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Based on this law all the known elements were arranged in the form of a table called the 'Periodic Table'. Elements with similar properties recurred at regular intervals and fell in certain groups or families. The elements in each group were similar to each other in many properties. The elements with dissimilar properties from one another were separated. Mendeleev's periodic table contains eight vertical columns of elements called 'groups' and seven horizontal rows called 'periods', Each group has two sub -groups A and B. The properties of elements of a sub-group resemble each other more markedly than the properties of those between the elements of the two sub-groups.

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