Atom Calculator

Find the subatomic particle counts for any element. Select an element from the periodic table to get protons, neutrons, and electrons. Optionally specify a mass number for a specific isotope. This calculator uses the full periodic table.

Element*

Mass Number (A)

Mass number (protons + neutrons)

Number of Atoms

Calculate for multiple atoms

ATOM STRUCTURE: 1. PROTONS (p+): = Atomic number (Z) = Identifies the element = Equals electrons in neutral atom 2. NEUTRONS (n⁰): = Mass number (A) - Atomic number (Z) = May vary (isotopes) = No charge 3. ELECTRONS (e⁻): = Protons in neutral atom = Determines chemical behavior = Can vary in ions NOTATION: ^A_Z Symbol - A = mass number (protons + neutrons) - Z = atomic number (protons) - Symbol = element symbol MASS NUMBER: A = p+ + n⁰

Example: Calculate for Carbon-12 (¹²₆C) 1. Look up Carbon: Z = 6 2. Given mass number: A = 12 3. Protons = Z = 6 4. Neutrons = A - Z = 12 - 6 = 6 5. Electrons = 6 (neutral) 6. Notation confirms: ¹²₆C has 6p, 6n, 6e For multiple atoms: 5 carbon atoms = 5 × 6p = 30p, 30n, 30e Total mass = 5 × 12 = 60 u

How do I find the number of protons, neutrons, and electrons in an atom?

Protons = atomic number (Z) from the periodic table—1 for H, 6 for C, 79 for Au. Neutrons = mass number (A) minus atomic number. Electrons = protons in a neutral atom. For ions, electrons adjust: negative ions have extra electrons, positive ions have fewer. Mass number is protons plus neutrons—Carbon-12 has 6p+6n=12, Carbon-14 has 6p+8n=14.

What's the difference between atomic number and mass number?

Atomic number (Z) is protons—the element's identity. Change Z = different element. Mass number (A) is total nucleons (protons + neutrons)—determines isotope. Carbon (Z=6) can have A=12, 13, or 14 (different neutron counts). Both are shown in isotope notation: ¹²₆C.

What are isotopes?

Isotopes are same element (same protons) but different neutron counts. Carbon-12 (6n) is stable, 95% natural. Carbon-14 (8n) is radioactive, used in dating. Tritium (³H) has 2 neutrons, regular hydrogen (¹H) has zero. Isotopes have same chemical behavior, different nuclear properties.

How do electrons relate to the atom?

Neutral atoms have equal protons and electrons. Electrons determine chemical bonding and reactivity. They occupy energy levels/shells: 2 in first, 8 in second, 18 in third, 32 in fourth (2n²). Electron configuration explains periodic trends and bonding patterns.

What is atomic mass?

Atomic mass is the average mass of all natural isotopes, weighted by abundance. Carbon: 12.01 u (mostly C-12 with some C-13). The atomic mass in the periodic table is this weighted average—not the mass of any single atom.

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