Families of Element

Johann Döbereiner (1780–1849) made one of the earliest attempts to organize the elements into families in 1829, when he observed that for certain groups of three elements, called triads, the properties of one element were approximately mid-way between those of the other two. However, because the number of elements known to Döbereiner was far less than it is today, the number of triads that he was able to find was very limited.

In 1864, John Newlands (1837–1898) noticed that when the known elements were arranged in order of increasing atomic weight, every eighth element showed similar properties. This observation, which was at first dismissed by the chemical community as being purely coincidental, is readily explicable using the modern periodic table and the concept of families of elements.

After organizing the elements known in 1869 so that those with similar properties were grouped together, Dmitri Mendeléev (1834–1907) predicted the existence and properties of several new elements. The subsequent discovery of these elements, and the accuracy of many of Mendeléev's predictions, fully justified the notion that the elements could be organized into families. Today, we recognize that the basis for this classification is the similarity in the electronic configurations of the atoms concerned.