The nineteenth century was the golden age for the discovery of elements.

Sophia Wong Candidate number: 7397

“The nineteenth century was the golden age for the discovery of elements. Scientists began to look for patterns of behaviour between elements.”*1 Johann Döbereiner, a German chemist, was the first to attempt to categorise the elements. He used their atomic weights, which we now know as atomic masses.

In 1863, John Newlands, produced something that he called the ‘Law of Octaves’. He used this to produce his own version of the periodic table, but Newlands came across some problems. “After about 20 elements his table became ragged,”*2 Newlands had left no gaps for undiscovered elements and even had to put two elements in one space.

It was Dimitri Mendeleev, a Russian chemistry professor, in 1869 that produced a much improved table. He amended many of the atomic weight values and left gaps for undiscovered elements.

“Mendeleev was so confident of the basis upon which he had drawn up his table that he made predictions about elements which had yet to be discovered.”*3 Since Mendeleev’s table all the gaps he left have been filled, three of the five elements whose properties he predicted were found within fifteen years, and a whole new group has been introduced – the Noble Gases.

Atomic spectroscopy is one way which has been used to increase our knowledge about chemical elements. It excites atoms which then emit light; this light can be split by a prism which will show the ‘emission spectrum’. It is used widely to find the composition of a sample, such as blood, or to estimate the content of a substance.

“The sequence of lines in an atomic spectrum is characteristic of the atoms in the element.”*5

This technique was only discovered in the 1860’s, so was a very new method when Paul Emile Lecoq de ...