An atom is the fundamental building block of all matter. It is the smallest unit of a chemical element that still retains all the properties of that element. Every atom consists of a central nucleus containing protons and neutrons, surrounded by electrons orbiting in shells.
The atomic structure consists of three main components. The nucleus at the center contains protons, which carry a positive electric charge, and neutrons, which have no electric charge. Surrounding the nucleus are electrons, which carry a negative charge and move in orbital paths around the nucleus.
Atoms are extraordinarily small. Their diameter is approximately 0.1 nanometers, which is one ten-billionth of a meter. To put this in perspective, about 10 million atoms could fit across the tip of a pencil. Despite their tiny size, atoms contain even smaller particles - the nucleus is thousands of times smaller than the atom itself.
What makes one element different from another is the number of protons in its nucleus. Hydrogen, the simplest element, has just one proton and one electron. Carbon has six protons, six neutrons, and six electrons. This number of protons, called the atomic number, uniquely identifies each element and determines its chemical properties.
Atoms are truly everywhere in our daily lives. The water we drink is made of hydrogen and oxygen atoms. The air we breathe contains nitrogen and oxygen atoms. Our own bodies are composed of carbon, calcium, iron, and many other types of atoms. Understanding atoms helps us understand the fundamental nature of everything around us, from the smallest molecules to the largest structures in our world.