Final answer:
A substance made up of only one type of atom is called an element, of which there are 118 known on the Periodic Table, each with unique properties.
Step-by-step explanation:
Elements, the fundamental constituents of matter, are composed of a single type of atom and serve as the elemental building blocks of the universe. The Periodic Table of the Elements catalogues 118 confirmed elements, each uniquely defined by its proton count and distinct properties. These properties, including melting point and color, remain constant across all pure samples of the element.
The astounding unity of the universe arises from the combination and arrangement of these elements, showcasing their pivotal role in constructing diverse materials. For example, aluminum, an element widely used in beverage cans, possesses specific properties that endure consistently in any pure form. This foundational concept underpins the classification and understanding of the vast array of substances encountered in our everyday surroundings.