Detailed decay information for the isotope iodine-127 including decay chains and daughter products. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element. The atomic mass is carried by the atomic nucleus, which occupies only about 10 -12 of the total volume of the atom or less, but it contains all the positive charge and at least 99.95% of the total. So, relative atomic mass means the mass of one atom is compared to the mass of another atom. The atom to which other atoms are compared to is usually called the standard. At present, an isotope of carbon called carbon-12 (C-12) is selected as the standard and assigned an atomic mass of exactly 12 amu, where amu stands for atomic mass units. The atomic mass is usually measured in the units unified atomic mass unit (u), or dalton (Da). Both units are derived from the carbon-12 isotope, as 12 u is the exact atomic mass of that isotope. So 1 u is 1/12 of the mass of a carbon-12 isotope: 1 u = 1 Da = m(12 C)/12.

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 of three isotopes: neon-20 (with 10 protons and 10 neutrons in its nucleus) with a mass of 19.992 amu and an abundance of 90.48%, neon-21 (with 10 protons and 11 neutrons) with a mass of 20.994 amu and an abundance of 0.27%, and neon-22 (with 10 protons and 12 neutrons) with a mass of 21.991 amu and an abundance of 9.25%. The average atomic mass of neon is thus: Puzzle quest for mac.

Atomic Mass Of Ice

0.9048	×	19.992 amu	=	18.09 amu
0.0027	×	20.994 amu	=	0.057 amu
0.0925	×	21.991 amu	=	2.03 amu
20.18 amu

The atomic mass is useful in chemistry when it is paired with the mole concept: the atomic mass of an element, measured in amu, is the same as the mass in grams of one mole of an element. Thus, since the atomic mass of iron is 55.847 amu, one mole of iron atoms would weigh 55.847 grams. The same concept can be extended to ionic compounds and molecules. One formula unit of sodium chloride (NaCl) would weigh 58.44 amu (22.98977 amu for Na + 35.453 amu for Cl), so a mole of sodium chloride would weigh 58.44 grams. One molecule of water (H₂O) would weigh 18.02 amu (2×1.00797 amu for H + 15.9994 amu for O), and a mole of water molecules would weigh 18.02 grams.

Atomic Mass Of Iron Element

The original periodic table of the elements published by Dimitri Mendeleev in 1869 arranged the elements that were known at the time in order of increasing atomic weight, since this was prior to the discovery of the nucleus and the interior structure of the atom. The modern periodic table is arranged in order of increasing atomic number instead.