CLASS XII CHEMISTRY

MENDELEEV'S PERIODIC LAW 

In 1869 , D.I Mendeleev  , a Russian chemist discovered an empirical law of classification of elements known as periods of Newland Law of Octaves.This is known as periodic law and stated as :

" The physical and chemical properties of elements are the periodic functions of their atomic weighs."

The Mendeleev periodic law includes 63 elements which are arranged in the order of their increased atomic weights in seven horizontal lines called Periods and eight vertical columns known as Groups. 

CLASS XII CHEMISTRY

LOATHER MEYER'S CONCEPT

In 1869 Loather Meyer , a German Chemist plotted the atomic volumes of elements against their atomic weights and found different curves . He observed that :

" Elements with similar physical properties occupied similar position in the curve " .

Loather Meyer concluded from this curve that :

" Physical properties of elements are periodic function of their atomic weights ".

 

DISADVANTAGES OF LOATHER MEYER'S CLASSIFICATION :

1 -The periodic classification is incomplete as compared to Mendeleev  periodic table which shows the remarkable prediction of discoveries of certain elements.

2 -Meyer's classification based on the physical properties related with atomic weights only.There is no empirical or logical basis for classification as found as that in Mendeleev periodic classification.

Chemistry class XII Chapter 1

NEWLAND'S LAW OF OCTAVES

In 1864 an English chemist Newland arranged the elements in the ascending order of their atomic weights . He observed that :

" The properties of every eighth element is similar to that of the first  ".

He called this regularity of elements as the law of octaves.

                               Li        BE        B      C      N     O       F

                              Na       Ma       Al      Si     P     S      Cl

ADVANTAGES OF LAW OF OCTAVES :

1- This law provided a basis for the classification of elements into groups having similar properties.

2- The law provided a scope to arrange all the elements into Tabular form.

DISADVANTAGES OF LAW OF OCTAVES :

1- Newland's law was only applicable for the first seventeen elements and broken down afterward e.g first two rows and three columns obey the law.

2- This arrangement did not include noble gases and heavy elements.

PERIODIC CLASSIFICATION

What is periodic table?

The periodic table is the tabular display of chemical elements , arranged on the basis of their atomic numbers , electronic configuration and chemical properties.

Why it is called Periodic?

Because the chemical elements repeat their chemical and physical properties after a fixed period.