They are:

  • The position of hydrogen isn’t explained clearly or properties of hydrogen resemble with both group I and VIII elements.
  • Chemically dissimilar elements are kept in the same group. E.g, copper, argon, all are kept together with Li, Na, K.
  • While arranging on the basis of increasing atomic mass potassium are kept earlier than argon. But argon is kept earlier than potassium in his periodic table.
  • Metals and non-metals aren’t placed separately.

The modern periodic law states that the physical and comical properties of elements are the periodic functions of their atomic numbers.

The features of modern periodic table are:

  • There are seven horizontal rows which are known as periods. There are seven periods, period one is very short, 2 and 3are short, 4 and 5 are long , 6 is very long and 8 is long but incomplete period.
  • There are IX groups in the modern periodic table. Among 9 group I to VIII are sub-divided into sub-groups A and B. Group VIII has three vertical columns and there is one group.
  • In group, I almost reactive metal in group VII a most reactive non-metals in 0 group inert gasses are kept.

The merits of Mendeleev’s periodic table are:

  • It is first effective classifications of elements.
  • It also predictedthe discovery of new elements.

They are as follows:

  • It helps for the prediction of new elements.
  • It gives the correct position of the elements.
  • It also helps to describe the simple properties of the elements.

It belongs to the third period. The full name of Na is sodium, mg is magnesium, Al is aluminum, SL is silicon, P is phosphorus, S is sulphur and CL is chlorine. Sodium elements are more reactive because it can easily lose its electrons.