What is an atom?

• A. A subatomic particle with a negative charge.
• B. The fundamental unit of matter that composes all matter.
• C. A molecule made of two atoms.
• D. A type of energy.

Answer: (B)

An atom is the fundamental unit of matter that makes up everything around us. It is the smallest unit of an element that still has the element’s properties. At the center is the nucleus, containing positively charged protons and neutral neutrons. This nucleus is surrounded by a cloud of electrons, which are much lighter and negatively charged, held in orbit by the attraction to the nucleus. The overall atom is mostly empty space, with a tiny, dense nucleus. Atoms combine with other atoms to form molecules, and molecules build all substances we encounter. An atom is not a single subatomic particle like an electron, nor is it a molecule, nor is it a form of energy.