proton relative mass

proton relative mass

proton relative mass
proton relative mass

The atomic model consists of a nucleus containing protons and neutrons, surrounded by electrons in shells. The numbers of particles in an atom can be calculated from its atomic number and mass number.

The current model of an atom has a positively charged central nucleus surrounded by negatively charged electrons arranged in shells.

The nucleus is very small compared to the atom as a whole:

The nuclei of all atoms contain subatomic particles called protons and most also contain neutrons.

proton relative mass

The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, their relative masses are used. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.

The mass of electrons is very small compared to protons and neutrons. Since a nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.

Protons and electrons have opposite electrical charges.

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Atoms contain protons, neutrons and electrons. The electrons are arranged in shells around the nucleus. The periodic table is a chart of all the elements arranged in increasing atomic number.

Atoms contain three sub-atomic particles called protons, neutrons and electrons.

The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in shells around the nucleus.

The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overall.

proton relative mass

Atoms can lose or gain electrons. When they do, they form charged particles called ions:

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proton relative mass

(Why do protons and neutronshave the same mass?)

What are the exact relative masses of protons, neutrons and electrons?

Protons and neutrons have nearly the same mass while electrons are much less massive. If we assume that a neutron has a mass of 1, then the relative masses are:

Neutron = 1Proton = 0.99862349Electron = 0.00054386734

Said another way, protons are only about 99.86% as massive as neutrons while electrons are only about 0.054% as massive as neutrons. While relative masses are nice if you want to compare protons, neutrons and electrons to one another, it doesn’t tell you what the actual masses of these particles are. In kilograms, the masses are:

  • 2800 divided by 4
  • Neutron = 1.6749286*10-27 kgProton = 1.6726231*10-27 kgElectron = 9.1093897*10-31 kg

    There is another unit, called an electron volt (eV), that scientists use when talking about small things like protons, neutrons and electrons. An electron volt is actually a measurement of energy, but scientists can get away with using it to measure mass since mass and energy are related by Einstein’s famous equation, E = mc2. So, in terms of MeV (Megaelectron volts, 1 MeV = 1,000,000 eV), the masses are:

    Neutron = 939.56563 MeVProton = 938.27231 MeVElectron = 0.51099906 MeV


    Steve Gagnon, Science Education Specialist (Other answers by Steve Gagnon)

    Related Pages:

    If different types of quarks have different masses, then why are protons and neutrons said to have the same mass, when they have different compositions of quarks?

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    The relative mass of a proton is 1. The relative mass of a neutron is 1. The relative mass of an electron is 1/1840 (accept 0).


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    IB Chemistry home > Syllabus
    2016 > Atomic theory > Relative mass and

    ref: 2.1

    Atoms differ from one another suggesting that the arrangement of sub-atomic
    particles is different from atom to atom. One way that they differ is
    in terms of mass.

    Particle mass

    The actual masses of these sub-atomic particles are very small and to the
    nearest whole number measured relative to the mass of a carbon-12 isotope
    being equal to 12 units:

    proton relative mass

    Although these values suggest that the protons and neutrons are identical
    they do, in fact, have very slightly different masses, which is only of concern
    to us when considering changes in the structure in nuclear chemistry. Compared
    to the mass of the protons and neutrons the electrons have negligible mass
    and can be ignored when carrying out calculations involving mass.

    Protons have a mass of 1 atomic mass unit. They are all together in the nucleus,
    but they cannot repel one another because of the strong nuclear force exerted
    by the protons and the neutrons. You could consider the neutrons to be the
    nuclear glue that holds the nucleus together.

    A full description of the electron is rather complicated as they behave
    both as particles in some circumstances and waves in others. This has
    lead quantum physicists to calling them wavicles – things that possess
    the characteristics of both particles and waves.

    This model allows us to use the atomic theory successfully to explain many
    observations in the microscopic world. Its use in modern particular science
    has been refined by the introduction of another model, which is rather more
    difficult to understand, called the quantum model.


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  • Electrical charges

    The forces that hold atoms together (and to one another) are largely electrical
    in nature (apart from the strong nuclear charge that binds the particles in
    the nucleus together).

    Electrically charged particles have an associated electrostatic field, rather
    like a magnet has a magnetic field. If another electrical charge comes into
    this field it will feel a force of either attraction or repulsion, depending
    on whether the charge carried is opposite or the same.

    Overall, atoms are neutral, which means that they must have as many positive
    charges as negative charges.

    Protons carry a single positive charge and the electrons carry a single negative
    charge, so in the neutral atom there are always the same number of protons
    and electrons.

    The electrons are tiny in comparison to the protons and neutrons. The overall
    charge on an atom is zero, the charges of the electrons cancel out the positive
    charges of the protons in the nucleus.

    Summary of fundamental particle charge and location


    proton relative mass
    proton relative mass
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