Definition of an atom

All the chemical elements in this world are made of a universal unit called an atom. Atom represents the fundamental unit of any matter existing in this universe. An atom is comprised of a nucleus. Each atom has electrons associated with the nucleus. The other components present in an atom are protons and neutrons, which are present inside the nucleus. The only element free of a neutron is hydrogen.

Atom forms every object, whether solid, liquid, or gas. Even plasma is made up of atom. The size of an atom is very small, approximately 100 picometers. Using classical physics, it is almost impossible to detect the exact behavior of an atom due to its small size, which causes quantum effects. For example, a tennis ball's behavior is uncertain to predict.

It is known that the word "atom" originated from the Greek word "atomos." Atomos means uncuttable, defined because an atom is the smallest particle and cannot be made smaller. Rather than being founded on empirical evidence, this ancient concept was based on philosophical reasoning. These antiquated ideas are not the foundation of modern atomic physics. Early in the 19th century, John Dalton, a chemist, found that chemical elements appeared to combine with one another by basic units of weight. Assuming that these were the basic building blocks of matter, he chose to call these units "atoms."

The kinetic theory of gases, in contrast to Dalton's atomic theory, defines how gases behave physically, such as through diffusion, viscosity, conductivity, pressure, etc., rather than how they interact chemically to produce compounds.

John Dalton, an English chemist, discovered the "rule of multiple proportions" in the early 1800s after compiling experimental data obtained by himself and other researchers. He observed that when a certain chemical element is present in chemical compounds, its weight will vary in these compounds by ratios of small whole numbers. This pattern led Dalton to conclude that each chemical element interacts with other chemical elements through a fundamental and dependable unit of weight, which he named "atoms."

For instance, tin oxide comes in two forms: a black powder containing 88.1% tin and 11.9% oxygen and a white powder with 78.7% tin and 21.3% oxygen. In the black oxide, there is approximately 13.5 g of oxygen for every 100 g of tin, and there is approximately 27 g of oxygen for every 100 g of tin after adjusting these numbers. The ratio between 13.5 and 27 is 1:2. Dalton came to the conclusion that in these oxides, there are either one or two oxygen atoms for every tin atom (SnO and SnO2).

Iron oxides were also examined by Dalton. One type of iron oxide is a black powder with a composition of 78.1% iron and 21.9% oxygen; another type is a red powder with a composition of 70.4% iron and 29.6% oxygen. According to these adjusted numbers, there are approximately 28 g of oxygen and 42 g of oxygen for every 100 g of iron in the black oxide and red oxide, respectively. The ratio between 28 and 42 is 2:3. In each of these oxides, and there are two or three oxygen atoms for every two iron atoms (Fe2O2 and Fe2O3).

One last illustration: the compositions of nitrous oxide, nitric oxide, and nitrogen dioxide are respectively 63.3% nitrogen and 36.7% oxygen, 44.05% nitrogen and 55.95% oxygen, and 29.5% nitrogen and 70.5% oxygen. By adjusting these numbers, it can be determined that there are 80 g of oxygen and 140 g of nitrogen in nitrous oxide, 160 g and 320 g of oxygen and 140 g of nitrogen in nitric oxide, and 320 g of oxygen and 140 g of nitrogen in nitrogen dioxide, respectively. 80, 160, and 320 together make a 1:2:4 ratio. These oxides have the formulae N2O, NO, and NO2, respectively.