Mendeleev’s Periodic table: An Introduction
Mendeleev's periodic table was solely based on atomic mass whereas the modern periodic table relies on atomic numbers. The periodic table is the classified arrangement of chemical elements based on their physical and chemical properties. The modern periodic table we use was created after various alterations to the periodic table originally given by Dmitri Mendeleev. His structure was with columns and rows which is present in the modern periodic table also. The repetition of chemical properties of elements was observed by Mendeleev, hence the term period was used. The columns group together elements with the same qualities, so they are called groups and rows are periods as sets of elements repeat each time due to the similarity of their properties. Mendeleev did not validate isotopes which are atoms of same element but different weights. The modern periodic table is an improvement of the work of many chemists and scientists to create order out of chaos.
What is a Modern Periodic Law?
The Russian chemist 1869 created the basic framework for the modern periodic table, he would rearrange the elements if they did not fit into the group he was putting them into, this was the famous Dmitri Mendeleev, who is also known as the father of the modern periodic table. The modification of Mendeleev's periodic law is today called modern periodic law. The atomic number is equal to the number of electrons or protons in a neutral atom. Periodic law is chemistry's most relevant concept in dealing with chemical elements and their aspects such as electronegativity, atomic radius, or ionising power, it is a huge help to chemists as the elements are arranged in order of their similar chemical and physical properties.
What is a Modern Periodic table?
The modern periodic table is an arrangement of all elements, according to their increasing atomic number and similar chemical properties. They are organised in a tabular arrangement where a row is known as a period and a column is a group.
Elements arranged in the same group will be possessing the same valence electron configuration so they will have the same chemical properties.
Achievements of Mendeleev Periodic Table
Mendeleev kept some blank spaces in the periodic table for the elements which hadn't been discovered. Then he predicted the properties of certain elements before they were even discovered and on their discovery if they were found absolutely correct. Mendeleev's periodic table could fit in the noble gases when they were discovered. He ascertained the formulae of the oxides and hydrides as their basic properties for their classification in the periodic table. Mendeleev's periodic table helped in the correction of the atomic mass of some elements. It contained all known elements in order of increasing atomic mass.
Limitations of the Mendeleev Periodic Table
Besides being a path-breaking discovery, Mendeleev's Periodic table had quite a few demerits:
1. Anomalous pairs: Certain pairs of elements do not follow Mendeleev's principles, such as Cobalt has a higher atomic mass but comes before Nickel. Tellurium comes before Iodine.
2. Isotonic arrangement: According to Mendeleev's periodic law, isotopes had to be given separate places because of their different atomic masses.
3. Hydrogen: It wasn't given a fixed place as it resembles alkali metals and halogens also so that a correct position couldn't be given to it.
Interesting Facts
Mendeleev predicted certain elements but left a gap for them in the periodic table; he gave them hypothetical names such as Eka - aluminium/Eka - silicon.
Mendeleev was awarded the Copley medal, Davy medal and Demidov prize for his contribution.
Key Features
The modern periodic table is an arrangement of all elements according to their increasing atomic number and similar chemical properties, whereas Mendeleev’s Table, it's according to atomic mass.
There are many limitations in Mendeleev’s table that lead to the formation of the modern periodic table.
The elements in the same period of the modern periodic table will possess an increasing order of valence electrons.
The modern periodic table consists of all 118 elements, and maintains uniformity throughout.
FAQs on Making Order Out of Chaos: Mendeleev's Periodic Table
1. What is element 119 called?
Ununennium, also known as eka-francium, is the hypothetical chemical element having the atomic number 119 and the symbol Uue. They are still temporarily named and given symbols respectively until it is discovered and confirmed and a permanent name is decided upon. It is expected to look like an alkali metal with a +1 oxidation state. The energetic properties of its valence electrons portray that its first ionisation potential will be much higher than the oxidation potential.
2. Discovery of isotopes was first suggested by whom?
The existence of isotopes was first suggested in 1913 by a radiochemist, based on his studies of the decay of radioactive chains that gave evidence that about 40 varying radioelements exist between uranium and lead. In a letter Frederick Soddy the English radiochemist, published his discovery that elements have more than one atomic weight. The idea led to him winning the 1921 Nobel Prize in chemistry. Later isobars for nuclides were suggested by Alfred Walter Stewart in 1918.
3. What is Henry Mosley's contribution to the Periodic table?
Mosley was a graduate student in Ernest Rutherford's physics laboratory at the University of Manchester in England. He used the just then discovered X-rays to restructure the periodic table, suggesting that it was organised by atomic number rather than by atomic weight. He was responsible for giving the information that the structure of the atom is vital in understanding the elements themselves.
