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Atomic Mass of Phosphorus

There are four phosphorus atoms in each phosphorus molecule. Phosphorus has an atomic mass of 30.97 amu (atomic mass unit). Phosphorus has a molar mass of 123.88 g/mol and is a chemical element.

Phosphorus is a chemical element with the symbol P and the atomic number 15. It is found in nature in small amounts. Elemental phosphorus comes in two major forms: white phosphorus and red phosphorus. However, due to the extreme reactivity of phosphorus, it is never found as a free element on the surface of the Earth. This element has a concentration of around one gramme per kilogramme of the Earth’s crust (compare copper at about 0.06 grams). Phosphorus is most commonly found in the form of phosphate in minerals.

Atomic Mass of Phosphorus

Phosphorus has an atomic mass of 30.973762 u.

Atomic mass is defined as the number of protons and neutrons in an atom where the mass of each proton and neutron is about 1 amu. The mass of each proton and neutron is approximately 1 amu (1.0073 and 1.0087, respectively). The electrons in an atom have such a small mass when compared to the protons and neutrons that their mass is virtually non-existent. The carbon-12 molecule, which is still in use as a standard today, is composed of six protons and six neutrons, with an atomic mass of twelve amu. It has a total of twelve protons and six neutrons.

The weight of an atom, in contrast to the weight of an item, has nothing to do with the force of gravitation. In this case, it is a unit-less figure that represents the relationship between atomic masses of naturally occurring isotopes of an element and the atomic mass of one-twelfth of the mass of carbon-12. When it comes to elements with only one naturally occurring isotope, such as beryllium or fluorine, the atomic mass is equal to the atomic weight of the element. 

It is the weighted average of the atomic masses of the element’s isotopes on a scale where the carbon-12 atom has an exact mass of 12 units that is used to calculate its relative atomic mass.

Isotopes of phosphorus

Despite the fact that phosphorus (15P) has 23 stable isotopes ranging from 25P to 47P, only 31P is stable, and as a result, phosphorus is classified as a monoisotopic element.

The radioactive isotopes with the longest half-lives are 33P, which has a half-life of 25.34 days, and 32P, which has a half-life of 14.268 days.  All others have half-lives of less than 2.5 minutes, with the majority of them being less than a second. The least stable is 25P, which has a half-life of fewer than 30 nanoseconds and is the least stable.

Phosphorus 32 (P-32)

With a mass number spanning from 24 to 46, phosphorus (P) has 23 known isotopes, each with a different mass number. Phosphorus is a monoisotopic element since there is only one stable isotope, P-31.

Phosphorus 33 (P-33) has a half-life of 25.34 days, while phosphorus 32 (P-32) has a half-life of 25.34 days. Phosphorus 33 (P-33) and phosphorus 32 (P-32) are the radioisotopes of phosphorus with the longest half-lives (14.263 days). All other isotopes have a half-life of fewer than 2.5 minutes, and the vast majority of them have a half-life of less than one second, as well.

When it comes to phosphorus isotopes, phosphorus 32 (P-32) is the one whose nucleus has 15 protons and 17 neutrons. β- (1.71 MeV)  particle in 32S with a half-life of 14.263 days is emitted as a byproduct of its disintegration. It is a radioactive material created by bombarding stable phosphorus with neutrons in a controlled environment.

Phosphorus 32 is a high-energy beta-pure emitter with a continuous spectrum that has a maximum energy of 1.7 MeV and average energy of 0.7 MeV. The continuous spectrum of phosphorus 32 has a maximum energy of 1.7 MeV and average energy of 0.7 MeV.

Phosphorus 32 is one of the most often utilised research emitters, and it also happens to be the one with the most energy. Its application in molecular biology has grown in popularity as a result of the widespread usage of certain high-activity nucleotides to label DNA.

Phosphorus 32 can also be employed in phosphorylation processes, although this is less common. The technique is specifically employed in the investigation of the migration of fertilisers (phosphates) in soils.

When it comes to the medical field, phosphorus-32 has been used to treat polyglossia, but this is becoming less common.


Its half-life is 25.4 days, and it is a beta-emitter (0.25 MeV) with a beta-emission of 33P. It is utilised in life-science laboratories for applications where lower energy beta emissions are favourable, such as DNA sequencing, where lower beta emissions are advantageous. Nucleotides can be labeled with the radioactive element 33P. It has a lower energy requirement than 32P and so provides higher resolution. One downside of 31P is that it is more expensive than 32P since most of the blasted 31P will have received only one neutron, whereas only a few will have received two or more neutrons. It has a specific activity of 5118 Ci/mol at its highest concentration.


Phosphorus is an essential mineral that is required by every cell in the body in order for it to operate properly. Phosphorus is found in the body as the compound phosphate (PO43-), which is bound to oxygen in all biological systems. Approximately 85 percent of the phosphorus in the body is contained in the bones and teeth, according to the National Institute of Health.

When expressed in atomic mass units, the phosphorus atom has an atomic mass of 30.974 and represents the average mass of all naturally occurring phosphorus atoms on Earth (or daltons, D). A phosphorus atom contains 30.974-15 = 16 neutrons, which allows for the determination of the number of neutrons contained within the nucleus.


Frequently asked questions

Get answers to the most common queries related to the NEET UG Examination Preparation.

Who discovered phosphorus 33?

Ans. merchant Hennig Brand.

What is the purpose of phosphorus being held in water?

Ans. Because white phosphorus is insoluble in water, it must be stored underwater to avoid oxidation and degradation...Read full

What is the process through which P4 is formed?

Ans. Neither of the N atoms’ octets has been completed. P has a high atomic size and has a low proclivity for ...Read full

Which element of phosphorus is the most stable?

Ans. The most kinetically stable element is red phosphorus.

Which of the phosphorus allotropes is the most reactive?

Ans. White phosphorus Because of its pyramidal form and the strain invo...Read full