A group in the periodic table is the vertical column in the periodic table. Groups usually have more significant periodic trends than periods and blocks, explained below. Chemists explain group trends by explaining that elements within the same group generally have similar electron configurations. The further you go down you go in the group the, the more reactive the element due to the weakening of electrostatic forces between the electrons and the nucleus.A period is the horizontal row in the periodic table. Groups have more significant periodic trends, there are regions where horizontal trends are more significant than vertical group trends, such as f-block.