Science class 10: Periodic Classification of Elements

Introduction :Periodic Classification of Elements

It is a simple technique for showing the components so that the elements having similar properties occur in the same vertical column or group. The modern period classification of elements is based on Mendeleev’s Periodic Table. Presently, there are 118 elements known for the periodic table, out of which only 94 naturally occur. All these have different properties. To study these elements with ease, it is required to organise them based on some pattern in their properties which is what we call Periodic Classification of Elements.

Features of Modern Periodic Table:

• Valency: The valency of a component is controlled by the quantity of valence electrons present in the furthest shell of its particle.
• Nuclear Size: It alludes to the range of a particle.

•       In a period, atomic size and radii decrease from left to right.
•       In a gathering, nuclear size and radii increments start to finish.
•       Metallic and Non-metallic properties:
•       Metallic character: An element tends to lose electrons from the outermost shell of an atom.
•       Non-metallic character: An element tends to gain electrons from the outermost shell of an atom.

Modern Periodic Table and Periodic Classification of Elements

Henry Moseley gave a new property of elements, ‘atomic number,’ which was adopted as the basis of the Periodic Table.

 Position of elements in Modern Periodic Table:

• The cutting-edge occasional table comprises 18 gatherings and 7 periods.
• Components present in any one gathering have a similar number of valence electrons. Also, the number of shells increases as one goes down the group.
• Components present in any one period contain a similar number of shells.
• Also, with an increase in atomic number by one unit moving from left to right, the valence shell electrons increase by one unit.
• Every period denotes another electronic shell getting filled.

Table of Elements in the Modern Periodic Table:

•       Main Group Elements – It includes elements in group 1 and 2 on the left-side of periodic tables. It also includes groups 13 to 17 located on the right-hand side of the periodic table.
•       Noble Gases – These elements are the ones which are present in group 18 and fills the outermost shells These are non-reactive elements.
•       Transition elements – These are present in middle blocks from group 3 to 12. These changes from electropositive to electronegative elements due to presence of two outermost shells.
•       Inner transition elements – It consists of 2 series of 14 elements where the first series is called lanthanides from elements 58 to 71. The second series consists of 14 rare earth elements and these are called actinides, elements from 90 to 103.
•       Metals and non-metals – They are located at the left-hand part of the periodic table where group one metals are called alkali metals and group two metals called alkaline earth metals. Non-metals are located on the right hand side of the periodic table.
•       Metalloids – The elements have properties of both metals and nonmetals.

What are Dobereiner’s Triads?

• It is based on atomic mass. Three members, gatherings have comparative properties when components are organised and arranged by expanding nuclear groups. 
• The nuclear mass of the centre component of the set of three is almost equivalent to the normal of the atomic masses of the other two elements.  For example, Triad of Li (6.9), Na (23), and K (39).

Merits of Dobereiner ‘s triads: 

Advantage of Dobereiner’s law is that it makes a look at elements in terms of groups of elements with similar chemical and physical properties.

Limitation:  

It neglects to organise ever-known components into sets of three.

Newland’s Law of Octaves: 

Elements are placed in order of increasing atomic masses, and the physical and chemical properties of every 8th element are a repetition of the properties of the first element.

Limitations:

• It was applicable only up to calcium (only for lighter elements).
• It adjusts two elements in the same slot having different properties. Co and Ni with Fluorine, Chlorine, Bromine, and Iodine.
• It was expected that the leading 56 components existed in nature, and no more details would be found.

Mendeleev’s Periodic Table:

• It is based on elements’ physical and chemical properties and atomic masses. 
• It thinks that the physical and synthetic properties of the components are the intermittent capacity of their nuclear masses.
• It contains vertical sections called gatherings and even columns called periods.

Merits of Mendeleev’s Periodic Table:

• Without disturbing the periodic table, Noble gases could be accommodated in the periodic tables without disturbing the periodic classification of elements.
• Vacant places were left on his table, which provided an idea for discovering new elements. For example, aluminium boron and silicon.
• His periodic table predicted properties of several undiscovered elements based on their position in Mendeleev’s periodic table.
• It helps rectify the far-fetched nuclear masses of specific components.

Limitations of Mendeleev’s Periodic Table:

• No fixed position for hydrogen: In Mendeleev’s periodic table, there was no correct position of the hydrogen atom. Model: Position of hydrogen with soluble base metals and incandescent lamp (seventeenth gathering).
• No place for isotopes:  Cl-35 and Cl-37
• No regular trend in atomic mass: Some elements with lower nuclear groups have positions before with higher atomic mass. For example, Ni-58.7 was placed before Co-58.9.

Conclusion :

The periodic table is one of the most important achievements in the field of chemistry. It is full of patterns that enable us to better understand the world around us. Without it, we would not have many of the products and medicine that we have today. The information gained from the periodic table can open up numerous windows of knowledge about the entire universe we live in. From this activity you should have a much more in depth understanding of the periodic table.