The periodic table
There are over a hundred elements. All substances are made from one or more of these elements. The modern periodic table is a way of showing how these elements can be ordered.
Before the development of the modern periodic table, there were other attempts to arrange the elements in a useful way, by scientists such as Döbereiner, Newlands and Mendeleev.
The modern periodic table is a chart containing the elements arranged in order of increasing atomic number. A vertical column, called a group, contains elements with similar properties. A horizontal row is called a period. The atomic number of the elements in a period increases from left to right along the row.
Before the development of the modern periodic table, there were other attempts to arrange the elements in a useful way. For example, Döbereiner arranged groups of three elements with similar properties into ‘triads'. Newlands and Mendeleev arranged the elements in order of increasing relative atomic mass.
Some attempts at arranging the elements were more successful than others. Newlands did not leave any space for undiscovered elements but Mendeleev did. Using his table, Mendeleev was able to successfully predict the properties of three elements that were not yet discovered.
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