Have you ever wondered what everything is made of? What gives different substances their distinctive properties? Why are substances solids, liquids, or gases? Why are they soft or hard; light or heavy? And if we probed matter at the deepest possible level, how small would it be? Certainly we are not intuitively equipped to interpret the world at the microscopic scale. When it comes to extremely small things, it’s out of sight, out of mind. Our senses operate on a different field altogether. Scientists, however, have somewhat closed the intuitive gap. They have identified the atom as the basic structure of matter—the building blocks of nature. In A Short History of Nearly Everything, Bill Bryson writes:
“The Great Caltech physicist Richard Feynman once observed that if you had to reduce scientific history to one important statement it would be: ‘All things are made of atoms.’ They are everywhere and they constitute everything. Look around you. It is all atoms. Not just the solid things like walls and tables and sofas, but the air in between. And they are there in numbers that you really cannot conceive.”
Although understanding the behavior of atoms is far beyond most of us, the basic components and arrangements that make up the atom are fairly straightforward. The traditional visual model of the atom (although not entirely accurate) consists of a nucleus made up of protons and neutrons, and electrons orbiting on the outside. In reality the atom is mostly empty space; it could never be illustrated to scale on a single sheet of paper or a computer screen. If we drew the atom to scale, with protons and neutrons a centimeter in diameter, it would take more than 30 football fields to draw out its total diameter. Atoms are 99.99 % just empty space. If that is the case, why don’t we walk right through walls or fall through the floor? This is due to the atom’s electrical charges. We don’t fall through the floor because the electrically charged atoms of the floor repel the electrically charged atoms of our feet. When we walk across the floor we are not actually touching the floor, but levitating at a height of a hundred millionth of a centimeter.
Now let’s get back to the structure of the atom. The electrons and quarks are believed to be the irreducible elementary particles that make up the atom. Quarks are grouped together in the nucleus to form protons and neutrons. Electrons whiz around the nucleus, not like orbits as the tradition model portrays, but more like a cloud of electrons that simultaneously occupy every possible location. Protons and electrons carry opposite electrical charges, which are arbitrarily called positive and negative—protons have a positive charge, and electrons have a negative charge.
The number of protons determines an atom’s chemical identity. Hydrogen, which contains only one proton, is the simplest element. Helium has two protons, lithium three protons, and so on. Every time you add a proton, you get a new element, up to about one hundred that are listed in the periodic table. The number of electrons is equal to the number of protons. This means that generally an atom has no net charge, because the positive and negative charges cancel out. However, certain atoms can lose or gain electrons, and acquire a charge—either positive or negative. This is called an ion. Neutrons have no charge, but they contribute to the atom’s mass. The mass of a neutron is equal to the mass of a proton. What’s more, although neutrons share the nucleus with protons, they don’t influence an atom’s chemical identity. Similar to electrons, the number of neutrons is usually the same as protons, but not always. They can vary, either more or less. In a nutshell, that’s the basic structure of the atom.
When two or more atoms are joined in a stable arrangement, you get a molecule. A molecule may consist of atoms of a single chemical element, such as two atoms of oxygen. Or it may also consist of different elements, such as a water molecule (H2O), which is made up of two hydrogen atoms and one oxygen atom. Although everything is made up of atoms, an element is the simplest arrangement, which cannot be split by chemical means. A compound consists of two or more different elements that are held together by chemical bonds. Therefore, water is a compound, composed of two elements, which are hydrogen and oxygen.
Another point worth noting is that there is no fundamental difference from one like subatomic particle to another. Every proton is exactly the same, irrespective of the element it is a part of. A proton in a hydrogen atom is identical to a proton in an oxygen atom or a helium atom. The same is true for neutrons and electrons.
Atoms are extremely small, abundant, durable, versatile and useful. It is difficult to get an idea of the scale of atoms. Numbers alone cannot really convey what’s going on down there, but I will give it a try anyway. Let’s start with size. If you examine the metric scale on an ordinary ruler, you will typically see numbers that mark out thirty centimeters. Each centimeter will also be divided in ten increments (those are millimeters). Take one millimeter and divide it into one thousand equal lengths, and you have microns. Now you are down to the scale of microorganisms, but you have not yet come close to the scale of atoms. To get down to the size of atoms you have to divide a micron into ten thousand equal lengths. Finally, you have reached your destination in inner space—the scale of atoms—one ten-millionth of a millimeter.
From our medium world perspective (somewhere in-between the universe’s large and small scales), this is an unimaginably small scale. Half a million atoms could hide behind the thickness of a human hair. And the size of an atom in relation to a millimeter is comparable to the thickness of a sheet of paper to the height of the Empire State Building. You may think we have reached the end of the line, but remember that atoms are made up of even more elementary particles. The nucleus is ten thousand times smaller than the whole atom, and electrons are at least ten thousand times smaller than the nucleus.
With some kind of idea how small atoms really are, there is virtually no point contemplating the actually number of atoms that exist—there are just too many. Atoms practically last forever; they circulate from place to place, and when something has outlived its usefulness, the atoms will reassemble to become part of something else. The atoms that make up you and me have been part of countless other living and nonliving things. Actually, this process of atomic reassembling is on-going. Even during our lifetime, the atoms in our body are continually being replaced by new ones—that is, new for us. Nevertheless, it all comes down to one basic realization. Everything is made from different arrangements of the same fundamental ingredients. Just take a look at the world around you. Even though things exhibit different properties, whether you are looking at water, air, wood, stone and metals—or plants, animals and people—it’s all made of the same stuff.
References: Bill Bryson, A Short History of Nearly Everything (London: Black Swan, 2004), 175.