Chemistry - C3.1 - The Periodic Table - Revision Cards in GCSE Chemistry

C3.1.1 - The Early Periodic Table

19th century - many elements discovered, but didn't know about structure - tried to classify based on atomic weight
1863 - Newlands proposed law of octaves: similar properties repeated every 8th element - put the 62 known elements in table according to atomic weights - Ca didn't fit: idea wasn't accepted
1869 - Mendeleev produced table - left gaps for undiscovered elements so known elements were in groups of similar properties - missing elements found and fitted table: ideas accepted - became basis for modern periodic table

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Start of 20th century - found out about protons and electrons - soon developed models of electron arrangement - elements were arranged in periodic table in order of atomic numbers and lined in vertical groups
Groups of elements have similar chemical properties: same no of electrons on outer shell - same as group number
Within group, reactivity depends on total no of electrons - further down group = more shells: atoms get larger: electrons in outer shell less attracted to nucleus
Metals react: lose electron - reactivity increases going down group
Non-metals react: gain electron - reactivity decreases going down group

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Group 1: alkali metals - react with air and water
Soft solids at room temperature, low melting/boiling point - decreases going down group, low densities - Li, Na and K float on water
React with water to produce hydrogen and a metal oxide (alkali) - 2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
One electron in outer shell - lose it in reactions: ions have single positive charge
React with halogens in group 7, forming white/colourless salts crystals - 2Na(s) + Cl2(g) -> 2NaCl(s)
Compounds of alkali metals dissolve in water to form colourless solutions
Reactivity increases going down group: outer electron less strongly attracted to nucleus as no of shells increase and atom gets larger

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Halogens: non-metallic elements in group 7, 7 electrons in outer shell
Molecules made from pairs of atoms
Low melting/boiling points, increase going down
Room temperature: F - pale yellow gas, Cl - green gas, Br - red-brown liquid, I - grey solid - vapourises easily to violet gas
Form ionic compounds with metals, where the halide ions have a 1- charge - also bond covalently with non-metals to from molecules
Reactivity decreases going down group - more reactive halogen able to displace less reactive halogen from aqueous solution of halide compound
Reactivity decreases as attraction of outer electrons with nucleus decreases as no of shells increases

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