The periodic table GapFill

In the periodic table, elements are ordered by their  atomic massreactivityconductivityhardnesscolouratomic number. Columns in the periodic table are called  elemental regionsperiodssetsgroupsseriesclasses, and all the elements in the same column have similar reactions because they have the same number of  ionsatomsisotopesneutronselectronsprotons in their outer shell. Over time, new ways of organising elements have been invented. Elements were first put in order by  how useful they werehow common they werenumber of isotopesorder of discoveryatomic weightdiameter, but some elements were in the wrong group.  Max PlanckAlfred NobelLinus PaulingDmitri MendeleevErnest RutherfordIsaac Newton changed the order and left gaps for  unreactiveundiscovereduselessmagneticdangerousradioactive elements, based on the chemical properties of the elements.

Elements which form positive ions when they react are called metals, and elements which do not form positive ions when they react are called  ionsalloysnoble gasessaltscarbonatesnon-metals.