Enter the percentage abundance and mass of up to 5 different isotopes into the average atom mass calculator. The calculator will display the average atomic mass of the isotopes.

• Atomic Mass Of Fe
• Atomic Mass Of Co2
• Atomic Mass Of Coal

Average Atomic Mass Formula

The total mass of these would be (23 x 10) + (100 x 11) = 1330. The average mass of these 123 atoms would be 1330 / 123 = 10.8 (to 3 significant figures). 10.8 is the relative atomic mass of boron. Notice the effect of the 'weighted' average. A simple average of 10 and 11 is, of course, 10.5. Atomic mass of Cobalt is 58.9332 u. The atomic mass is the mass of an atom. 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. CO (carbon monoxide) is a molecule, and therefore has a Gram Formula Mass, and not a Relative Atomic Mass. The GFM of CO is 28 = Carbon has a RAM of 12 and O has a RAM of 16.

The following formula is used to calculate the average atomic mass of a substance.

AM = f₁M₁ + f₂M₂ +… + f_nM_n

• Where AM is the average atomic mass
• fn is the fractional percent of the isotope
• M is the mass of the isotope

Atomic Mass Of Fe

Average Atomic Mass Definition

An average atomic mass is defined as the average mass of all isotopes within a given substance.

How to calculate average atomic mass?

How to calculate average atomic mass

1. First, determine the fractional percent of each isotope in the substance

   For example, chlorine has two major isotopes. 1 with 75.77 percent of atoms and 1 with 24.23 percent of atoms. These two percentages would be the fractional percents of those isotopes.

2. Next, determine the masses of each isotope

   Using the same example above, this would be 35 and 37 amu respectively.

3. Finally, calculate the average atomic mass

   Calculate the average atomic mass using the information from steps 1 and 2 and the formula above.

FAQ

The average atomic mass is the average mass of all of the isotopes that make up a substance.

The fractional percent is the total percentage a particular isotope in a substance.

Click a column header, such as Name, to sort the table by that item.
SEENotes at the bottom of the Table.

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Notes:
• Density of elements with boiling points below 0°C is given in g/l. In a sorted list, these elements are shown before other elements that have boiling points >0°C.
• Earth crust composition average values are from a report by F. W. Clarke and H. S. Washington, 1924. Elemental composition of crustal rocks differ between different localities (see article).
• Group: There are only 18 groups in the periodic table that constitute the columns of the table. Lanthanoids and Actinoids are numbered as 101 and 102 to separate them in sorting by group.
• The elements marked with an asterisk (in the 2nd column) have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Abbreviations and Definitions:

No. - Atomic Number; M.P. - melting point; B.P. - boiling point

Atomic number: The number of protons in an atom. Each element is uniquely defined by its atomic number.

Atomic mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. Atomic mass is measured in Atomic Mass Units (amu) which are scaled relative to carbon, ¹²C, that is taken as a standard element with an atomic mass of 12. This isotope of carbon has 6 protons and 6 neutrons. Thus, each proton and neutron has a mass of about 1 amu.

Isotope: Atoms of the same element with the same atomic number, but different number of neutrons. Isotope of an element is defined by the sum of the number of protons and neutrons in its nucleus. Elements have more than one isotope with varying numbers of neutrons. For example, there are two common isotopes of carbon, ¹²C and ¹³C which have 6 and 7 neutrons respectively. The abundances of different isotopes of elements vary in nature depending on the source of materials. For relative abundances of isotopes in nature see reference on Atomic Weights and Isotopic Compositions.

Atomic Mass Of Co2

Atomic weight: Atomic weight values represent weighted average of the masses of all naturally occurring isotopes of an element. The values shown here are based on the IUPAC Commission determinations (Pure Appl. Chem. 73:667-683, 2001). The elements marked with an asterisk have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Electron configuration: See next page for explanation of electron configuration of atoms.

Ionization energy (IE): The energy required to remove the outermost electron from an atom or a positive ion in its ground level. The table lists only the first IE in eV units. To convert to kJ/mol multiply by 96.4869. Reference: NIST Reference Table on Ground states and ionization energies for the neutral atoms. IE decreases going down a column of the periodic table, and increases from left to right in a row. Thus, alkali metals have the lowest IE in a period and Rare gases have the highest.

Atomic Mass Of Coal

Other resources related to the Periodic Table

• Chemical Evolution of the Universe