Introduction to Periodic Classification of Elements

In this article we are about to learn how the elements were discovered and how they adjusted in today Periodic Tables with exact values. I'm going to show you guys, simple introduction to Periodic Classification of Elements.

Introduction to Periodic Classification of Elements

Introduction

The aim of the classification of the elements is to group together those elements which resemble each other in some respect and to separate those elements which are differ significantly. The best classification will clearly be that which brings together elements which resemble one another in the greatest number of ways.

In this way, there were some of best scientist of that time discovered 3 laws for separating the elements which are significantly similar in their properties.

1. Dobereiner's Triads

After the acceptance of atomic mass values universally, attempts were made to find out relations between properties of the various elements and their atomic masses. In 1829, J.W Dobereiner discovered that within a group of elements of three closely related in chemical properties, the atomic masses are either nearly the same (e.g. Iron, cobalt and nickel) or the atomic mass of the middle one element is the approximately the arithmetic mean of the other two elements. These are called Dobereiner's Triads.

The Graph of Dobereiner's Triads of Elements Classifications

2. Newland's Law of Octaves

The next attempt was made by an English chemist Newland between 1864-1869. He arranged the elements in the ascending order of their atomic weights (masses). He observed that the properties of every eighth element were similar to those of the first. he called this regularity of elements as the "Law of Octaves" and arranged most of the elements then known accordingly.

Newland's arrangement of element

Li= 7      Be=9.4    B=11    C=12    N=14    O=16    F=19

Na=23   Mg=24    Al=27.3    Si=28    P=31    S=32    Cl=35.5

In this classification, Li and Na and Mg; B and Al; C and Si; N and P, O and S; and F and Cl resemble in chemical properties.

Advantages and disadvantages of law of Octaves

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

ii) This law provided a wider scope to arrange all known elements into a tabular form.

iii) The periodic arrangement of elements did not include noble gases because they were not discovered then, and the heavier elements could also not be accommodated.

What is Hydrogen? And Methods of its Preparation

Introduction
Laboratory methods of preparation, properties and uses of hydrogen have already been discussed at secondary level. Here some more aspects of study of hydrogen will be considered.

Industrial Preparations of Hydrogen

In industry, hydrogen is manufactured by water, natural gas resource and ammonia. Methods are in the order of their importance:

1. Preparation of Hydrogen by Electrolysis of Water

When electricity is passed through water containing a small quantity of an electrolyte (an acid, a base or a salt), water decomposes into hydrogen and oxygen. Hydrogen collects at cathode and oxygen gas, a by -- product, is collected at anode with respect to their charges.

2H2O ----------------------> 2H2 (g)+ O2 (g)

The gases produced are in the purest form. This process is expensive and is used to produce hydrogen where electricity is available at cheaper rates.

2. Preparation of Hydrogen by Steam and Hydrocarbon Process

A mixture of steam and natural gas when passed over a nickel catalyst at 900 degree centigrades, produces a mixture of hydrogen and carbon monoxide commonly known as Water gas. Natural gas contains about 94.60%- methane.

CH4 (g)+ H2O  ----------------------> 3H2 (g) + CO(g) (Water Gas)

3. Preparation of Hydrogen by action of Steam on Coal

When steam is passed over red hot coke at about 1000 Degree Centigrades, a mixture of hydrogen and carbon monoxide (Known as water gas) is formed.

C (g)+ H2O  ----------------------> H2 (g) + CO(g) (Water Gas)

Hydrogen is obtained in free state by removing carbon monoxide from water gas. It is done by heating the mixture of two gases with more steam  at 500 Degree Centigrades in the presence of catalyst (Iron oxide or cobalt oxide). As a result carbon monoxide is changed to carbon dioxide which can easily be separated by dissolving in water under high pressure leaving behind free hydrogen gas.

    FeO

CO(g)+ H2 + H2O(g) ----------------------> CO2 (g) + 2H2 (g)

                                                                                             500 Degree Centigrades