Using the periodic table to explore the most reactive elements. There are more than 100 elements in our universe, 81 of which are metals. In this programme, we use the periodic table to explore some of these elements and discover why some are more reactive than others. Science teacher Subathra Subramaniam visits Portobello Road market in London and learns why gold, silver and copper are ideal for making jewellery. She also examines the highly reactive alkali metals, which are found in group one of the periodic table.