Atomic Masses

Atom is the tiniest chemical element on earth that cannot be broken down any smaller. It is the basic unit of matter. The building block of every particle of matter in this world. No matter how great or small, every matter has a quantity of its own, called the mass. The total quantity of particles inside an atom is known as the atomic mass. Every atom has a specific property that determines its physical and chemical nature; atomic mass is one of those properties.

Isotope is atoms of the same element that have the same number of protons but with different nuclear masses and genuine properties. For example, carbon -12, carbon -13, and Carbon-14 are isotopes of carbon.

Isobar, in atomic physical science, atoms that have a similar mass number i.e., the same number of nucleons but different atomic numbers. Accordingly, chlorine-37 and argon-37 are isobars. Chlorine-37 has 17 protons and 20 neutrons in its core, though argon-37 has a core involving 18 protons and 19 neutrons. 

Isotone in at least two types of molecules or nuclei has similar neutrons. Hence, chlorine-37 and potassium-39 are isotones because the nucleus of this type of chlorine comprises 17 protons and 20 neutrons, while the core of this type of potassium contains 19 protons and 20 neutrons.

What is Atomic Mass?

An atom is made up of three basic particles- protons, neutrons, and electrons. Here, protons and neutrons are the larger particles, whereas electron is quite small in size. Therefore, atomic mass is the total number of protons and neutrons present in an Atom. Smaller in size, the electrons are not taken into consideration.

Atomic Mass Unit

An Atom, being very small in size and mass, is not easy or convenient to measure with a normal measuring unit. Previously, scientists used experiments to measure the mass of an atom about another. A unit of mass used to describe the mass of the atomic and subatomic particles is called the atomic mass unit. The atomic mass will vary depending on the number of protons and neutrons inside it, and it will be different for every other element.  

Atomic mass Unit or ‘u’ states the mass of an atom. One atomic mass unit is defined as a mass that is one-twelfth of a Carbon-12 atom. Carbon is taken as a standard element because there is no other element whose nucleus has a balanced number of protons and neutrons in it. 

How to Calculate Atomic Mass?

The combined masses of protons and neutrons account for nearly all the mass of an atom, the atomic mass of a single atom may be computed by adding the total number of protons and neutrons of that isotope.

An Isotope is an element that has the same number of protons and electrons but a different number of neutrons in its nucleus. 

A given atom’s atomic number is always equal to its number of protons. Because oxygen has an atomic number of 8, the total number of protons in an oxygen atom is also 8. When describing which isotope an atom belongs to, the total number of neutrons is given to us for computation.

Atomic Weight

There are numerous isotopes of a single element. Isotope masses must be considered when calculating the atomic weight. The percentage of isotopes may vary. The relatively abundant isotopes and the mass, both must be taken into consideration when computing atomic weight. Based on the abundance of isotopes, atomic weight is the average of the mass of all the atoms in an element. 

The atomic mass unit, which is 1/12th the mass of a carbon-12 atom, helps calculate atomic mass and atomic weight.

Mass Defect

Mass Defect is the difference between the mass of an atom and the sum of the masses of the protons, neutrons, and electrons present in it. While calculating the atomic mass of an element, we only consider the number of protons and neutrons in it. Therefore, this condition brings about a difference in the atomic mass and the isotopic mass of the element. It occurs because of two main reasons:

1. The neutron is slightly heavier than the proton, therefore, increasing the mass of the nucleus about the standard atomic mass unit scale based on the Carbon 12 element. 
2. An element whose nucleus has greater binding energy tends to have lower total energy and, therefore, a lower mass.

Difference Between Atomic Mass and Atomic Weight

1. Atomic mass is the sum of the number of protons and neutrons present in an atom whereas, Atomic weight denotes the average of the mass of all the atoms of an element.
2. The presence of the isotopes is not considered while calculating atomic mass, but Atomic weight is calculated by taking into consideration all of the isotopes in an atom.
3. Atomic mass can provide a value in a whole number but, in the case of atomic weight, the calculated value is not a whole number.
4. The only condition for the atomic mass of an element to be equal to its atomic weight is that it should have only one isotope.

Atomic Mass of Carbon

Carbon has an atomic number of 6. It states that there are 6 protons and 6 electrons in its atomic structure. We also know that carbon is an element whose number of protons is equal to the number of neutrons, which would be 6. Hence, the atomic mass is the sum of its protons and neutrons, which will be 12; therefore, 12u is the atomic mass of Carbon.

Problem Sum to calculate Atomic Mass

Calculate the atomic mass of an element with an atomic number of 18 and a neutron number of 20.

Solution: The number of protons = 18.

                 The number of neutrons = 20.

Atomic mass is the mass of an atom= Number of protons + Number of neutrons

A= 18 + 20

Therefore, the atomic mass of this element is 38u.

Conclusion

No matter how great or small, every matter has a quantity of its own called the mass. The total quantity of particles inside an atom is the atomic mass. It is the total number of protons and neutrons present in an atom. Although, while calculating the atomic mass of an element, we only consider the number of protons and neutrons, not the electrons; hence, it causes a mass defect. Atomic mass unit, or ‘u’, states the mass of an atom. One atomic mass unit is defined as a mass that is one-twelfth of a Carbon-12 atom. Carbon is taken as a standard element because there is no other element with a nucleus composed of a balanced number of protons and neutrons; whereas, atomic weight is the average mass of all the atoms in an element.