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What Are Atoms?

An atom is the basic building block of each of the 118 different chemical elements on the periodic table. Atoms are often found in nature as groups of two or more atoms, called molecules, held together in different chemical ways, called bonds.

The Structure of Atoms

Atoms are made of even smaller components called subatomic particles, the term for all particles smaller than atoms. These include positively-charged protons, neutral neutrons, and negatively-charged electrons.

Protons and neutrons are found in the center of the atom, called the nucleus, while the electrons orbit around the nucleus. It's the number of protons in the nucleus of an atom that determines what element it is. For example, the nucleus of a hydrogen (H) atom has 1 proton, while a helium (He) atom has 2 protons.

Did you know?

  • The metal element gold can be hammered into a sheet that is 1 atom thick.

    Gold is a very malleable and ductile metal, meaning it can be hammered or stretched into thin sheets or wires. In fact, gold is so malleable that it can be beaten into sheets that are as thin as a single atom, which is about 0.3 nm (nanometers, or billionths of a meter) thick! These ultra-thin sheets of gold, called "monolayers," have unique optical and electronic properties that make them useful in a variety of applications, from electronics to medical devices.

  • Atoms can actually be seen through certain ultra-powerful microscopes.

    Scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) are two types of instruments that allow scientists to "see" individual atoms and even manipulate them. These microscopes work by scanning a tiny probe over the surface of a sample and measuring the interactions between the probe and the atoms. By creating a 3D map of the interactions, scientists can create images of the surface with incredibly high resolution, sometimes even showing individual atoms.

  • The sizes of atoms are measured in billionths of a meter.

    Atoms are incredibly small, with a diameters measuring from 0.1 to 0.5 nm (nanometers, or billionths of a meter). To put that into perspective, a single strand of human hair is about 100,000 nm wide, which means you could fit anywhere from 200,000 to 1 million atoms side by side on the width of a single strand of hair!

  • The atoms in our bodies and around us likely came from stars that exploded billions of years ago.

    The atoms in the elements that make up our bodies, such as carbon, oxygen, and iron, were formed in the hearts of massive stars that eventually exploded as supernovae. The intense heat and pressure of these explosions caused elements like hydrogen and helium to fuse together into heavier elements, which were then scattered into space. Over time, these elements eventually formed new stars and planets, including Earth.

  • The average adult human body contains octillions of atoms.

    While the number of atoms can vary greatly depending on a person's size, weight, and body composition, scientists have estimated that an average adult human body is made up of roughly 7 octillion (7 x 10^27), or 7 billion billion billion atoms. The vast majority of these atoms are hydrogen, oxygen, and carbon atoms, which are the primary building blocks of organic molecules such as proteins, carbohydrates, and fats.

  • Atoms are more than 99.9% empty space.

    Put another way, if you were to magnify an atom to the size of a sports stadium, the nucleus would only be about the size of a pea! It's only because these particles are so small and so tightly packed together that we perceive them as solid objects.