Free chemistry calculators for atomic properties, molarity, solutions, and conversions. Periodic table data included.
1 calculator
Advertisementslot: cat-top
Chemistry calculators turn the periodic table into an interactive reference. Look up any of the 118 known elements to see protons, neutrons, electrons, isotopes, and electron configuration; compute the mass of a specific isotope; or work out an ion's charge and electron count. The tools here use the IUPAC 2021 standard atomic weights — the same values used in peer-reviewed chemistry — rather than older rounded numbers.
Each calculator includes the chemical context for what you're computing: not just the answer, but why that's the answer and how it connects to the element's position on the periodic table. Useful for chemistry students learning the periodic table, lab work that needs quick lookup, or anyone curious about the building blocks of matter.
Atomic mass is the mass of one atom of an element, expressed in atomic mass units (u or amu). One u is defined as exactly 1/12 the mass of a carbon-12 atom, which is approximately 1.66053906892 × 10⁻²⁷ kg. The "atomic weight" you see on the periodic table is actually a weighted average across all naturally-occurring isotopes of an element, which is why it's usually not a whole number.
What's the difference between an isotope and an ion?
Isotopes differ in their number of neutrons — same element, same chemical behavior, different mass. Carbon-12 and carbon-14 are both carbon, but C-14 has two extra neutrons. Ions differ in their number of electrons — same nucleus, different charge, often different chemical behavior. Na⁺ is a sodium atom that lost an electron; Cl⁻ is a chlorine atom that gained one. An atom can be both an isotope and an ion simultaneously.
Why don't atomic masses appear as whole numbers?
Two reasons. First, the standard atomic weight is a weighted average over all naturally-occurring isotopes — chlorine appears as ~35.45 because Earth's chlorine is roughly 76% Cl-35 and 24% Cl-37. Second, even individual isotope masses aren't exactly whole numbers: nuclear binding energy converts a tiny bit of mass into binding energy (the "mass defect"). C-12 is defined as exactly 12 u, but other isotopes deviate slightly.
How do electrons arrange themselves in an atom?
Electrons fill orbitals starting with the lowest-energy shell (closest to the nucleus) and working outward, following the Aufbau principle, Pauli exclusion (no two electrons share all four quantum numbers), and Hund's rule (parallel spins first when filling orbitals of equal energy). The standard order is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on — there are some exceptions in the transition metals where d-orbital arrangements stabilize differently than the simple ordering predicts.