The Periodic Table of Elements

The vertical columns on the periodic table are called groups. Elements in a group have similar properties, because the atoms of the elements have the same number of valence electrons in their outer shell. For example, atoms in Group 1 have one valence electron while atoms in Group 2 have two valence electrons. The valence electrons are often involved in chemical bonding, making certain groups more likely to react with other elements. An element from Group 1 will combine with an element from Group 17 in a one to one ratio. For instance sodium (Na) combined with chlorine (Cl) forms sodium chloride, NaCl.