Home Education What is Atomic Mass | Mass of all atoms

What is Atomic Mass | Mass of all atoms


Basically atomic mass is depends on the total number of protons, neutron and electrons of an atom.

An atom consist of three basic particles – proton, neutron and electron. The nucleus (center) of the atom contains proton and neutron which have charges respectively Positive (+) and neutral (no charge) charge.

The outermost area of atom called electronic shell which contains electron which have negative (-) charge. I told you once that inner side of atom is like as

A solar system same electronic shell are the orbit where electron revolves around the nucleus in a fixed portion.

Size of all atoms are different it is depending on the sizes of electrons, protons and neutrons. Basically size of an average atom is about 1 × 10-10 m, a ten million of a millimeter, or 1/254,000,000 of an inch.

In models of atoms many specifications are presents.

Chemical and physical Scientists are trying to make new ones every day in their labs. They are making study of atoms easier day by day for student like us.

After the discovery of modern periodic table atomic number become more popular because the modern periodic table is completely based on the atomic number of any atom or element.

All atom are completely arranged systematic on the basis of atomic number. It is easy to learn it of an atom as compared to it’s mass.

But before the invention of modern periodic table atomic weight is the main component of the atom.

It is essential to know atomic weight of any atom because the periodic tables that made

In past’s periodic tables are completely based on the atomic weight of such element or atom.

Thinks that you are going to know in this article –

  1. What is atomic mass ?
  2. Isotopes and Isobars
  3. Discovery of atomic mass
  4. Conclusion
  5. FAQ

What is atomic mass ?

Inside of atom basically three things are present – electron which revolves around the nucleus of the atom and carries negative (-) charge,

And nucleus present in the center of atom which has positive charge,

Inside of nucleus it consist two things proton which carries positive charge (+) and neutron

Which carries no charge (0) and remain part of the atom is hollow.

Basically atomic weight of an atom is the total of numbers of proton or neutron in the nucleus of the atom.

Numerical values of atomic mass

Although the SI unit of weight is kilogram or kg, the atomic weight is often expressed in a non-SI unit called Dalton (Da or u) where 1 dalton means 1/12 of the mass of a single carbon 12 atom at reset.

Element Weight
Oxygen15.999 u
Carbon12.0107 u

The numerical value of the atomic mass when it expressed in Daltons has nearly the same value of the it as mass number.

Isotopes and Isobars

Atoms which has same atomic number but different neutron, and different mass number are known as the isotopes,

And an  average isotope mass of an isotopic mixture for an element called the relatively mass in a definite environment on the earth,

determines the element’s standard atomic weight.

Atoms which has same atomic mass number but has different atomic number are known as isobars of an element. Historically there are three isotopes of hydrogen is present in the nature

Types of Isotopes –

  1. Protium
  2. Deuterium
  3. Tritium

Basically only these three isotopes are found in nature in open state.

Atomic mass indicates the size of an atom. Although basically the mass is the sum of the mass of the protons, neutrons and electron in an atom.

The mass of an electron is so much less than than that of the other particles, that the mass is simply that of the nucleus.

Until the time of 1960’s chemists and physicists used different atomic mass scales. Chemist scientist used a scale that showed the natural mixture of oxygen isotopes had an atomic mass.

Standard atomic weight is the average of the relative atomic mass of an element in the crust of the earth and it’s atmosphere.

This is what is included in the standard periodic tables. Atomic weight is being fade out slowly and being replaced by relatively atomic mass.

Atomic weight is different from atomic mass in that it refers to the most abundant isotopes in an element and it is directly addressed a single atom or isotopes.

It and standard mass can be so close in elements with a single dominant isotopes, that there is a little difference present between when considering bulk calculation.  Large variations can occur in element with many common isotopes.

Both have their places in the modern science today.

In now’s day it is going out of fashion from when then atomic number is come

Because the most trusted periodic table modern periodic table is totally based on the atomic number.

Discovery of Atomic mass

Atomic weight is too much complicated as compared to atomic number like it is easy to remember the elements on the basis of atomic number as compared to atomic weight.

It is difficult to find atomic weight as compared to atomic number.

The first scientists who determine relative it were John Dalton and Thomas Thomson between 1803 and 1805 and Jons Jakob Berzelius between 1808 and in 1826.

Relative atomic mass or atomic mass was originally defined relative to that of the lightest element, hydrogen,

Which was taken as 1.00 and in the 1820s, Prout’s hypothesis started that atomic mass of all element would prove to be exact multiples of that of hydrogen.

I know these things are something complicated but it is not mandatory to know about all these theories, it is only for your common knowledge.

 Berzelius, however soon proved that this was not even approximately true,and for some elements such as chlorine,

Atomic weight

Relative it is about 35.5 falls almost exactly halfway  between two intergral multiples of that hydrogen.

The term of atomic weight is being phased out slowly with the time and being replaced by atomic number in most current usages.

Atomic mass is very complicated as compared to atomic number, That’s why it is being fade out as with time.

After coming of modern periodic table nobody think about atomic mass but it does not means that it can be removed from the chemistry science.

It has own place in the modern chemistry science, without atomic mass most of task is almost incomplete. Scientist still use it now in a large quantity.


Well I  think now you can understand all about the atomic mass and atomic number. I completed all the questions and queries in my all articles.

You should know more about the atomic mass and atomic number because it is a huge topic, it can not be explained by in a simple language. It goes deep and deep.


What is the average weight of an atom ?

The average weight of an single atom is depend on what type of element it is, like as weight of oxygen is 15.999 u.

What is the weight of carbon atom ?

The weight of an single carbon atom is 15.0107 u

Are all types of atoms or elements has atomic mass ?

Yes, All 118 types of atoms or elements has it’s different atomic masses.



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