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A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulae can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than chemical names and structural formulae. Al2(SO4)3 Aluminium sulfate has the chemical formula Al2(SO4)3. The form of aluminium sulfate hexadecahydrate is Al2(SO4)3·16H2O.   Structural formula for butane. Examples of other chemical

Atomic Masses 1A 2A 3A 4A 5A 6A 7A 8A (1) (2) (13) (14) (15) (16) (17) (18) 3B 4B 5B 6B 7B — 8B — 1B 2B (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) 1 H He 2 Li Be B C N O F Ne 3 Na Mg Al Si P S Cl Ar 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 Cs Ba La   Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac   Rf Db Sg Bh Hs Mt Ds Rg Uub — Uuq — — — — 6   Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 7   Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr   The  atomic mass  of an element is the average mass of the atoms of an element measured in  atomic mass unit  (amu, also known as  daltons , D).  The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.  (Atomic mass is also referred to as  atomic weight , but the term "mass" is more accurate.) For instance, it can be determined experimentally that neon consists