Atom Calculator

Atoms are the basic units of chemical elements. Each atom has a compact nucleus containing positively charged protons and usually neutral neutrons, surrounded by negatively charged electrons. The atomic number Z is the proton count and uniquely identifies the element. A neutral atom has the same number of electrons as protons. The mass number A is the whole-number total of protons and neutrons for one isotope, so neutron count is A minus Z. Isotopes belong to the same element because they have the same proton count, but they contain different numbers of neutrons. Natural samples usually contain a mixture of isotopes. The atomic mass printed on a periodic table is therefore a weighted average, not normally the mass number of one atom. To calculate that average, multiply each isotope mass by its relative abundance, add the products, and divide by the total abundance. The calculator accepts comma-separated masses and matching abundances. Since it divides by the abundance total, percentage lists and consistently scaled fractional lists produce the same weighted mean. The tool also connects microscopic particles with laboratory-scale quantities. One mole contains exactly 6.02214076 times 10 to the power of 23 specified entities, known as the Avogadro constant. Multiplying moles by that constant gives the number of atoms, molecules, ions, or formula units. Multiplying moles by molar mass gives grams, while dividing grams by molar mass gives moles. The selected entity must remain clear: one mole of oxygen atoms and one mole of oxygen molecules contain the same count of entities but have different molar masses. For common symbols in this compact reference set, the calculator can supply a standard molar mass and atomic number. Explicit isotope data takes priority for the weighted mass, and an entered mass number can act as a simple molar-mass approximation when no reference value is available. Atomic number and mass number should be nonnegative integers, and mass number cannot be smaller than atomic number. Isotope abundances should describe the same sample and must correspond one-for-one with isotope masses. These calculations support chemistry homework, stoichiometric planning, isotope interpretation, and quick laboratory checks. They do not model ions because electron count is reported for a neutral atom, nor do they replace a complete periodic-table database or high-precision isotope standards. For analytical work, use the isotope masses and abundances appropriate to the sample and preserve enough significant figures to match the measurement quality.