<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configurations, and recurring chemical properties . This ordering shows periodic trends, such as elements with similar behaviour in the same column . It also shows four rectangular blocks with some approximately similar chemical properties . In general, within one row (period) the elements are metals on the left, and non-metals on the right . </P> <P> The rows of the table are called periods; the columns are called groups . Six groups have generally accepted names as well as numbers: for example, group 17 elements are the halogens; and group 18, the noble gases . The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized . The periodic table provides a useful framework for analyzing chemical behaviour, and is widely used in chemistry and other sciences . </P>

What is a row across the periodic table called