Modern Periodic Table Formula and Its Significance

In the late 18th century, Mendeleev created a periodic table due to his discovery of the periodic law. This was before scientists understood the internal structure of atoms. As atomic models and quantum theory developed, it became clear that the atomic number is the primary characteristic of a chemical element. This shift from Mendeleev's law to what we now know as the modern periodic law reflects this progress.

History of the Periodic Table

• It was Antoine Lavoisier who classified elements based on their properties in 1789, dividing them into gases, non-metals, metals, and earthly elements.
• In 1829 Johann Döbereiner tried to classify elements according to their chemical properties into triads, where the middle element's atomic weight was usually the average of the first and third. As an example, Lithium, sodium and potassium. However, he was not able to group all known elements accurately, so the law of triads was not accepted.
• The attempt to classify elements did not stop here and the English Chemist John Alexander Newland arranged the elements in order of increasing atomic weights in 1865. He discovered a periodic pattern in the arrangement. He showed that the physical and chemical properties of the eighth element are similar to the properties of the first element in that row. This generalization is known as the 'Law of Octaves'.
• Mendeleev published a paper in 1869, in the Journal of Russian Chemical Society, which outlined the periodic law - that element properties are periodic functions of their atomic masses. He was able to classify 63 known elements into a table with 8 columns and 7 rows, and even had space for additional elements to be discovered later.

Modern Periodic Law Definition

Features of Modern Periodic Table

• The elements are arranged in ascending order of their atomic numbers.
• Periods are seven horizontal rows and groups are eighteen vertical columns
• In a group, elements have the same number of outer electrons, but as we move from top to bottom, their physical and chemical properties gradually change.
• As we move from left to right, the properties of the elements gradually change. Atomic size gradually decreases.
• As compared to Mendeleev's periodic table, the modern periodic table contains more elements.
• Without the modern periodic table, it would have been impossible to study the chemistry of elements.
• It is easier to understand the properties of elements when they are classified in the modern periodic table.\

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Classification of Elements in the Periodic Table

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Modern Periodic Table Features & Significance

• According to their atomic numbers, the constituents of the table are arranged in increasing order.
• There are 7 horizontal rows and 18 vertical columns in the table, referred to as the rows.
• Each element in the table has the same physical and chemical properties. The outer electrons have the same number, but gradually change from the top to the bottom.
• When we move from left to right, the elements in the period change gradually. Atomic size decreases as well.
• Compared to Mendeleev's periodic table, this periodic table has about 118 elements.

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Position of Elements in the Modern Periodic Table

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