What Is an Atom?

Full transcript

Everything around you — the water you drink, the air you breathe, even your own body — is made of matter, and all matter is built from incredibly tiny building blocks called atoms. If we could zoom deep inside a single drop of water, we would find tiny molecules — each one made of two hydrogen atoms bonded to one oxygen atom, forming the familiar H2O structure. Now let's zoom in even further and isolate just one of those atoms — a single oxygen atom — sitting alone so we can examine its inner structure in detail. At the very center of every atom is a dense core called the nucleus, which is packed tightly with positively charged particles called protons and neutral particles called neutrons. Surrounding the nucleus, tiny negatively charged particles called electrons orbit at a vast distance relative to the nucleus — making atoms almost entirely empty space, like a miniature solar system. But that neat planetary picture is actually a simplification — in reality, electrons don't follow fixed paths; instead they exist as a fuzzy cloud of probability, more likely to be found in certain regions than others. Here is the most important rule in all of chemistry: the number of protons inside the nucleus determines exactly which chemical element an atom is — change that number and you change the element entirely.