Classification of Elements

All matter in our environment is made up of basic units called elements. Only 31 chemical elements were discovered in the year 1800. Around 63 additional elements were found after technological advancements in 1865. The periodic classification became necessary as a result of this. Over the years, many attempts have been made to classify elements, ranging from Dobereiner’s Triads to Newlands’ Law of Octaves, Mendeleev’s Periodic table, and the Modern Periodic Law. 

You will find the periodic classification of elements notes for class 11 below.

What Is The Need For Classification Of Elements?

One of the most important concepts of science is the classification of elements based on their properties and their simple construction. The first table of elements was written by chemist Dmitri Mendeleev in 1869. The periodic table of elements arranged the elements based on their atomic numbers and their physical and chemical properties. The table is always divided into rows, called periods, and columns, called groups.

Classification Of Elements And Periodicity In Properties

The chemical elements are put in a group in the long-form periodic table according to the order of the respective atomic numbers. The total number of protons inside the nucleus of an atom equals the element’s atomic number.

Long-form table shows the following properties:

• It has a total of 18 vertical columns and groups each.

• From left to right, these groupings are numbered from 1 to 18.

• It has seven horizontal rows which are called periods.

• The main elements of the group are those found in Groups 1 and 2, as well as in Groups 13 to 17. The above-mentioned elements are often referred to as normal, typical, or representative elements.

• Transition elements are the elements in Groups 3 through 12.

• The elements having atomic numbers from 58 to 71 (i.e. from Ce up to Lu) and exist following lanthanum (La), are known as Lanthanides. Actinides are the elements that have atomic numbers from 90 up to 103 (i.e. from Th to Lw). These are named f-block elements, as well as inner transition elements.

The current periodic table is used to study the elements nowadaysPeriodic classification of elements groups them based on their characteristics. The elements with similar properties are placed in a specific group, whereas those with different properties are placed in separate groups. Some empty spots have been left in the periodic table to accommodate elements that will be discovered in the future without disrupting the elements’ trending periodicity.

Importance of the Periodic Classification of Elements

1. Makes study of elements simpler: The grouping of elements gives us a predictable pattern wherein the characteristics of the elements often change. The periodic table simplifies and organises the studying of the chemical and physical properties of elements. 

2. Aids in the discovery of new elements: Although many elements have already been identified, there is still a chance that new elements may be discovered. Scientists can use a periodic table to determine trending features based on element attributes, allowing them to distinguish between new and existing elements. Furthermore, scientists are constantly working to discover new elements and investigate their properties.

Classification Of Elements

Dobereiner’s Triads – Origin of the Periodic Classification

Dobereiner ordered several elements with comparable properties in various groups consisting of three elements in 1829, with the middle element’s atomic mass almost equal to the average atomic mass of the first and third elements. He proposed some triads, which are mentioned below.

Dobereiner’s Triads’ Limitations

Dobereiner’s triads were useful for grouping together elements with comparable qualities, but he couldn’t put all of the elements known at the time into triads.

Newlands’ Law of Octaves

When elements are grouped in order of increasing atomic mass, John Newlands proposed the law of octaves, which states that every eighth element has properties comparable to the first. Because a similar link exists in musical notes as well, Newlands named it the law of octaves.

Drawbacks of Newlands’ Law of Octaves

• Only the element calcium was successfully classified. After then, no eighth member in the same group had the same attributes as the element above it.

• When noble gas components were identified later, they disrupted the overall arrangement.

Mendeleev’s Periodic Table

The physical and chemical properties of elements are periodic functions of the atomic masses of these elements, according to Mendeleev’s Periodic Law. The periodic table was created by Mendeleev, who organised the elements which were known at that time in order of growing atomic masses. Vertical rows of elements which have similar attributes were referred to as groups. Periods referred to the horizontal rows.

Key points about Mendeleev’s table:

• The elements are grouped in Mendeleev’s table in vertical rows called groups as well as horizontal rows called periods.

• The Roman numerals from I to VIII, and 0 represent the nine groupings. Group VIII is made with nine elements organised into three triads. The zero group contains elements that are either inert or noble gases, and all of the elements in the group have zero valency.

• In Mendeleev’s periodic table, there are seven periods (numbered between 1-7) or horizontal rows.

Importance of Mendeleev’s Periodic Table

• This made the study of elements more systematic. In other words, the table made it possible to predict the properties of elements with the help of the characteristics of a single element present in a particular group.

• This helped in discovering these elements at a later time.

• With the help of their anticipated placements and properties, Mendeleev adjusted the atomic mass of several elements.

Limitations in Mendeleev’s Table

• Hydrogen, along with alkali metals, is classified as part of Group IA. However, it shares several properties with group VII A halogens. As a result, its place in Mendeleev’s periodic table remains debatable.

• Although the elements present in Mendeleev’s periodic table are listed in order of atomic mass, the element which has a greater atomic mass sometimes comes before the element which has a lesser atomic mass.

• Isotopes of a given element have varying atomic masses and the exact atomic number, as we know. Because Mendeleev’s periodic table was created based on elements’ rising atomic masses, all of the isotopes of a given element are bound to be assigned to different positions.

• According to Mendeleev, elements that are placed together in a  group should be having properties that are similar. However, we see no similarity between the elements that are placed inside two different sub-groups of the same group.

• Elements with comparable properties have been grouped together in some circumstances.

• Lanthanoids and actinoids were placed in two separate rows at the bottom of the periodic table.

• There is no satisfactory explanation for placing elements with similar properties in a specific group.

Modern Periodic Law

The periodic function of the atomic numbers determines the physical and chemical properties of the elements. The current version of the Periodic Table is also known as the long version. Modern periodic law is used to create the long version of the periodic table, commonly known as the Modem Periodic Table. The elements have been organised in this table in order of increasing atomic numbers. There is the nomenclature for elements with atomic numbers greater than 100 here.

The Dobereiner’s Triads are often recognized as the first attempt to classify elements. Today, the modern periodic table is the widely accepted form of classification.

Conclusion –

 the classification of elements based on their properties and their simple construction. The periodic table of elements arranged the elements based on their atomic numbers and their physical and chemical properties.

Study of properties of elements became easier after arrangement of elements in periodic table.