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4.1 Organizing the Elements Atomic Mass – the average mass of an atom of an element (of all occurring isotopes) Mendeleev – organized the known 64 elements into a periodic table which made the study of chemistry more manageable Mendeleev’s periodic law- if the elements are arranged according to their atomic mass, a pattern can be seen in which similar properties occur regularly 4.3 Activity Modern Periodic Law – If the elements are arranged according to their atomic number a pattern can be seen in which similar properties occur regularly. Atomic radius – The distance from the nucleus to the outer edge of the atom 4.4 Groups of Elements Chemical Group – the set of elements in the same column that have similar physical and chemical properties Noble Gases o Group 18 o Full outer orbit o Unreactive Alkali Metals - Group 1 - 1 electron in outer orbit - Very reactive - Never found alone in nature always in a compound Halogens - Group 17 7 electrons in outer orbit Very reactive Found in nature as compounds Hydrogen Lauren Gill O’Brien Grade 9 Science - it is colourless, tasteless, odorless highly flammable reacts with halogens Metalloids - have both metal and non-metal properties - not in a group together but zig zag between the metals and non-metals - silicon o shiny, silvery – like metals o not malleable, poor conductor – like non-metals Periods – horizontal rows of elements - show similarities Lauren Gill O’Brien Grade 9 Science 4.6 Metals – alloys Polymers – Wool, leather, linen, cotton - glue, rubber - nylon, plastics -a material made of long molecules Ceramics – stone, pottery, flint -glass - a material made by heating minerals and rocks Composites – Straw/clay -fiberglass - a material formed by combining two other materials. 4.7 Ozone Lauren Gill O’Brien Grade 9 Science