Atom, Molecule, Compound, Element And Particle

In this section, I want to discuss the bases of chemical structures on the difference between atom, molecule, compound, element, and particle; to clarify the concepts necessary to understand air pollution and the type of media in which the pollutants remain.

Image 1: The sand characterizes by presenting all the mentioned objects.

The atom is the structural unit of the molecules, which means that many individuals atoms can join into larger structures; consequently, if you destroy a molecule, its result will be individual atoms. 

There are other smaller components in the standard model of particles in physics, called "fundamental particles" including leptons, quarks, and bosons. But in this case, the main components of the atom are the subatomic particles called electron, proton, and neutron, which give it its structure. 

There are different types of atoms. Depending on the type, each atom has a defined amount of components (electrons, protons, and neutrons). Which gives them different properties; these atoms are summarized in the periodic table; some examples are Carbon (C), Nitrogen (N), Oxigen (O), Iron (Fe), among others. 

When we have a material composed of atoms of only one type, it is called a chemical element; it is considered a pure substance that consists of equal atoms. So conventionally, all atoms in the chemical element have the same structure, for example, molecular Nitrogen (N2), molecular oxygen (O2), Carbon forms (C60), a bar of pure iron, a drop of pure gold, etc. Chemical elements may be solid, liquid, gaseous, or exist in other states of matter depending on their nature and the conditions of the place where they are found.

A molecule is a structure composed of 2 or more atoms, which can include one or different types of elemental atoms; that is why the name of "chemical compound" is usually assigned because it is compounded of several atoms. 

Molecules can be classified as organic, inorganic, or synthetic according to their origin. For example, organic molecules have Carbon-Hydrogen bonds, among these molecules, we find sugars, amino acids, colors, vitamins, hydrocarbons, ammonia, and more. Inorganic compounds lack these types of bonds, among them we find metal alloys, sedimentary rocks, carbon dioxide (CO2), carbon monoxide (CO), and more others. 

In general, organic and inorganic molecules obtained from nature can be classified into subgroups based on shared characteristics, such as their molecular structure, size, and charge. Synthetic molecules are created in a laboratory, they are usually designed by humans, so they may be very different in structure from those observed in nature, but synthetic methods can also produce natural molecules. 

Even though atomic synthesis methods such as fission and nuclear fission, humans have produced atoms that did not exist in nature; with the synthetic methods, the options are so wide that only the laws of physics and chemistry restrict them.

The particles are larger than all the previous ones, their ingredients may include molecules and atoms or even other smaller particles; can be formed of molecular compounds or pure elemental compounds, at the same time, mixtures between different molecules and elements are usually found. 

The particles can be produced in two ways, with the defragmentation of larger materials or with the aggregation of molecules and smaller particles. For example, if I have a wooden or metal rod and I start to scrape it, it will start to defragment, originating smaller particles, those residual particles are larger than atoms and molecules. Another example is snow, if I start to gather and compact small amounts of snow, in a while I will have a huge ball or a large particle. 

The size of particles is variable, from nanometers to meters, powders are characteristic by presenting a mixture of particle sizes; the powders are usually found as materials from nature and others types used for industrial and every day activities by man. For example, in a talc bag, the particles in the powder have a variety of sizes on the scale of nanometers, micrometers, and centimeters; these particle size variations are found in almost all powders, sand, soot, sugar, cement, etc. 

As these powders can be so fine and have very small particle sizes, they are easily carried by air currents and can stay suspended in the air for a long time. This is the reason why some types of dust and powders have the ability to pollute the air and reach our lungs. 

On the other hand, there are raw materials of another type, this material can easily change their physical state to enter the air mixture in the form of gases. For example, Water, Ethanol, hydrocarbons, Ethyl acetate, and other more; are compounds that will start boiling with a slight temperature change, becoming part of the gaseous mixture of the air. Many of these gases include industrial solvents and other toxic compounds that contribute to environmental pollution. In Image 1 we see a graphic representation of the structures mentioned above.

Image 2: from left to right. Atom, Molecule, and particle.

In the image, a helium atom on a scale of 1 Armstrong or 100 picometers; the field where the electron is found (black) and its nucleus in the center on a scale of 1 femtometer, the nucleus (enlarged section) is composed of protons and neutrons, as well as other subatomic particles. Next, there is a chemical molecule or compound, in this case, it is an organic molecule, Caffeine. The spheres in the molecule symbolize the atoms and the different colors indicate that the atoms are from different types; Carbon (gray), Nitrogen (blue), Oxygen (red), and Hydrogen (white) are linked by chemical bonds. In the case of being an elemental molecule, only atoms of the same type (of a single color) would be observed, varying in quantity according to the element. There are chemical elements such as noble gases (Helium, Neon, Argon, Krypton, Xenon, and Radon) that are naturally stable and do not need to bind to another atom to exist as an element. Finally, a particle is observed, composed of several types of molecules, standing out by its high surface concentration of lipids and its size on the nanometer scale. In the case of particulate matter (PM) that generates air pollution, similar structures usually occur, but their composition includes the polluting and toxic ingredients that we have previously discussed.

In summary, the fundamental particles make up the subatomic particles, together they give the atom its structure. Atoms assemble to form chemical molecules/compounds, which can be a mixture or include atoms of the same type, in the case of including only atoms of the same type, the molecule is considered pure and is called a chemical element. Molecules and some atoms are naturally aggregated as particles, forming larger structures, these particles may be microscopic such as nanoparticles or macroscopic such as sand, dust, smoke, among others. I hope this topic is clear and that you have achieved to understand in more detail the difference between atom, molecule, compound, element, and particle. If you still have certain doubts you can write them in a comment.