What is the difference between an element and a compound?

• A. An element is a substance made of only one type of atom; a compound is formed from two or more elements chemically bonded.
• B. An element is composed of molecules; a compound is a pure element.
• C. An element is a mixture; a compound is a pure substance.
• D. An element is always a solid; a compound is always a liquid.

Answer: (A)

Elements are pure substances made of only one type of atom. They can’t be broken down into simpler substances by chemical means, though they can exist as individual atoms or as molecules composed of the same atom (like O2 or N2). Compounds, on the other hand, are formed when two or more different elements bond chemically in a fixed ratio. The compound has properties different from its constituent elements and can be broken down into elements only through chemical reactions. For example, water results from hydrogen and oxygen combining in a 2:1 ratio and behaves very differently from either gas; table salt comes from sodium and chlorine combining, with its own distinct properties.