History of Periodic Table

The periodic table is a list of chemical elements organised according to their atomic number, electron configuration, and recurrent chemical properties. In the basic form, elements are presented in the reading sequence in increasing atomic number order. Then, rows and columns are created by beginning new rows and inserting blank cells, resulting in rows (periods) and columns (groups) that display elements with recurring properties (called periodicity). For example, all of the elements in group 18 are noble gases with few chemical reactions.

The periodic table describes the atomic structure of the elements as well as their chemical similarities and differences. The table is used by scientists to study chemicals and design experiments. It is used to create chemicals for the pharmaceutical and cosmetics industries, as well as batteries for technological devices. 

History of Periodic Classification

Antoine Lavoisier, a French chemist, attempted to classify elements as metals or nonmetals in 1789. Johann Wolfgang Döbereiner, a German physicist, discovered similarities in the physical and chemical properties of certain elements forty years later. He grouped them into groups of three in increasing atomic weight order and named them triads, observing that some properties of the middle element, such as atomic weight and density, approximated the average value of these properties in the other two in each triad.  

The publication of a revised list of elements and their atomic masses at the first international chemistry conference in Karlsruhe, Germany, in 1860, marked a watershed moment. They came to the conclusion that hydrogen would be assigned an atomic weight of one, and the atomic weights of other elements would be determined by comparison with hydrogen. Carbon, for example, has an atomic weight of 12 because it is 12 times heavier than hydrogen.  

Following are the points discussing the early history of Periodic Classification:

• Boyle defined an element in 1661 as those primitive and simple Bodies of which the next ones are said to be composed, and into which they are eventually resolved.
• Antoine Lavoisier, a French chemist, published the Elementary Treatise of Chemistry in 1789, which is widely regarded as the first modern textbook on chemistry. An element, according to Lavoisier, is a substance whose smallest units cannot be broken down into a simpler substance. The list of simple chemicals that Lavoisier felt could not be broken down further, including oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulphur, provided the basis for the contemporary list of elements. While many leading chemists were sceptical of Lavoisier’s new discoveries, the Elementary Treatise was written well enough to persuade the younger generation. Lavoisier’s descriptions of his elements, however, are incomplete because he only classified them as metals and nonmetals.
• From stoichiometric measurements and reasonable inferences, British natural philosopher John Dalton published a method in 1808–10 for calculating provisional atomic weights for the elements known at the time. During the 1810s and 1820s, many chemists adopted Dalton’s atomic theory.
• Johann Wolfgang Döbereiner, a German physicist, began to formulate one of the first attempts to classify the elements in 1817. In 1829, he discovered that he could group some of the elements into groups of three, with the members of each group possessing similar properties. He referred to these groups as triads.

Various Scientist explains the Periodic Classification as:

John Newlands

A British scientist named John Newlands was the first to organise the elements into a periodic table in order of increasing atomic masses. He discovered that each of the eight elements had similar properties and named this the law of octaves. He organised the elements into eight groups, leaving no room for undiscovered elements. 

Mendeleev

In 1869, Russian chemist Dmitri Mendeleev devised the structure for the modern periodic table, leaving gaps for elements yet to be identified. If he found that the elements did not fit into the group while arranging them according to their atomic weight, he would rearrange them. Mendeleev predicted the properties of some unknown elements and named them after them, such as eka-aluminium for an element with properties similar to aluminium. Later, gallium was discovered to be eka-aluminium. Some anomalies persisted, such as the placements of iodine and tellurium, which were not explained. To commemorate the 150th anniversary of Mendeleev’s publication, UNESCO designated 2019 as the International Year of the Periodic Table.

Lothar Meyer

In 1870, German chemist Lothar Meyer created a version of the periodic table similar to Mendeleev’s. He left space for yet-undiscovered elements but never predicted their properties. Mendeleev and Meyer were both awarded the Davy Medal by the Royal Society of London in 1882. Mendeleev’s predictions were later confirmed by the discovery of elements such as gallium (1875), scandium (1879), and germanium (1886), and his periodic table gained worldwide recognition. In his honour, the 101^st element was named mendelevium in 1955.

Henry Moseley

Subatomic particles did not exist in the nineteenth century. Henry Moseley, an English physicist, used X-rays to measure the wavelengths of elements and correlated these measurements to their atomic numbers in 1913. The elements in the periodic table were then rearranged based on their atomic numbers. This helped to explain discrepancies in previous versions that used atomic masses.

Timeline of periodic classification of chemical elements

1. In 1680, Robert Boyle discovered phosphorus and made it public.
2. In 1809, scientists discovered at least 47 elements, and they began to recognise patterns in their properties.
3. In 1863, English chemist John Newlands classified the newly discovered 56 elements into 11 groups based on their properties.
4. Dimitri Mendeleev, a Russian chemist, began developing the periodic table in 1869, arranging chemical elements by atomic mass. He predicted the discovery of other elements and left blank spaces in his periodic table to accommodate them.
5. Antoine Becquerel, a French physicist, discovered radioactivity in 1886. Ernest Rutherford, a Thomson student from New Zealand, named three types of radiation: alpha, beta, and gamma rays. Marie and Pierre Curie began researching uranium and thorium radiation and later discovered radium and polonium. The beta particles were discovered to be negatively charged.
6. In 1894, Sir William Ramsay and Lord Rayleigh discovered the noble gases, which were classified as group 0 on the periodic table.
7. J. J. Thomson, an English physicist, discovered electrons, which are small negatively charged particles in an atom, in 1897. Their exact charge and mass were determined by John Townsend and Robert Millikan.

Sample Questions

Question 1: What is a periodic table?

Answer:

The periodic table is a list of chemical elements arranged by atomic number, electron configuration, and chemical characteristics.

Question 2: What comprises a periodic table?

Answer:

In their most basic form, elements are presented in the reading sequence in order of increasing atomic number. Then, by starting new rows and adding blank cells, rows (periods) and columns (groups) are constructed to display components with recurring attributes (called periodicity).

Question 3: What is Newland’s law of octaves?

Answer:

John Newlands, a British chemist, was the first to organise the elements into a periodic table with increasing atomic masses. The law of octaves was named after his discovery that every eight elements had similar qualities. He divided the components into eight groups, leaving no gaps for unknown elements. 

Question 4: How did Moseley contribute to the periodic classification of elements?

Answer:

In the nineteenth century, there was no concept of subatomic particles. Henry Moseley, an English physicist, measured the wavelengths of elements with X-rays in 1913 and connected these results to their atomic numbers. On the basis of atomic numbers, he then reorganised the elements in the periodic table. This explained discrepancies in previous versions that used atomic masses. 

Question 5: What is Dobereiner’s triad?

Answer:

Physical and chemical properties of certain elements were found to be comparable by Döbereiner. He grouped them into triads of three elements in ascending order of atomic weight, noting that various attributes of the middle element, such as atomic weight and density, were close to the average value of these properties in the other two in each triad.