A chemist is a scientist who studies and does research in chemistry and its various processes. In broader terms, chemists study matter, its properties, their composition, the chemical reactions happening and how those chemical reactions result in new products and so on.
To celebrate the necessity of chemistry and its sub-fields and how this field has revolutionized and transformed during the last decades, the top scientist of the field are being presented here along with brief overviews of their achievements and contributions.
Antoine-Laurent de Lavoisier / Antoine Lavoisier
Antoine Lavoisier, also known as the father of modern chemistry, was a French chemist. He was born in 1743 and died in 1794. He has been widely known for his influences in the fields of both the histories of chemistry and biology. The most important of his contributions in the field of chemistry include oxygen theory, presenting the concepts of stoichiometry, the nomenclature of chemicals, and chemical revolution.
It was during the late 1772 when the phenomenon of the combustion of oxygen got Antoine’s attention which enabled him to make his most significant contribution in the field.
The very first experiments by Antoine were on phosphorous combustion which were reported to the academy on 20th October (1772) in the form of a letter. This report stated that when phosphorous is burned it increases in weight upon burning. Moreover, the phosphorous also combined with a huge quantity of air to produce the so called acid spirit of phosphorous upon burning.
This first report was accompanied later by a second report in which he extended his keen observations and conclusions about the experiment. This report also contained the burning of sulfur along with phosphorous and he implied from his results that the changes which took place in the burning of sulfur and phosphorous might also be applicable to all substances that increase their weight after combustion.
Antoine was one of the few researchers who have been the pioneers of doing quantitative chemical experiments. In doing so, he used to carefully weigh the reactants and products in closed vessels so that no gas exchange occurs between the reactions and the outside environment. Such experiments led him to establish the fact that the total mass of matter during chemical reactions remains the same (in 1774).
Dmitri Mendeleev was a Russian chemist and an inventor best known for his formulation of the Periodic Law and periodic table of elements. He was born in 1834 and died in 1907. Also, his farsightedness led him to formulate Periodic Law in such a manner that not only this was then used to correct the properties of already known elements but also enables the prediction of elements yet to be discovered.
Discovery of Periodic Table
In 1863, when there were only 56 known elements, several scientists tried to define the periodicity of these elements. Initially, the law od octaves was presented by John Newlands which tried to put the elements in a periodic manner in view of their atomic weights. Similarly, Lothar Meyer also tried to arrange the elements periodically according to their valence properties. But each of these had their own flaws associated with them.
It was about 1867 when Mendeleev was preparing a textbook of chemistry which led him to make the most important discovery – the periodic table. In his textbook, Mendeleev was trying to classify the elements on the basis of their chemical properties where he noticed some patterns.
According to Mendeleev himself, it was a dream in which he saw all the elements perfectly fell into appropriate places as required which he immediately noted on a paper after waking up (except one place which he corrected later on).
After Mendeleev developed the periodic table with all elements known at that time, he published it in a Russian journal. Also, Meyer published his periodic table too within a few months which was virtually identical to that of the Mendeleev’s. However, Mendeleev’s table made an important distinction in that it accurately predicted the properties of germanium, gallium and scandium.
Due to Mendeleev’s unmatchable work on the periodic table, he is often called as the Father of the Periodic Table too.
Linus Carl Pauling – an American chemist, chemical engineer, biochemist, and a peace activist – was born in Portland, Oregon – a state of US. He lived from 1901 to 1904 during which he made spectacular achievements of his career by publishing more than 1200 papers and books. He has been the winner of two noble prizes – one in 1954 for his work in the field of chemistry and the other in 1962 for his peace activism. Now let us dig a little deeper into his feats one by one.
Chemical Bond and its Nature
Pauling started working on the nature of chemical bonds in the late 1920’s which led him to publish his research. Then after being appointed as a lecturer in chemistry in Cornell University, he delivered a series of lectures on this subject meanwhile completing his famous textbook ‘The Nature of Chemical Bond’. Due to this work primarily, he got his noble prize in chemistry in 1954.
He also introduced the concept of orbital hybridization. It is due to this concept that the orbitals are considered to have partaken the effect of each other. For example, the one 2s and three 2p orbitals on carbon are mixed to form four orbitals of equivalent energy in the type of hybridization known as sp3 hybridization. Other types of hybridizations include sp2 and sp hybridizations with their own properties.
Another area of chemistry which he explored was the relationship between ionic and covalent bonding (ionic bonding is the type of bonding in which electrons are transferred between atoms whereas in covalent bonding the electrons are shared between the atoms). Pauling viewed these two bonding types as mere extremes and explained with the help of quantum mechanics that a polar molecule AB can be described as a combination of the wave functions of both ionic and covalent bonding.
He also made great efforts in describing the structure of the aromatic compounds and came up with a resonance theory for them by implementing quantum mechanical approaches to explain them. We all know that the best explanation of the structure of the simplest of the aromatic compounds i.e., benzene has been presented by the Fredreich Kekule in which the alternate double bonds shuffle their positions via rapid interconversion. However, Pauling proposed a superposition of the bonds rather than their rapid interconversion. Also, this phenomenon resembles to the concept of hybridizations and polar bonding too.
Ionic Crystals Structures
Pauling also worked on predicting and explaining the structures of the ionic molecules which he published in 1929 in the form of five rules which are:
- The ratio of cation and anion radii,
- The strength of electrostatic bonds,
- The sharing of corners, edges and faces of a polyhedron,
- The presence of different cations in the crystal, and
- The parsimony rule.
Work on Biological Molecules
The major influence on Pauling to work in the field of biology came in the 1930’s when the funding priorities shifted more towards biological sciences which made him to take a decisive shift of interest to explore new fields. In doing so, he interacted with great biologists of that time such as Thomas Hunt Morgan, Theodosius Dobzhanski, Calvin Bridges and Alfred Sturtevant.
One of his early works in the field of biology included the study of hemoglobin molecule and how its structure changes when it binds with oxygen molecules. This work led him to study the protein structures in more details for which he tried to use X-ray diffraction analyses but this could not prove much successful as this technique was far less amenable for crystals of biological molecules.
Pauling, along with Robert Corey and Herman Branson, correctly proposed the secondary structural elements of proteins – alpha helices and beta sheets. Moreover, they also presented the assumptions that it is possible that the one turn of helix may contain a non-integer number of amino acids, which we now know is true.
Pauling also proposed the triple helical structure of the DNA but since this model contained a number of mistakes, it was faced with great criticism and conflict. Moreover, he also studied enzymatic reactions and pointed out that enzymes work by stabilizing the transition state of the reactions.
Work in the field of Molecular Genetics
Pauling, with Harvey Itano, Ibert wells, and Seymour Jonathan Singer, published their work on sickle cell anemia and demonstrating it to be a molecular and genetic disease in 1949. They demonstrated that individuals with this disease contain a modified form of hemoglobin in their blood cells.
For this, they used the technique of gel electrophoresis to show the difference between normal and diseases hemoglobin proteins. This was also the first demonstration that Mendelian inheritance also determines the physical properties of the proteins.
Atomic Nucleus’ Structure
Pauling presented a spheron model to explain the structure of the atomic nucleus. According to this model, the nucleus can be viewed as a cluster of nucleons containing different sub atomic particles.
John Dalton was a British chemist who lived from 1766 to 1844. Besides being a chemist, he was also a microbiologist and a meteorologist too. He is rightfully known for his work on the identification of the heredity of color blindness, his law of partial pressures of gases and explaining the behaviors of atoms taking into account their weights.
Dalton’s work on color blindness stems from his and his brother’s color blind condition which led him to think that this disease must be hereditary in nature. His first paper on color blindness was entitled ‘Extraordinary facts relating to the vision of colors’. The Dalton’s theory of color blindness lost credence in his lifetime but later on the examination of his preserved eyeballs demonstrated that he had a type of color blindness now known as deuteroanopia.
In 1801, Dalton presented his four essays entitled ‘Experimental Essays’ in which he had worked on the composition of mixed gases, the effects of the pressures of the steam or the vapor pressures, the effects of temperature in vacuum and air, and the principles of thermal expansion of gases. In the following years he came up with laws of partial pressures of gases also known as Dalton’s laws nowadays.
Dalton’s Atomic Theory
The most important work of Dalton is his work for the atomic theory in the field of chemistry. Although his atomic theory remains incompletely understood, some of its inherent postulates are as follows:
- Atoms are the building blocks of all the elements,
- An element is made up of atoms identical in size, shape and properties, while different elements have different atoms associated with them,
- Atoms cannot be destroyed, created or subdivided,
- Chemical compounds are formed by the combinations of atoms of different elements, and
- Chemical reactions involve the separation, combination and rearrangement of atoms.
Dalton’s Atomic Weights
Dalton also presented the concept of atomic weights of atoms. He presented the concept of relative atomic weights according to which the weight of an atom of an element can be calculated in relevance to the weight of a hydrogen atom which is considered conventionally as 1. This led him to publish his table of relative atomic weights of six elements.
Marie Curie is the first lady to win Nobel prizes, first in the field of physics and then second in chemistry. She is also the first person for winning two Nobel prizes. With her husband Pierre, her work on the discovery of radioactive elements polonium and radium, and later her work on the development of X-rays account for her most spectacular feats in the world of science.
Discovery of Radioactivity
The discovery of radioactivity by Marie Curie began with the work of another scientist named Henri Becquerel who was working on the properties of X-rays by using elements that give fluorescence naturally.
At that time, it was believed that when uranium is placed in the sunlight it gets charged and can be used to develop photographic films (because it emits energy formerly stored from the sunlight).
But the surprise cam in Becquerel’s life when he noticed that the energy emitted from uranium indeed developed films without even prior charging from sunlight. Upon studying this radiation, he found them to be charged negating the fact that they were X-rays (as these rays are neutral).
Marie Curie, along with her husband, started investigating this phenomenon further and coined the term radioactivity for it. When the Curies extracted uranium, they found more radioactivity in the leftover than the pure form, which led them to conclude that the ore contained more than one radioactive elements. This is how they discovered polonium and radium from these experiments.