Final answer:
Elements are pure substances because they cannot be separated into simpler substances by physical means. They are made of a single type of atom and there are approximately 118 known elements, with some artificially created in laboratories.
Step-by-step explanation:
Elements are described as pure substances because they cannot be separated into parts by physical means. An element is a chemical substance that can't be divided or changed into other chemical substances by any ordinary chemical means. The smallest unit of an element is the atom. Elements comprise a single type of atom, and there are about 118 known elements, some of which were created in laboratories and do not occur naturally.
Pure substances can be either elements or compounds, with elements being unable to be broken down into simpler substances by chemical changes. For instance, aluminum, used in soda cans, is an element, while water is a compound made up of hydrogen and oxygen. The periodic table organizes elements by atomic number, reflecting the number of protons in the nucleus of their atoms.