Everything you see, touch, and breathe is made up of incredibly small pieces, much tinier than a grain of sand or a speck of dust. These tiny, invisible pieces are called atoms, and they are the fundamental building blocks of all matter in the universe. Imagine them as the world’s most microscopic set of construction bricks, constantly joining together in countless ways to create everything from the air around you to the planet beneath your feet. Understanding atoms is the first step in understanding science, because they determine the properties and behavior of every material we encounter.
The Tiny Building Blocks
Atoms are so small that you cannot see them with a regular classroom microscope; they are thousands of times smaller than the width of a human hair. To put their size into perspective, a single human hair is about a million carbon atoms wide. If you were to line up roughly 50 million atoms, the resulting row would measure only about half an inch.
Because of their minuscule size, scientists must use specialized tools like a scanning tunneling microscope to capture images of atoms. The word “atom” comes from the ancient Greek word, atomos, meaning “uncuttable” or “indivisible.” Atoms are the smallest unit of an element that retains its chemical identity.
Each different kind of atom makes up a specific chemical element, like hydrogen, oxygen, or gold. There are currently 118 known types of atoms, and each type is unique due to the specific number of pieces it contains. The atoms of different elements have unique properties, which is why a diamond, made of carbon atoms, is hard, and the oxygen you breathe is a gas.
What Is Inside an Atom
Atoms are made up of three even tinier particles, called subatomic particles: protons, neutrons, and electrons. The atom is organized with a dense center and particles moving around it.
The center of the atom is called the nucleus, and it contains the heaviest particles: protons and neutrons. Protons carry a positive electrical charge, and they are what determine the atom’s identity. For example, every atom with six protons is a carbon atom, and every atom with eight protons is an oxygen atom.
Neutrons are also found in the nucleus, but they are neutral, meaning they have no electrical charge. Protons and neutrons are comparable in size and together make up almost the entire mass of the atom. The nucleus is incredibly small and dense, taking up less than one-ten-thousandth of the atom’s total volume, similar to a marble in the middle of a football field.
The third particle is the electron, which has a negative electrical charge. Electrons are much lighter than protons and neutrons, being approximately 1,800 times smaller. They move at incredible speeds in a cloud-like region far outside the nucleus. The opposite charges of the protons and electrons create a strong electromagnetic attraction that keeps the electrons bound to the nucleus.
Atoms Make Up Everything
Atoms join together to form molecules. A molecule is created when two or more atoms connect in a specific arrangement, like tiny LEGO bricks locking together. For instance, a water molecule is always made of two hydrogen atoms and one oxygen atom, which is why its scientific formula is written as H₂O.
Atoms connect by sharing or exchanging their outermost electrons, which forms chemical bonds. The way atoms connect dictates the properties of the resulting molecule. For example, molecules in a solid like ice are packed tightly together, while molecules in a gas like helium fly around freely.
Every object—the screen you are reading this on, the air you breathe, the food you eat—is simply a different combination of atoms and molecules. The different ratios of atoms create different substances; for instance, six carbon atoms, twelve hydrogen atoms, and six oxygen atoms combine to create a single sugar molecule. This ability of atoms to link up makes them the universal construction set, forming everything in the world.