Describe Mendeleev's Periodic Table

Mendeleev's entire table was based on one fundamental law: 'The properties of elements are the periodic functions of their atomic masses.'

This meant that if you arrange elements in increasing order of their atomic mass, elements with similar chemical properties will appear at regular intervals (periodically).

1. Groups and Periods: He arranged the 63 known elements into vertical columns called Groups (I to VIII) and horizontal rows called Periods (1 to 6).
2. Chemical Formulae basis: He relied heavily on the formulae of hydrides and oxides formed by elements to group them together.

1. Predicting New Elements: Mendeleev boldly left blank spaces in his table for elements that had not been discovered yet! He named them Eka-Boron, Eka-Aluminium, and Eka-Silicon. Years later, Scandium, Gallium, and Germanium were discovered and perfectly matched his predicted properties.
2. Correcting Atomic Masses: He corrected the accepted atomic masses of elements like Beryllium based on their position.
3. Noble Gases: When Noble Gases were later discovered, they could be placed in a new separate group without disturbing the existing table.

1. Position of Hydrogen: He could not give a fixed position to Hydrogen (it acted like both alkali metals and halogens).
2. Isotopes: Since isotopes have different atomic masses but identical chemical properties, they violated his rule of placing elements strictly by mass.
3. Wrong Order: In a few places, an element with a slightly higher atomic mass was placed before a lower one to maintain chemical groupings (e.g., Cobalt 58.9 came before Nickel 58.7).