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Average Atomic Mass Calculator

Enter the percentage and masses for the number of isotops selected and the calculator will show complete work for average atomic mass.

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The average atomic mass calculator helps to calculate the average atomic mass based on the isotopic masses relative to their natural abundance in a sample substance.

What is Average Atomic Mass?

“The average atomic mass of an atom is the weighted average of all the isotopes present in a sample” The average atomic mass is also known to be the average atomic weight of an element. The main reason for finding the average atomic mass of an element is that elements have different atomic masses but the same atomic number.

Examples:

  • Hydrogen has three isotopes tritium, deuterium, and Protium
  • Carbon has three isotopes C-12,C-13, C-14
  • Oxygen has three isotopes O-16, O-17, O-18
You need to calculate the average atomic mass of the elements to know their atomic masses. This is the main reason the atomic numbers are always in a whole number while the atomic masses are in the form of decimals. If you are wondering how to calculate the average atomic mass of an element just use our average mass calculator.

How to Find the Average Atomic Mass?

Consider the three isotopes of oxygen-16, oxygen-17, and oxygen-18. Their relative atomic masses are 16 amu, 17amu, and 18 amu, respectively. The atomic number of oxygen is 8, which means that every oxygen atom has 8 protons, so the number of protons is fixed in the oxygen, but the number of neutrons is 8, 9, and 10 in the three isotopes respectively. The average atomic mass calculator calculates the average atomic mass based on the isotopic masses relative to their natural abundance in a sample substance. Now to find the average atomic mass of the oxygen, you need to add all the isotopes' atomic masses and their relative percentage.

Given:

Natural abundance of nth isotope (f) = 90 % , 8 %, 2 % Atomic mass of nth isotope (m) = 16 amu, 17amu, 18 amu

Solution:

When Natural abundance (f) values as a percentage, then divide by 100. The average atomic mass formula: Average Atomic Mass = (f1m1 + f2m2 + f3m3 ... + fnmn) / 100 Now to calculate the average atomic mass of oxygen, first multiply the percentage of the abundance by the atomic masses. Then divide it by 100 to calculate the average atomic mass of oxygen of all three isotopes. The average atomic mass calculator calculates the average atomic mass based on the isotopic masses relative to their natural abundance in a sample substance. Average Atomic Mass of Oxygen = [ (90 x 16) + (8 x 17) + (2 x 18) ] / 100 It is essential to calculate average atomic mass of the substance to know the natural abundance of the element's isotopes. The average atomic mass of oxygen is 16.12 amu  Average Atomic Mass of Oxygen= 16.12 amu The online average atomic mass calculator calculate average atomic mass element based on the masses of its isotopes and their natural abundance.

Average Atomic Masses Table:

The average atomic mass of an element is the average mass of all the isotopes of an element. Calculating average atomic mass of the elements is simple, if you learn what is the concept of the isotopes. In the table below the average atomic masses of the first 30 elements are given:
ATOMIC NUMBER ELEMENT ATOMIC MASS
1 Hydrogen 1.008
2 Helium 4.0026
3 Lithium 6.94
4 Beryllium 9.0122
5 Boron 10.81
6 Carbon 12.011
7 Nitrogen 14.007
8 Oxygen 15.999
9 Fluorine 18.998
10 Neon 20.180
11 Sodium 22.990
12 Magnesium 24.305
13 Aluminium 26.982
14 Silicon 28.085
15 Phosphorus 30.974
16 Sulfur 32.06
17 Chlorine 35.45
18 Argon 39.948
19 Potassium 39.098
20 Calcium 40.078
21 Scandium 44.956
22 Titanium 47.867
23 Vanadium 50.942
24 Chromium 51.996
25 Manganese 54.938
26 Iron 55.845
27 Cobalt 58.933
28 Nickel 58.693
29 Copper 63.546
30 Zinc 65.38

Average Atomic Mass Calculator Working:

Our tool is simple to use and you need only a couple of steps to find the average atomic mass of an element. Let's see how? Input:
  • Select the number of isotopes
  • Enter the percentage and the mass of all the isotopes
  • Tap calculate 
Output:
  • Average atomic mass 
  • Step-by-step calculation 

FAQs:

What are Isotopes?

Isotopes of an element have the same number of the proton, but different numbers of neutrons. For calculating average atomic mass, you need to take the average of all the isotopes' atomic weight relative to their percentage in the sample.

What is the Fractional Percentage?

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

References:

From the source of angelo.edu: Atomic masses, The isotopes From the source of getchemistryhelp.com: Atomic number, Example
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