MENDELEEV’S PERIODIC TABLE:-
When elements are arranged in order of increasing atomic masses the elements with similar properties occur at regular intervals.63 elements were known at that time. Mendeléev formulated a Periodic Law, which states that ‘the properties of elements are the periodic function of their atomic masses’.
Mendeléev’s Periodic Table contains vertical columns called ‘groups’ and horizontal rows called ‘periods’.
Mendeléev’s Periodic Table was published in a German journal in 1872. In the formula for oxides and hydrides at the top of the columns, the letter ‘R’ is used to represent any of the elements in the group. Note the way formulae are written. For example, the hydride of carbon, CH4, is written as RH4 and the oxide CO2, as RO2.