Atomic Mass Formula: Definition, Unit, Facts, Formula
Atomic Mass Formula is a fundamental concept in chemistry and physics. It represents the average mass of atoms in a given chemical element.
Yashasvi Tyagi13 Sept, 2023
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Atomic mass , often referred to as atomic weight, is a fundamental concept in chemistry and physics. It represents the average mass of atoms in a given chemical element, considering the relative abundance of its isotopes. Atoms, the building blocks of matter, consist of a nucleus containing protons and neutrons, surrounded by a cloud of electrons. The atomic mass is primarily determined by the combined mass of protons and neutrons in the nucleus, as electrons contribute only a negligible amount to the overall mass of an atom.
Atomic Mass
We know that every atom consists of three primary elements: protons, electrons, and neutrons.- Protons are positively charged subatomic particles present in the nucleus of the atom. Its mass is 1.6727 × 1 0 -24 g. It can also be represented in Atomic mass unit as 1.007316 amu.
- Electrons are negatively charged subatomic particles revolving around the nucleus in fixed orbits. Its mass is 9.11 × 1 0 -27 g . It can also be represented in Atomic mass unit as 0.000549 amu.
- Neutrons do not have a charge and are, therefore, neutral. They are also found in the nucleus of the atom. Its mass is 1.6750 × 1 0 -24 g. It can also be represented in Atomic mass unit as 1.008701 amu .
Also Check - Discovery of Proton Formula
On comparing the mass of electrons with protons and neutrons, one can easily understand that the mass of electrons is significantly less than that of protons and neutrons.The Formula for Atomic Mass
We read in the introduction that atomic mass is the sum of the mass of protons, neutrons, and electrons. Hence, the formula for atomic mass can be written as Atomic mass of an element = mass of protons( M P ) + mass of electrons( M E ) + Mass of neutrons( M N ). If we neglect the mass of electrons, the formula can be modified as Atomic mass of an element = mass of protons( M P )+ Mass of neutrons( M N ). For example, if we consider the element carbon, with 6 neutrons, 6 protons, and 6 electrons, Then, the atomic mass of carbon can be derived asDownload PDF Atomic Mass Formula
Also Check - Bond Order Formula
Atomic mass(A) = No of protons* Mass of Proton +No of neutrons* Mass of Neutrons +No of electrons* Mass of Electrons = 6*1.007316+6*1.008701+6*0.000549 = 12.099396 amu The atomic mass of elements| Element | Atomic mass(Amu) |
| Hydrogen | 1.008 |
| Helium | 4.002 |
| Lithium | 6.94 |
| Beryllium | 9.012 |
| Boron | 10.81 |
| Carbon | 12.011 |
| Nitrogen | 14.007 |
| Oxygen | 15.999 |
| Fluorine | 18.998 |
Methods to Calculate Atomic Mass
Using the Periodic Table
An atomic number is often given next to an element's representation in the periodic table. For instance,- Chlorine has an atomic mass of 35.5 and an atomic number of 17.
- The atomic mass of calcium is 40, with an atomic number of 20.
Adding the Mass of Protons and Neutrons
Since, protons and neutrons are present inside the atom's nucleus, their combined mass can be added to calculate the atomic mass.Isotope Method
The average atomic mass of different elements is calculated by dividing the average atomic mass of each isotope by the fractional abundance of that isotope, then adding the result. Chlorine, for instance, has two different sorts of atoms with relative masses of 35u and 37u. These isotopes are found in nature in a 3:1 ratio of relative abundance. The average of these several relative masses is hence the atomic mass of chlorine. The average Atomic Mass of Chlorine is thus calculated as follows: ((35 × 3)+(37 × 1))/4=35.5amuRelative Atomic Mass Formula
The Relative Atomic Mass of an element is the ratio of its mass to the total number of atoms in it. The relative Atomic Mass scale is used to calculate the masses of various atoms. The lightest atom, hydrogen, was given a Relative Atomic Mass of 1, and the relative atomic masses of other atoms were calculated in relation to this. The relative atomic mass of some elements| Hydrogen | 1 |
| Helium | 4 |
| Lithium | 7 |
| Beryllium | 9 |
| Boron | 11 |
| Carbon | 12 |
| Nitrogen | 14 |
| Oxygen | 16 |
| Fluorine | 18 |
Atomic Mass Formula FAQs
What is the atomic mass of an element?
An element is made up of several atoms which further contain several subatomic particles. These particles include protons, neutrons and electrons which have some mass. When the mass of all the protons, neutrons and electrons is added together, we get the atomic mass of the element.
What is the significance of atomic mass?
Atomic mass is crucial for understanding and predicting chemical reactions. It enables scientists to calculate the amounts of substances involved in reactions, determine reaction yields, and design procedures for the synthesis of compounds.
How is the atomic mass of an element calculated?
The atomic mass of an element can be calculated by adding the number of protons and neutrons present in the element. For instance, in a calcium atom, there are 20 neutrons and 20 protons. If we add the sum of the protons and neutrons, it comes out as 40 which is equivalent to the actual atomic mass of calcium (40.12amu).
How is the atomic mass different from the atomic number?
Atomic mass refers to the total mass of an atom, which includes the mass of its protons, neutrons, and electrons. It is typically expressed in atomic mass units (amu) or unified atomic mass units (u). The atomic number represents the number of protons in the nucleus of an atom. It is a whole number that uniquely identifies each element on the periodic table.
What is the formula for calculating the atomic mass?
The atomic mass can be calculated using the weighted average method or by adding the number of neutrons and protons. To calculate the atomic weight of the element, you'll use the isotopic masses and their abundances.
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