How Is the Mass of a Proton Measured in Chemistry?
Proton is an elementary subatomic particle which is identical with the nucleus of the hydrogen atom and is made up of current quarks. It is denoted by p or p+. The location of Proton is inside the nucleus only and the charge of proton is positive that is +1e elementary charge. The Proton mass is slightly less than the neutron mass and mass of proton can be measured using the units kg,MeV/c, and u (amu). Proton along with the neutron is a constituent of all other atomic nuclei, that carries a positive charge.Both Protons and neutrons, each with masses of one atomic unit approximately they are together referred to as nucleons (particles present in atomic nuclei).
Mass of Proton
The mass of the proton is the sum of the total mass of current quarks and the binding gluons. Protons and neutrons are made up of smaller particles and are classified as baryons—particles composed of three elementary units of matter known as quarks and the strong interaction between these sub-particles is mediated by the exchange of massless particles called gluons that act between quarks.
The Mass of the Proton is
Proton Mass mp = 1.672621898(21)×10−27 Kg
Mass of Proton in Other Units
The mass of the proton can be denoted in a number of units like – proton mass amu, mass of proton in kg, proton mass MeV.
The proton mass in different units are as follows:
Mass of proton in kg is 1.672621898(21)×10−27 kg
Mass of proton in grams is 1.672621898(21)×10−24 g
Mass of proton in amu is 1.007276466879(91) u
Mass of proton or proton mass in MeV is 938.2720813(58) MeV/c2
Proton Mass Calculation
Goldstein in the year 1886 in his experiment noticed that the charge to mass ratio of the positive particles depends on the nature of the gas which is present in the discharge tube which means that the charge to mass ratio (e/m) is different for the different gases. He observed that the charge to mass ratio of the positive rays was more in case of the hydrogen gas, was used in the discharge tube which was mainly because hydrogen is the lightest atom so m will be the least thus the e/m ratio will be more or highest in this case. These particles in the positive rays in the discharge tube were later named as a proton. We can also say that a proton can be produced by removing an electron from the hydrogen atom. Thus, it can also be said that proton is a hydrogen ion (H+).
There Are Three Methods That Use Different Approaches to Find the Atomic Mass of a Proton. These Three Methods Are:
Calculation from theory
Atomic Mass Method
Charge/Mass comparisons with electron
1. Calculation from Theory: Albert Einstein came up with his revolutionary theory, “the theory of relativity” during the 20th century. The theory brilliantly explained that mass and energy are interchangeable; the mass can be converted into energy and vise-versa. In this method, we derive the mass of protons from the above-mentioned theory.
Protons have an internal structure- three forces (quarks) that hold together with attraction forces (gluons). Now according to the naive norms, they would give each quark about 1/3 mass of a proton. But, in reality, quark mass does not contribute 95 to 98% of the mass of a proton.
In reality, most of the mass of a proton is derived from interaction energy between the quarks using the mass and energy are interchangeable theory i.e. E =mc2.
2. By Atomic Molar Mass Method: In the hydrogen atom one mole or 6.02214076×1023 particles weighs 1.0079 g thus each mole of proton in one hydrogen atom weighs 1.0079g.
Since one mole equals 6.02214076×1023 particles, and we know that protons weigh 1.0079 g. Then dividing the weight of the proton with the mole number we get (1.0079 /6.022×1023) Thus the proton mass equals 1.6737×10-24 g.
Note: in the atom, there is an electron to balance the proton charge. Also, we can do this experiment with any element of the periodic table.
3. Charge/Mass Comparisons with Electron: In this method, the atom’s bend is measured when it enters the standardized electric and magnetic fields. In addition, the bending magnitude also indicates the proton mass by comparing it with electron mass. The main idea of an experiment is similar to inducing the motion of a rolling ball where a constant force (mechanical force) will always deflect a heavy proton from a straight-line movement to a small extent. This deflection in electrons is even more.
FAQs on Proton Mass: Definition, Value, and Units
1. What is the definition of proton mass and what is its value in kilograms?
Proton mass is the rest mass of a proton, a subatomic particle with a positive electric charge. It is a fundamental physical constant. The accepted value for the mass of a proton is approximately 1.6726219 × 10⁻²⁷ kilograms (kg). This value is crucial for calculations in atomic and nuclear physics.
2. How is the mass of a proton expressed in other common units?
The mass of a proton can be expressed in various units depending on the context of the scientific field. The most common units are:
- Atomic Mass Units (amu): 1.007276 amu. This unit is standard in chemistry for comparing the masses of atoms and subatomic particles.
- Grams (g): 1.6726219 × 10⁻²⁴ g.
- Mega-electronvolts (MeV/c²): Approximately 938.272 MeV/c². This unit, derived from Einstein's mass-energy equivalence principle (E=mc²), is commonly used in nuclear and particle physics.
3. How does the mass of a proton compare to the mass of a neutron and an electron?
A proton is significantly heavier than an electron but has a mass very similar to that of a neutron.
- A proton is approximately 1836 times more massive than an electron. Due to this large difference, the mass of electrons is often considered negligible when calculating an atom's mass number.
- The mass of a proton (1.007276 amu) is slightly less than the mass of a neutron (1.008665 amu).
4. What is the relationship between the mass of a proton and the mass of a hydrogen atom?
The mass of a standard hydrogen atom (protium, ¹H) is almost equal to the mass of a single proton. This is because a hydrogen atom consists of one proton and one electron. Since the electron's mass is negligible compared to the proton's, the atomic mass of hydrogen is primarily determined by the mass of its proton.
5. Why is the mass of a proton not exactly equal to 1 atomic mass unit (amu)?
This is a common point of confusion. The atomic mass unit (amu) is defined as one-twelfth (1/12th) of the mass of a single, unbonded carbon-12 atom in its ground state. A carbon-12 atom contains 6 protons, 6 neutrons, and 6 electrons. The mass of a single proton (1.007276 amu) is slightly more than 1 amu because the binding energy that holds the nucleus together affects the total mass. Therefore, while close to 1, a proton's mass is not the exact standard for the amu.
6. What are protons made of, and how do these components create its mass?
Protons are not fundamental particles; they have an internal structure. A proton is composed of smaller elementary particles called quarks and gluons. Specifically, it consists of:
- Two 'up' quarks and one 'down' quark.
- Gluons, which are the force-carrying particles that "glue" the quarks together.
Interestingly, the rest masses of the quarks only account for about 1% of the proton's total mass. The remaining 99% comes from the immense kinetic energy of the quarks and the binding energy of the gluons, as described by Einstein's equation E=mc².
7. Why is understanding proton mass important for defining a chemical element?
The mass of protons is fundamental to chemistry and the periodic table. Protons, along with neutrons, reside in the nucleus and make up nearly all of an atom's mass. This total mass is known as the mass number (A). While the number of protons (the atomic number, Z) defines the element's identity (e.g., any atom with 6 protons is carbon), the proton mass is a key contributor to the atom's overall mass, which influences its physical properties like density and its behaviour in nuclear reactions.
