Classification of Elements and Periodicity in Properties

In chemistry, the periodic table of elements represents a significant milestone. It is regarded as one of the most significant scientific accomplishments. Individually studying the chemistry of more than a hundred elements and their associated compounds is tough. Nevertheless, chemists such as Johann Wolfgang Döbereiner, John Newlands, Dmitri Mendeleev, and Henry Moseley thought about correct element categorisation in the nineteenth century. They worked tirelessly to analyse and classify these elements. Let’s understand the classification of elements and periodicity in properties study material in detail!

Historical Study of Periodicity

• Dobereiner’s Triads (Law of triads):

In 1817-1829, German chemist Johann Dobereiner divided the elements into triads, groups of three elements with similar chemical properties.

He also demonstrated that the atomic weight of each triad’s middle element was equal to the arithmetic mean of the atomic weights of the other two components.

For example, lithium is the first element in the alkali metal group (Dobereiner’s triad), sodium is the middle member, and potassium is the third element in the triad.

Drawback of Dobereiner’s Classification:

Dobereiner’s classification approach could only arrange a small number of components in triads from those known at the time. As a result, the concept of triads does not apply to all of the known elements at the time.

• Newland’s Octaves Law:

In 1865-66, the English chemist John Newland organised the elements in ascending order of their atomic weight and discovered that every eighth element had identical qualities to the first, analogous to the eighth note of the musical scale.

This law states that sodium, the eighth element from lithium, has properties comparable to lithium, the first element. Those similar observations have been made for Be and Mg, B and Al, and so on.

Newland’s classification has some limitations:

(I) It failed miserably when dealing with heavier elements than calcium (Ca).

(ii) The idea of octaves was born when noble gases were discovered because beyond calcium, there is a difference of 18 instead of 8.

• Lothar Meyer’s Arrangement:

A German chemist, Lothar Meyer, created a graph between the elements’ atomic volumes and atomic weights and discovered that atoms with comparable properties were clustered together on the curve.

(I) The peak of the curve is occupied by alkali metals.

ii) Alkaline earth metals are at the bottom of the curve.

iii) Metalloids are at the bottom of the curve.

iv) Halogens are arranged in ascending order on the curve.

As a result, it revealed specific patterns among the elements. Lothar Meyer proposed that the physical properties of the elements are a periodic function of their atomic weights, i.e., the base of Mendeleev’s periodic table, on this basis.

Mendeleev’s Periodic Law:

“The physical and chemical properties of elements are a periodic function of their atomic weights,” Mendeleev, a Russian chemist, noted in 1869. In other words, when elements are organised in increasing order of their atomic weights, elements with comparable properties are repeated at regular intervals, according to this law.

Mendeleev’s Periodic Table:

Mendeleev grouped 63 – 65 elements known at the time in ascending order of their atomic weights in the form of a table published in 1905 and known as Mendeleev’s periodic table. However, it should be emphasised that noble gases had not yet been discovered at the time.

The original Mendeleev table has eight vertical columns (designated groups I-VIII) and six horizontal rows (called periods). Roman numerals were used to represent the group number.

Advantages of Long-form of Periodic Table:

• It is based on atomic number and electrical configuration, which are more fundamental properties.
• It is capable of totally separating metals from non-metals.
• Dissimilar elements do not fall together due to the separation of two subgroups.
• It identifies the relationship between the position of parts and their electronic configuration.
• Each period’s conclusion is more logical.
• Property periodicity can be visualised.
• The periodic table’s greatest advantage is that it can be divided into four blocks: s, p, d, and f-block elements.
• This element arrangement is simple to learn and duplicate.

Periodic Properties of Elements

Some of the Periodic Properties of Elements are:

Atomic Size (Atomic Radius): 

Suppose an atom is thought of as spherical; its radius is a good indicator of its size (i.e., atomic radius). It can be described as the distance between the nucleus’s centre and the outermost electron-carrying shell. The unit of measurement is angstrom (Å) or picometer (pm).

Ionisation Potential (or energy): 

Ionisation energy, also known as enthalpy or potential, is the energy needed to eliminate the most loosely attached electron from an isolated, neutral gaseous atom.

Electron Affinity (Electron Gain Enthalpy): 

Electron affinity is the amount of energy released when an electron is added to a neutral gaseous atom of an element to generate a negative gaseous ion.

Electronegativity (EN): 

Electronegativity is the ability or tendency of an element (atom) in a molecule to attract the shared pair of electrons to itself.

Valency: 

The number of electrons obtained, lost, or shared with other atoms in the production of compounds determines an element’s valency.

Oxidation States: 

In modern thinking, the oxidation number or oxidation state has almost completely superseded valence. An atom’s remaining charge as an element in a specific species is known as the oxidation number or state.

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Conclusion

riodic table, the elements are listed to increase the atomic number. These elements show a variety of interesting patterns, and we can predict their chemical, physical, and atomic properties using the periodic rule and table construction. 

Understanding the classification of elements and periodicity in properties requires looking at the electron configuration of the elements; all elements seek an octet formation and will gain or lose electrons to achieve this stable configuration.