The Atom Calculator determines the number of protons, neutrons, and electrons in any atom or ion from atomic number, mass number, and charge. The foundational reference for chemistry students learning atomic structure, isotopes, electron configuration, and periodic table relationships.
6
6
6
12.0957
6
6
6
12.0957
Every chemical property of an element traces back to its atomic structure — the number of protons that defines the element, the neutrons that determine the isotope, and the electrons that govern all chemistry. The calculator for atom composition finds the number of protons, neutrons, and electrons for any atom or ion from just three inputs: atomic number, mass number, and ionic charge.
The fundamental counting rules for atomic composition:
Use this online calculator for any element and any isotope or ion. The atomic mass calculator computes the weighted average atomic mass from isotope abundances.
Isotopes are atoms of the same element (same atomic number, same proton count) with different numbers of neutrons — and therefore different mass numbers. All isotopes of an element have nearly identical chemical properties (same electron configuration) but different nuclear properties (stability, nuclear reactions):
The element's standard atomic weight on the periodic table is the weighted average across all stable isotopes, which is why it is rarely a whole number.
Ions form when atoms gain or lose electrons. The periodic table position predicts typical ionic charges:
Transition metals can form multiple ionic charges (Fe²⁺ and Fe³⁺; Cu⁺ and Cu²⁺), which is why their compounds have variable names (iron(II) vs. iron(III)). The average atomic mass calculator and atomic and molecular calculators provide complementary tools for atomic structure and composition calculations.
The number of electrons determines the electron configuration — the arrangement of electrons in shells and subshells that governs chemical bonding, reactivity, and spectroscopic properties. The aufbau principle fills subshells in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, ... For Fe (Z=26): [Ar] 3d⁶ 4s² in the neutral atom; Fe²⁺ ([Ar] 3d⁶) has lost both 4s electrons; Fe³⁺ ([Ar] 3d⁵) additionally loses one 3d electron to achieve a half-filled d subshell stability. Knowing the electron count from atomic number and ionic charge is the starting point for all electron configuration and periodic trend analysis.
The calculator applies these fundamental relationships from atomic physics:
The mass defect is the difference between the sum of individual nucleon masses and the actual measured atomic mass. This missing mass has been converted to the nuclear binding energy that holds the nucleus together. For example, helium-4 has a mass defect of about 0.0304 amu, corresponding to 28.3 MeV of binding energy. Understanding these relationships is essential in nuclear chemistry and physics.
The results show the complete subatomic particle inventory of your specified atom or ion. A higher neutron-to-proton ratio is typical of heavier elements and is necessary for nuclear stability. If the electron count differs from the proton count, the species is an ion. The approximate nuclear mass will always be slightly higher than the experimentally measured atomic mass, with the difference representing the binding energy that stabilizes the nucleus. Elements with the highest binding energy per nucleon (around iron-56) are the most stable.
Inputs
Results
Carbon-12 is the standard reference isotope for atomic mass measurements. It has equal numbers of protons, neutrons, and electrons (6 each). The approximate nuclear mass of 12.096 amu exceeds the defined mass of exactly 12.000 amu, with the 0.096 amu difference representing the nuclear binding energy.
Inputs
Results
Iron-56 is the most tightly bound nucleus per nucleon. As a Fe2+ cation, it has lost 2 electrons (24 remaining). The 30 neutrons give a neutron-to-proton ratio of 1.15, typical for mid-weight elements. Iron-56 has the highest binding energy per nucleon of any isotope.
The atomic number (Z) is the number of protons in the nucleus and uniquely identifies an element. The mass number (A) is the total number of protons plus neutrons (nucleons). Different isotopes of the same element have the same atomic number but different mass numbers because they have different numbers of neutrons.
Ions are atoms that have gained or lost electrons. A cation (positive ion) has fewer electrons than protons, formed when an atom loses electrons. An anion (negative ion) has more electrons than protons, formed when an atom gains electrons. The nucleus (protons and neutrons) remains unchanged during ion formation.
The sum of individual nucleon masses is always greater than the measured atomic mass. This difference, called the mass defect, represents the nuclear binding energy according to Einstein's equation E = mc². The binding energy is the energy required to disassemble the nucleus into separate protons and neutrons.
Nuclear stability depends on the neutron-to-proton ratio and the total number of nucleons. Light stable nuclei have roughly equal numbers of protons and neutrons (N/Z near 1). Heavier stable nuclei require more neutrons (N/Z up to about 1.5). Nuclei with magic numbers of protons or neutrons (2, 8, 20, 28, 50, 82, 126) are especially stable.
Yes. Protium (hydrogen-1) is the only stable nuclide with zero neutrons. Its nucleus consists of a single proton. All other stable atoms require at least one neutron. Helium-2 (diproton) with zero neutrons is extremely unstable and decays almost instantly.
Isotopes are atoms of the same element (same Z) with different numbers of neutrons (different A). They are written as Element-A, such as Carbon-12 and Carbon-14. Both have 6 protons, but Carbon-12 has 6 neutrons while Carbon-14 has 8. Isotopes have nearly identical chemical properties but different nuclear properties and masses.
How helpful was this calculator?
Be the first to rate!
