What do the numbers on the periodic table mean?

2019 marks the UNโ€™s International Year of the Periodic Table or #IYPT. Itโ€™s 150 years since Dmitri Mendeleev presented his organisation of chemical elements to the world. The periodic table is used daily by chemists and other scientists as reference resource for the ingredients of the universe. Ancient Greeks defined โ€œelementsโ€ as one of the …