Atoms

Atoms are the basic building blocks of all ordinary matter. Everything around us, including air, water, rocks, plants and living organisms, is made of atoms. An atom is extremely small, measuring about one ten-billionth of a meter across. Each atom has a central nucleus containing positively charged protons and electrically neutral neutrons.

Around the nucleus move negatively charged electrons, which occupy regions called orbitals rather than following fixed paths. The number of protons determines which chemical element an atom belongs to. For example, every hydrogen atom has one proton, while every carbon atom has six. Atoms of the same element can contain different numbers of neutrons; these forms are known as isotopes.

Most atoms are stable, but some are naturally radioactive because their nuclei change over time. Atoms rarely exist alone in nature. Instead, they usually bond with other atoms to form molecules and larger structures. Water is made of two hydrogen atoms bonded to one oxygen atom, while common table salt is formed from sodium and chlorine atoms arranged in a repeating crystal structure.

Chemical reactions occur when atoms rearrange their bonds without changing the nuclei themselves. Although atoms are too small to be seen with ordinary microscopes, scientists can study them using advanced instruments and experiments. Understanding atoms has made it possible to develop new materials, medicines, electronic devices and many technologies used in everyday life.