<P> Effective molecular radius is the size a molecule displays in solution . The table of permselectivity for different substances contains examples . </P> <P> The chemical formula for a molecule uses one line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (−) signs . These are limited to one typographic line of symbols, which may include subscripts and superscripts . </P> <P> A compound's empirical formula is a very simple type of chemical formula . It is the simplest integer ratio of the chemical elements that constitute it . For example, water is always composed of a 2: 1 ratio of hydrogen to oxygen atoms, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2: 6: 1 ratio . However, this does not determine the kind of molecule uniquely--dimethyl ether has the same ratios as ethanol, for instance . Molecules with the same atoms in different arrangements are called isomers . Also carbohydrates, for example, have the same ratio (carbon: hydrogen: oxygen = 1: 2: 1) (and thus the same empirical formula) but different total numbers of atoms in the molecule . </P> <P> The molecular formula reflects the exact number of atoms that compose the molecule and so characterizes different molecules . However different isomers can have the same atomic composition while being different molecules . </P>

What is the name for a large molecule made up of many small units