The ancient Greeks believed that everything in the universe was composed of water, fire, earth and air, which was called the "four elements theory". Two light elements, fire and air, will float, two heavy elements, soil and water, will sink, and four elements will form various objects in a certain proportion. China had a similar view in ancient times. Our ancestors believed that everything in the universe was made up of gold, wood, water, fire and earth.

This is the wrong definition.

Chemically, it is the general name of the same kind of atoms with the same proton number (nuclear charge number).

Elements refer to more than 100 kinds of basic metallic and nonmetallic substances in nature. They are only composed of several atoms with the same characteristics. Each nucleus of an atom has the same number of protons, which cannot be made simpler by general chemical methods. All substances are composed alone or in combination. It is the abbreviation of chemical element.

Mathematically speaking, an element is an element and everything that makes up a set.

The branch of mathematics that studies the operations and properties of sets is called set theory or set theory. The definition of set is very broad, not limited to mathematics, but also widely used in production and life. All things with specific attributes that make up a specific set can be called elements. So the definition of elements is also very broad.