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You are here: Home / Class 9 / Atoms and Molecules / Atomic Mass

Atomic Mass

Last Updated on August 21, 2020 By Mrs Shilpi Nagpal Leave a Comment

Question 1 How is the size of an atom indicated?

Question 2 Define atomic mass unit?

Question 3 What is the mass of hydrogen atom?

Question 4 Name the element used as a standard for atomic mass scale?

Atomic Mass of an Element

Actual masses of the atoms of the elements are very very small.

For Example : The atom of hydrogen has a mass of 1.6727 x 10-27 kg. It is not convenient to use such small and complicated figures in our calculation,therefore ,it was necessary to define atomic masses in such a way that we get simple figures for them.

Carbon-12 is that atom of carbon which has 6 protons and 6 neutrons in its nucleus so that so its mass number is 12.

carbon-12 atom has been assigned an atomic mass of exactly 12 atomic mass units.This means that a carbon-12 atom has been assigned an atomic mass of exactly 12u.

Atomic Mass unit = the mass of a carbon – 12 atom

Atomic mass unit
One Atomic Unit is defined as exactly one-twelfth the mass of an atom of carbon-12.

Carbon-12 atom is taken to be the standard.The atomic masses of all other elements are determined by comparing the mass of their atom with the mass of a carbon-12 atom.

The atomic mass of an element is relative mass of its atom as compared with the mass of a carbon-12 atom taken as 12 units.

Filed Under: Atoms and Molecules, Class 9 Tagged With: atomic mass of element, atomic mass unit, carbon-12, mass of hydrogen, one atomic unit

About Mrs Shilpi Nagpal

Author of this website, Mrs Shilpi Nagpal is MSc (Hons, Chemistry) and BSc (Hons, Chemistry) from Delhi University, B.Ed (I. P. University) and has many years of experience in teaching. She has started this educational website with the mindset of spreading Free Education to everyone.

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