Finding Order Among the Elements
Overview
The periodic table is one of the most fundamental tools of chemistry. It summarizes information about each element and reveals how the elements are chemically related to one another. The first widely accepted periodic table was published in 1869 by a chemistry professor named Dmitri Mendeleyev. He began work on his table hoping to help his students to learn about the elements. He ended up by creating a classification system that helped chemists predict new elements and that led to the discovery of the particles that make up atoms.
Background
One of the key developments that led to the periodic table was the determination of the atomic weights of the elements. In 1805 English chemist John Dalton (1766-1844) stated that every atom of an element has the same weight. This idea implied that it would be possible to measure the atomic weights of the elements. (It is now known that Dalton's hypothesis is incorrect; not all atoms of an element have the same weight. Atomic weights can be measured, but they usually represent an average.)
In 1809 Joseph Louis Gay-Lussac (1778-1850) proposed that when gases undergo a chemical reaction, they do so in simple whole number ratios of their volumes.
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