Element vs Compound

Quick Answer

An element contains only one type of atom. A compound contains two or more different elements chemically bonded in a fixed ratio.

What Each One Really Means

This one is basic, but I include it here because I still see it confuse people in advanced classes. An element is the simplest kind of matter that cannot be broken down by chemical means. It contains only one type of atom. Gold is an element. Oxygen is an element. Sodium is an element. That is it. A compound is a substance formed when two or more different elements chemically bond together in a fixed ratio. Water is a compound. Sodium chloride is a compound. Carbon dioxide is a compound. Notice the phrase 'fixed ratio'. This is important. Water is always two hydrogen atoms to one oxygen atom. Not approximately. Exactly. If you change the ratio, you get a different compound, like hydrogen peroxide, which is two hydrogens to two oxygens. Same elements, different compound. Now here is the subtle point that trips students up. A mixture is not a compound. In a mixture, the substances are not chemically bonded, and the ratio can vary. Air is a mixture, not a compound. Salt water is a mixture. The test is simple. Can you separate it by physical means? If yes, it is a mixture. If no, and the ratio is fixed, it is a compound. And please, do not confuse an element with an atom. An element is a substance. An atom is the smallest particle of that substance. Different levels of description. Same idea, different scale.

Side-by-Side Comparison

Memory Device

Element is one type of atom. Compound is more than one type, bonded in a fixed ratio.

Related Topics