The periodic table was originally arranged in order of atomic mass. We now know that it is the electron arrangement that determines how the elements react. Which of the following is the correct description of how you work out the electron arrangement of the first 20 elements?

A French scientist, Antoine Lavoisier, gathered together a list of everything that he believed to be an element in 1789 - but in no particular order. An element was defined as a substance that could not be broken down further so some of his elements were in fact compounds. When scientists learned to measure the atomic masses of elements, they started to use this property to arrange the elements. The key step was taken by a Russian, Dimitri Mendeleev. Like Newlands, he arranged the elements in order of their atomic mass. The difference was that he left gaps where he thought that elements had... Show more

A French scientist, Antoine Lavoisier, gathered together a list of everything that he believed to be an element in 1789 - but in no particular order. An element was defined as a substance that could not be broken down further so some of his elements were in fact compounds.

When scientists learned to measure the atomic masses of elements, they started to use this property to arrange the elements.

The key step was taken by a Russian, Dimitri Mendeleev. Like Newlands, he arranged the elements in order of their atomic mass. The difference was that he left gaps where he thought that elements had not been discovered. When the first of these 'missing elements' was found and seen to have the properties Mendeleev predicted, scientists in the world of chemistry knew he was onto something. 

The modern periodic table is arranged in order of atomic number. We now know that it is the electrons and how they are arranged that give the elements their chemical properties.

Show less