Atomic Masses – Class 12 | Chapter – 13 | Physics Short Notes Series PDF for NEET & JEE

Atomic Masses: Atomic mass refers to the mass of an atom, which is typically expressed in atomic mass units (amu). One atomic mass unit is defined as one-twelfth the mass of a carbon-12 atom, which has six protons and six neutrons in its nucleus.

The atomic mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. The number of protons determines the element that the atom belongs to, while the number of neutrons can vary within a particular element, resulting in different isotopes of the same element. For example, carbon-12 and carbon-13 are both isotopes of carbon, with different numbers of neutrons in their nuclei.

The atomic mass of an element is typically represented as a weighted average of the atomic masses of its isotopes, taking into account the abundance of each isotope in nature. This is called the atomic mass of the element. For example, the atomic mass of carbon is 12.011 amu, which is the weighted average of the masses of its two isotopes, carbon-12 and carbon-13, with their respective natural abundances.

Importance of Atomic Masses

Atomic masses are important in a number of fields, including chemistry, physics, and engineering. Some of the key reasons why atomic masses are important include:

  • Chemical reactions: Atomic masses are used to calculate the amounts of reactants and products in chemical reactions. This information is critical for designing and optimizing chemical processes and for understanding how chemical reactions occur.
  • Nuclear reactions: Atomic masses play a key role in understanding and predicting nuclear reactions, such as radioactive decay, fusion, and fission. The energy released in these reactions is directly related to the changes in the atomic masses of the particles involved.
  • Material science: Atomic masses are used to understand and predict the properties of new materials. By understanding the atomic structure and composition of a material, researchers can predict its behavior under different conditions and optimize its performance for specific applications.
  • Astrophysics: Atomic masses play a critical role in understanding the properties and behavior of stars and other celestial objects. By measuring the masses of stars and their constituent elements, researchers can gain insights into the processes that govern the formation and evolution of the universe.
  • Nuclear engineering: Atomic masses are important in the design and operation of nuclear reactors, which rely on nuclear reactions to produce energy. By understanding the atomic masses of the materials involved in these reactions, engineers can optimize the efficiency and safety of nuclear reactors.

Atomic Mass of First 30 Elements

The Atomic mass of some elements is tabulated below.

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

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By Team Learning Mantras