International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is the definition of an atom?

1. The smallest part of a molecule

2. The smallest part of an element

3. A collection of protons and neutrons

4. A charged particle

The correct answer is: The smallest part of an element

An atom is defined as the smallest part of an element that retains the chemical properties of that element. This means that while atoms can combine to form molecules, an individual atom still embodies the characteristics that define its element, such as its atomic number and specific chemical behavior. Each element is composed of atoms that have unique numbers of protons, which determines the type of element it is. Understanding this definition is crucial for grasping the foundational concepts of chemistry, as it establishes the basic building blocks from which all matter is composed. The other choices provided do not accurately capture the essence of an atom. For instance, referring to an atom as the smallest part of a molecule is misleading, as molecules can consist of one or more atoms bonded together. A collection of protons and neutrons may describe a nucleus but doesn’t encompass the whole atom, which also includes electrons. Lastly, defining an atom as a charged particle is inaccurate, as atoms are typically electrically neutral due to the balance of their protons and electrons, although they can gain or lose electrons to become ions. Thus, the definition of an atom as the smallest part of an element is both precise and critical to the study of chemistry.