The Evolution of Chemistry: A Journey Through Six Key Periods

The history of chemistry can be summarized into six periods. The first period is the Prehistoric era, ranging from the primitive era to 500 BC. The second period is the Greek period from 500 BC to 300 BC. The third period is Alchemy from 300 BC to 1500 AD. The fourth period is Guido da Vigevano's period from 1500 AD to 1660 AD. The fifth period is the Phlogiston period from 1660 AD to 1770 AD. The last period is the Modern period from 1770 AD to the present day.

The Prehistoric period began when humans started understanding combustion processes, producing fire, and using rudimentary tools for survival. In China, around 2000 BC, they developed artificial silk, paper, gunpowder, porcelain, and painting techniques. In Egypt, they used chemical knowledge for embalming practices and metalworking, pottery, fabric production, glassmaking, soap making, and construction using lime. They extracted metals like copper, gold, lead, silver, and iron.

The Greek period focused on philosophical and speculative aspects of chemistry. Empedocles, around 490-430 BC, proposed the universe consisted of four elements: earth, air, fire, and water, each associated with cold, wet, hot, and dry properties. He believed all substances were combinations of these elements and properties, unable to convert into simpler units. Empedocles' theories laid the foundation for understanding elemental composition.

The ancient Greeks, particularly Leucippus and Democritus, made significant contributions to chemistry by proposing the first atomic theory. They postulated that all matter is composed of indivisible and invisible atoms with different sizes, shapes, and weights, in constant motion and collision. This theory, although initially rejected by prominent philosophers like Plato and Aristotle, laid the foundation for modern atomic theory.

Leucippus and Democritus, the founders of the atomic theory, proposed that all matter consists of tiny, indestructible, and indivisible particles called atoms. These atoms, qualitatively identical but varying in size, shape, and weight, are in perpetual motion, constantly colliding and transferring motion. Their theory challenged the prevailing views of continuous matter held by philosophers like Plato and Aristotle.

Plato and Aristotle, influential philosophers of their time, opposed the atomic theory of Leucippus and Democritus. They believed in the continuity of matter and the existence of four elements proposed by Empedocles, rejecting the idea of atoms and void. Additionally, they introduced the concept of a fifth element, ether, as a spiritual and eternal substance beyond change.

The burning of the Library of Alexandria in 642 AD led to the loss of ancient chemical knowledge, causing a significant setback in scientific progress. However, this knowledge resurfaced in Egypt and Mesopotamia through alchemy, spreading across regions like Persia, India, China, Arabia, and the Roman Empire. Alchemy reached its peak during medieval Europe, where alchemists sought to discover the philosopher's stone and the universal panacea for transmuting metals into gold and achieving eternal life.

Alchemists, such as the renowned monk Basilio Valentín, dedicated their time to discovering elusive substances like the philosopher's stone. Despite not proving the existence of these substances, they made significant discoveries of chemical elements like arsenic, antimony, bismuth, and phosphorus. Basilio Valentín, in his pursuit of the philosopher's stone, instead discovered antimony and some of its compounds. Another alchemist discovered phosphorus while seeking clues in urine.

Alchemists also developed a wide array of laboratory equipment, including heating furnaces and distillation apparatus, to aid in their experiments and research.

The period of Iatrochemistry, also known as the period of medical chemistry, focused on exploring the medicinal properties of substances. Paracelsus, a Swiss physician from 1493 to 1541, integrated chemistry into medicine, emphasizing the importance of experimental methods in understanding diseases and treatments. He believed that diseases were caused by imbalances in the body's chemical composition and could only be cured through chemical substances.

The Phlogiston theory, introduced by George Stahl, proposed the existence of a substance called phlogiston, believed to be present in combustible substances like carbon and sulfur. According to Stahl, combustion and oxidation processes involved the loss of phlogiston. For instance, the reaction of sulfur with oxygen to form sulfur dioxide resulted in phlogiston loss. This theory was later proven erroneous but was significant in understanding combustion and oxidation processes in the past.

The Flogisto Theory, which involved the gain of flogisto, was prevalent in the past. For example, the reaction of iron oxide with carbon to produce CO2 and free iron was seen as a gain of flogisto. However, it is now understood that flogisto theory was erroneous, as it implied substances gaining or losing flogisto, which is not a valid concept in modern chemistry.

The modern period of chemistry began around 1770 with Antoine Lavoisier, who refuted the Flogisto Theory and explained processes like combustion, respiration, and calcination through oxidation. Lavoisier also introduced the use of the balance in chemistry, leading to the discovery of fundamental laws like the conservation of matter. He identified and separated oxygen (O2) and nitrogen (N2) as the main constituents of air, among others. Lavoisier's work marked the definitive separation between Flogisto chemistry and modern chemistry.

Various scientists made significant contributions to chemistry during this period. John Dalton formulated his atomic theory in 1803, building on ancient Greek atomist ideas. Amadeo Avogadro studied molecules and gas behavior, Wooller synthesized urea, Mayer and Mendeleev organized the elements in the periodic table, and Châtelier studied chemical equilibrium. Arrhenius proposed the theory of acid-base behavior. These contributions laid the foundation for modern chemistry and scientific understanding of atoms, molecules, and chemical reactions.

Chemistry continues to advance with researchers dedicated to making new discoveries for the benefit of humanity. The field of chemistry is divided into various disciplines due to the diverse range of objects studied. The present-day focus of chemistry involves ongoing research and exploration to uncover new knowledge and applications in different areas of science and technology.