Atoms are the basic building blocks of every materials or substances. It is very small in size and are not visible in naked eyes. Can we measure the size and mass of an atom? Yes we can. The mass of the atom is termed as **Atomic Mass**. We know that most of this mass of the atom is concentrated in the nucleus as the electrons have negligible mass. The Nucleus is made up of protons and neutrons.Thus we can say the atomic mass is the mass of protons and neutrons present in the nucleus.

Consider a Carbon atom it contains 6 protons and 6 neutrons. Hence it has the atomic mass as 12.

Taking this element as standard we express the atomic mass of any in**amu**.

Where, 1 amu = $\frac{1}{12}$ th the mass of carbon atom. The atomic mass unit is represented as**'u'**.

1 u = $\frac{Mass of ^{12}C_{6} atom}{12}$

The**Average Atomic Mass** is the average of all the atoms present in the element. Let us study the concepts lying behind the average atomic mass in detail.

Consider a Carbon atom it contains 6 protons and 6 neutrons. Hence it has the atomic mass as 12.

Taking this element as standard we express the atomic mass of any in

Where, 1 amu = $\frac{1}{12}$ th the mass of carbon atom. The atomic mass unit is represented as

1 u = $\frac{Mass of ^{12}C_{6} atom}{12}$

The

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Atomic mass is the total matter present in one atom of an element. All atoms consist of three subatomic particles namely :

Thus, the**Atomic Mass** of an atom is defined as the total number of protons and neutrons present in the nucleus of that atom. The atomic mass is represented by the symbol **A** and is measured in **amu** (atomic mass unit).An atomic mass unit (amu) is equal to the mass of 1/12th the mass of a carbon atom of the isotope C-12.

The** Average Atomic Mass** is the average of the
atomic mass of all the isotopes of the element. There are several
elements which has number of naturally isotopes.

**Protons****Electrons****Neutrons**

Thus, the

The

Atomic mass |
Average atomic mass |

It is the total mass of neutrons, Protons and electrons. | It is average mixture of the isotopes of the element. |

It is obtained directly from the periodic table. | It is the obtained by calculating percent abundance of each isotope and their atomic mass. |

It is an individual mass of the measure of each isotope. | Average of the atomic mass when all the naturally occurring isotopes of the elements are mixed in a proportion. |

The **Average Atomic Mass** is the weighted average of each isotope of an element.

Lets take an example of an element**'Y'** which has isotopes **Y**_{1}, Y_{2}......Y_{n} then
its average atomic mass is given by :

Lets take an example of an element

Average Atomic Mass **(Y)** = (Atomic Mass of Y_{1}) $\times$ $\frac{Y_{1}}{100}$ + (Atomic Mass Y_{2}) $\frac{Y_{2}}{100}$ +.......+ (Atomic mass Y_{n}) $\frac{Y_{n}}{100}$.It is expressed in **Atomic Mass Unit (amu)**.

The Average atomic mass is the weighted sum of all the isotopes of the
element. The Average atomic mass is given by formula:

Average Atomic Mass**(Y)** = (Atomic Mass Y_{1}) $\times$ $\frac{Y_{1}}{100}$ + (Atomic Mass Y_{2}) $\frac{Y_{2}}{100}$ +.........Where,

**Y**_{1} % = Percent Abundance of Y_{1}

**
Y**_{2} % = Percent Abundance of Y_{2}.

For finding the average atomic mass of an element it is necessary to determine the number of the naturally occurring isotopes of that element and also their percent abundance in the nature.

Average Atomic Mass

For finding the average atomic mass of an element it is necessary to determine the number of the naturally occurring isotopes of that element and also their percent abundance in the nature.

The **Percent Abundance** is the percentage amount of all the natural
occurring isotopes of the element.

It is used to find the average atomic mass of the element.

As we know that the isotopes of each element occurs in different ratios and hence the percent abundance signifies the percentage of finding the isotope of the element while mining that element, since each element may contain a mixture of the isotopes.

It is used to find the average atomic mass of the element.

As we know that the isotopes of each element occurs in different ratios and hence the percent abundance signifies the percentage of finding the isotope of the element while mining that element, since each element may contain a mixture of the isotopes.

Average Atomic Mass is given by the formula:

**Average atomic mass= $\sum$ (Mass of isotope $\times$ Percentage isotope abundance)**If the element **Y** has **Y**_{1}, Y_{2}, Y_{3} ......... Y_{n} number of elements then for Calculating Average Atomic Mass, the percent abundance of each isotope
and atomic mass of each isotope is obtained and then by using the
following formula:

Average Atomic Mass**(Y)** = (Atomic mass Y_{1}) $\frac{Y_{1}}{100}$ + (Atomic mass Y_{2}) $\times$ $\frac{Y_{2}}{100}$ +....… (Atomic mass Y_{n}) $\frac{Y_{n}}{100}$.Where

$\frac{Y_{1}}{100}$= Percent Abundance of**Y**_{1}

$\frac{Y_{2}}{100}$ = Percent Abundance of**Y**_{2}.

Now we will solve some problems of finding the average atomic mass to understand it better.

Average Atomic Mass

$\frac{Y_{1}}{100}$= Percent Abundance of

$\frac{Y_{2}}{100}$ = Percent Abundance of

Now we will solve some problems of finding the average atomic mass to understand it better.

By using the following formula we can find the average atomic mass of rubidium,

Average atomic mass= $\sum$ (Mass of Isotope $\times$ Percent abundance)

Average atomic mass = 85 $\times$ $\frac{72.2}{100}$ + 87 $\times$ $\frac{27.8}{100}$.

Average atomic mass = 61.37 amu + 24.186 amu.

Average atomic mass = 85.556 amu

The Average atomic mass of the rubidium is

- 46 Ti (8.0%)
- 47 Ti (7.8%)
- 48 Ti (73.4%)
- 49 Ti (5.5%)
- 50 Ti (5.3%).

The Average atomic mass of titanium is obtained by using the following formula:

Average atomic mass= $\sum$ (mass of isotope $\times$ Percent abundance).

Average atomic mass=46 $\times$ $\frac{8}{100}$ + 47 $\times$ $\frac{7.8}{100}$ + 48 $\times$ $\frac{73.4}{100}$ + 49 $\times$ $\frac{5.5}{100}$ + 50 $\times$ $\frac{5.3}{100}$.

Average atomic mass = (3.68 + 3.666 + 35.232 + 2.695 + 2.65) amu.

Average atomic mass = 47.932 amu.

The Average atomic mass of the titanium is

The Average atomic mass of chlorine is obtained by using the following formula:

Average atomic mass= $\sum$ (Mass of isotope $\times$ Percent abundance)

Average atomic mass=34.969 $\times$ $\frac{75.53}{100}$ + 36.966 $\times$ $\frac{24.47}{100}$.

Average atomic mass = 26.412 amu + 9.045 amu

Average atomic mass = 35.457 amu.

The Average atomic mass of the chlorine is

The atomic mass of 24Mg is obtained by using the following formula:

Average atomic mass = $\sum$ (Mass of isotope $\times$ Percent abundance) 24.3050

= X $\frac{78.7}{100}$ + 24.98584 $\times$ $\frac{10.13}{100}$ + 25.98259 $\times$ $\frac{11.7}{100}$.

X = 23.98504 amu.

The atomic mass of 24Mg is 23.98504 amu.

The Average atomic mass of uranium is obtained by using the following formula:

Average atomic mass = $\sum$ mass of isotope $\times$ Percent abundance.

Average atomic mass = 234 $\times$ $\frac{0.01}{100}$ + 235 $\times$ $\frac{0.71}{100}$ + 238 $\times$ $\frac{99.28}{100}$.

Average atomic mass = 0.0234 amu + 1.6685 amu + 236.2864 amu.

Average atomic mass = 237.9783 amu.

The Average atomic mass of the uranium is

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