water in your sweat!
    • Hazardous symbols
      • Explosive
        • Enough stored energy in them to explode
          • Illegal to carry out unauthorised experiments
      • Toxic
        • Poisonous chemicals
          • Wear goggles, gloves, mask and use in fume cupboard
      • Corrosive
        • Concentrated solutions of strong acids and strong alkalis
          • Wear goggles and gloves
      • Oxidizing
        • They provide oxygen to substances that are flammable
          • Wear eye protection and keep away from flammable things
      • Highly flammable
        • Chemicals that ignite very easily
          • Wear eye protection. Keep away from flames and sparks and also from oxidising agents.
    • Halogens
      • Cl2 (Chlorine)
        • Gas at room temperature
        • Yellow green
      • Br2 (Bromine)
        • Liquid at room temperature
        • Red-Brown
      • I2 (Iodine)
        • Solid at room temperature
        • Shiny purple crystals. Dark purple gas
      • Diatomic molecules
      • Melting and boiling points increase as you go down the group
      • The have similar formulas of compounds
      • The reactivity goes down as you go down the group
        • Chlorine reacts very vigorously with sodium. Iodine reacts very slowly with sodium
        • Can be shown by displacement reactions
          • Chlorine is more reactive than Bromine so it will displace the Bromine. The solution turns brown because because of the displaced Bromine
            • Cl2 + 2NaBr -> 2NaCl + Br2
          • A more reactive halogen will displace a less reactive halogen from a solution of one of its salts
      • Because they are so reactive you must use a fume cupboard, gloves and goggles
    • Formulaes
      • H2 (Hydrogen)
      • H2O (Water)
      • Cl2 (Chlorine)
      • Br2 (Bromine)
      • I2 (Iodine)
      • LiCl (Lithium chloride)
      • NaBr (Sodium bromide)
      • KI (Potassium iodide)

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