Development of the periodic table

• In the mid 19th century Dimitri Mendeleev devised the periodic table to organise all the known elements and even predicted new elements.
• The Elements are arranged in order of increasing atomic number
• The Nuclear symbol has the mass number at the top, the elemental symbol in the middle and the atomic or proton number in the bottom.
• Mendeleev found that the elements formed a pattern of chemical properties, and he formed a new row every time the pattern repeated. These are now called periods.
• Rows = periods
• columns = groups
• The reason element in groups have similar properties is because they have the same number of electrons in their outer shell. This determines how they react.
• Group 1 elements are more reactive as you go down the group
• Group 7 elements are less reactive as you go down the group
• Group 0 / Noble gasses are unreactive as they all have full shells.