Periodic Table Development

KEY POINTS:

• Scientists attempted for centuries to place the elements in some kind of order. They based the organisation on patterns and trends observed in both physical and chemical properties.
• Döbereiner’s triads and Newland’s octaves were early examples of the grouping but with one major flaw – they did not leave gaps for undiscovered elements.
• Dmitri Mendeleev had both the bravery and the foresight to arrange the elements in his periodic table with gaps for at least three undiscovered elements at that time (circa 1869).
• Mendeleev successfully predicted the atomic mass, physical and chemical properties of these undiscovered elements (gallium, for example). Since then more and more elements have been discovered that fit perfectly in Mendeleev’s table.
• It is Mendeleev’s periodic table that we still use today for classification of the elements. It is an invaluable tool in all aspects of chemistry.