# Molecule --- A **molecule** is a group of [[atom|atoms]] that are [[chemical bond|bound]] together into one fundamental unit. The bonds between molecules can be [[covalent bond|covalent]] or [[ionic bond|ionic]]. Many molecules are also defined as [[substance|chemical compounds]], but the definition of molecule allows two or more atoms of the same [[element]] to be bound together, such as with [[oxygen]] (O$_2$). ## Molecular Color Conventions Atoms are smaller than the smallest wavelength of [[electromagnetic spectrum|visable light]], so we cannot technically "see" an atom, nor does it have a color. However, by convention there is a generally consistent color coordination used to visualize molecules. - **Carbon** is colored black because it’s the color of charcoal. - **Oxygen** is red because it’s necessary for combustion. - **Nitrogen** is blue because it’s the most abundant element in the Earth’s atmosphere and the sky appears blue. - **Hydrogen** is white because it forms a colorless gas. - **Chlorine** is green because it forms a greenish gas. - **Sulfur** is yellow because that’s its color in mineral form. - **Phosphorus** is orange because it glows orange in a flame. - **Iron** is reddish brown because it rusts ___