Chemistry is the study of the properties and structure of substances and of the changes they undergo. The term chemistry comes from the Arabic Al-Kimia, which means the art of transformation. Chemistry is all around us. It is ubiquitous in everything we do and everywhere we go. At home, there is the chemistry of our food, our medicines and our household objects. At work, there is the chemistry of semiconductors, which make up the electronic components.
The roots of chemistry can be traced to the phenomenon of burning. Fire was a mystical force that transformed one substance into another, and was thus an object of wonder, superstition, and even part of religious rituals. Fire affected many aspects of early societies, such as their diet, because it allowed them to cook food, and make pottery, specialised tools and utensils. Fire led to the discovery of glass and purification of metals. This was followed by alloys and the desire to make superior alloys for better armour and weapons.
The origins of chemistry can be traced back to the Egyptian alchemists. Alchemy was a quest to make gold from cheap metals. There was also a hope that alchemy would lead to the development of medicines to improve people’s health and a magic potion that would elongate life. Alchemy was practised by many cultures throughout history. The futile attempts to make gold and magic potions, led to the study of many chemical processes (crystallisation, calcinations, solution, sublimation, reduction, and so on) and devising of numerous procedures (heating to high temperatures in furnaces, distillation and so on). The ancient Egyptian tradition (5000 BC-400 BC) was continued by the Greeks (350 BC-650 CE), Arabs (650-1200 CE) and the Europeans (1300-1600 CE) leading to the birth of modern chemistry around the17th century. Since then there has been an ever increasing growth, leading to new material such as synthetic fibres, plastics, paints, detergents, pharmaceuticals, adhesives and many others. Our high standard of living depends heavily on the contributions of chemists to agriculture, manufacturing, pharmaceuticals and several other disciplines.
There are billions of substances with a variety of properties. But interestingly, all of them are made from basic elements numbering less than hundred. An element is a class of atoms which have the same number of protons in the nucleus. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium. Elements with atomic numbers higher than 92 are unstable and break into elements with small atomic numbers. The most convenient presentation of the chemical elements is in the periodic table of the chemical elements, which groups elements by atomic number (starting with hydrogen whose atomic number is one). Each element has a unique symbol: Hydrogen: H; Oxygen: O; Sodium, Na; etc. Due to its ingenious arrangement, groups, or columns; and periods, or rows, of elements in the table either share several chemical properties, or follow a certain trend.
Chemists often use reaction equations to summarise a specific reaction. As an example, the chemical reaction between hydrogen and oxygen produces water. The reaction equation is
The above reaction states that two molecules of hydrogen combine with one molecule of oxygen to produce two molecules of water; and a water molecule is made up of two hydrogen atoms and one oxygen atom.
There are several main branches. Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Organic chemistry is concerned with the compounds of the chemical element carbon. Carbon forms more compounds than any other element because its atoms can combine with one another to form very long chains. These compounds are the basis of all living matter. Inorganic chemistry is concerned with the compounds of all the other elements. Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living beings. Physical chemistry includes the study of the physical properties of compounds and the physical changes that occur during reactions, in particular the energetics and dynamics. Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning involving the techniques developed in physics and mathematics. Egyptian-born Ahmed Zewail pioneered the development of a new field known as Femtochemistry. This enabled for the first time to witness chemical events that occurred in femtoseconds (quadrillionths of a second, that is millionth of a billionth of a second, i.e., 0.000000000000001 second) using very powerful lasers. His technique is likened to Galileo’s use of his telescope which revolutionised astronomy. Ahmed Zewail was awarded the Nobel Prize for chemistry in 1999, unshared. The famous medieval Arab chemists include Jabir ibn Hayyan (721-815, Latinised name, Geber) and Muhammad ibn Zakariya al-Razi (854-925 CE, Latinised name, Rhazes).
Latin translation of one of Jabir ibn Hayyan’s books, Alchemiae Gebri done in 1545 and extensively used by the European chemists.
It is interesting to note that the haemoglobin found in blood and chlorophyll found in plants differ only by a single atom of iron and magnesium respectively. Haemoglobin is found in the vertebrates (animals with backbones including: mammals, reptiles, birds, fishes, amphibians). Invertebrates (animals without backbones including: insects, crabs, lobsters, snails, clams, octopuses, starfish, sea-urchins and worms) have another compound called hemocyanin which has two atoms of copper. Both haemoglobin and hemocyanin are used for respiration.
[The writer teaches at Department of Mathematics and Sciences, Dhofar University, Salalah, Sultanate of Oman. [email protected]]