Final answer:
An atom is the smallest particle of an element that retains its distinctive characteristics. Atoms are incredibly small, with sizes of about 100 picometers, and make up all forms of matter. They maintain the element's properties and can combine to form molecules.
Step-by-step explanation:
The smallest particle of an element that retains the characteristics of that element is an atom. Atoms are fundamental units of matter and are composed of a nucleus made of protons and neutrons, surrounded by a cloud of electrons. The concept of the atom is derived from the ancient Greek word atomos, meaning 'indivisible', suggesting that atoms are the smallest components that retain the identity and properties of an element.
Atoms are extremely small, with typical sizes around 100 picometers (1×10-10 m). To visualize this, around fifty million atoms placed side by side would span only 1 cm. Every solid, liquid, gas, and plasma is composed of these atoms, which may be neutral or ionized. Their small size and the effects of quantum mechanics make atoms difficult to observe with conventional microscopes, and their behavior is not accurately predicted by classical physics.
The unique chemical properties of an element are due to its atomic structure. If an atom were divided further, such that the subatomic particles were separated, it would no longer maintain the properties of the original element. Atoms can also combine to form molecules, which are groups of atoms bonded together, representing the smallest fundamental units of a chemical compound.