What is defined as a substance that cannot be broken down into simpler substances?

An element is defined as a fundamental substance that cannot be broken down into simpler substances through chemical reactions. Elements are the building blocks of matter and consist of only one type of atom. Each element has unique properties and is represented on the periodic table.

For example, hydrogen is an element that cannot be decomposed into simpler substances, and it consists solely of hydrogen atoms. This distinguishes elements from compounds, which are made up of two or more different elements chemically bonded together, and can be separated into simpler substances through chemical reactions. Mixtures, on the other hand, are combinations of two or more substances that retain their individual properties and can often be separated by physical means. Atoms are the smallest units of an element and can exist independently but are not substances themselves that can be defined as being broken down.