Chemistry unit three (part one)

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  • Chemistry unit three (part one)
    • The periodic table
      • The modern periodic table
        • The atomic (proton) number of an element determines its position
        • The number of electrons in the outer shell determines the chemical properties
        • The group number equals the number of electrons in the outer shell
        • The distance between the outer electrons and the nucleus and the number of occupied shells can help explain trends of reactivitiy
      • The early periodic table
        • The periodic table of elements was created to classify the elements. It arranges them into a pattern in which similar elements are grouped together
        • Newlands' table put elements in order of atomic weight but failed to account for unknown elements
        • Mendeleev's table left gaps for unknown elements and so provided the basis for the modern periodic table
    • Groups
      • Group 1 (alkali metals)
        • They react readily with air and water.
        • They all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide
        • They form positive ions with a 1+ charge in reactions to make ionic compounds.
        • Their compounds are usually white or colourless crystals that dissolve in water to produce a colourless solution
        • Their reactivity increases going down the group
      • The transition elements
        • Compared with the alkali metals they have a much higher melting point and higher densities. They are also harder and stronger and less reactive
        • Don't react vigorously with oxygen or water
        • Can form ions with different charges and in compounds that are often coloured
        • Are important industrial catalysts
      • Group 7 (halogens)
        • Non-metallic elements. They exist as small molecules made up of pairs of atoms.
        • They have low melting and boiling points that increase going down the group.
        • At room temperature fluorine is a pale yellow gas, chlorine a green gas, bromine a red-brown liquid and iodine a grey solid. Iodine easily vaporises to a violet gas
        • Have seven electrons in their outer shell so when they form ionic compounds with metals, their halide ions have a 1- charge.
        • Form covalent bonds by sharing electrons
        • A more reactive halogen can displace a less reactive halogen to form a solution of one of its salts
        • The reactivity decreases going down the group


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