The periodic table organises the chemical elements by their atomic number (number of protons in the nucleus), electron configurations and recurring chemical properties, in rows and columns. The rows are called periods and the columns groups, and generally within a period, the left side shows metals whilst the right shows non-metals. But how did we end up with the modern periodic table?
The earliest attempt to classify the elements was made by Antoine Lavoisier when he grouped the elements into gases, non-metals, metals and earths, based on their different properties. Whilst several other attempts were made to classify the elemts it was not until the 1860s that real progress began to be made as more accurate lists of atomic mass became available.
In 1869 a Russian chemist named Dmitri Mendeleev published what he called the Periodic System, the precursor to what we know as the Periodic Table. Although previous attempts had been made to categorise the elements, Mendeleev was the first to successfully find order and create the basis of the modern Periodic Table still in use today. Mendeleev’s approach was to write the properties of the elements on pieces of card and arrange them into different orders. By doing this he realised that if he put them in order of increasing atomic weight, certain types of elements regularly occurred.
When Mendeleev arranged the table, it also enabled him to predict the discovery of new elements, for which he left blank spaces. For instance, Gallium, was not discovered until after Mendeleev published the table but he had already predicted its properties and left a space for what he called ‘eka-aluminium’ – the element following aluminium in the table. The further discoveries of Scandium and Germanium helped cement the reputation of Mendeleev’s periodic table as everyone agreed that he had found a working system.
Scientists use the periodic table to understand why elements react in the way they do. They are able to form understandings and even discover new elements. Today we are still adding elements to the table, with the most recent addition being 117 in 2014, named Ununseptium. Our understanding is constantly evolving and developing, but the periodic table that Mendeleev posited in 1869 forms the basis of our understanding today.