An atom is the smallest particle of an element that retains the element's chemical identity; the word comes from the Greek 'atomos', meaning indivisible. Although atoms are in fact made of smaller subatomic particles, they are the basic units that take part in chemical reactions. Every element, such as hydrogen or carbon, is composed of its own characteristic atoms.

原子是仍保持元素化学特性的最小粒子;该词源自希腊语“atomos”,意为“不可分割”。虽然原子实际上由更小的亚原子粒子构成,但原子是参与化学反应的基本单元。每种元素(如氢或碳)都由其特有的原子构成。