What are “particles” in this calculator?

Particles are formula units, molecules, or atoms of the substance. The calculator converts particles to moles using Avogadro’s number and multiplies by the atoms per formula unit to get total atoms.

No. The Atom Calculator converts between mass, moles, and particles; density is only needed if you want to convert from volume to mass.

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Atom Calculator

Q: When does isotopic composition apply?

When the formula is a single element or when you choose a specific element in the “count specific element” field. The tool will split expected atoms across isotopes using natural or custom abundances.

Q: Are isotopic outputs exact counts?

They are expected (average) counts based on percent abundance. Real samples contain integers; large samples closely match the expected distribution.

Convert between mass, moles, and particles and get the total number of atoms in a sample. Supports chemical formulas, auto molar mass, step-by-step solutions, and optional visual aids.

Background

For molar mass M (g·mol⁻¹), mass m (g), moles n (mol), particles N (formula units/molecules/atoms), and Avogadro’s number N_A=6.022×10²³: n = m / M; N = n·N_A. Total atoms = N × (atoms per formula unit).

Enter what you know (any one input is enough):

Chemical formula (element or compound):

We parse the formula to auto-compute molar mass M and atoms per formula unit.

Provide one of the following:

If you enter mass, M is required (we auto-fill from formula when possible). “Particles” means molecules/formula units/atoms of the substance.

Molar mass (M) override (optional):

If provided, this overrides the auto-computed M from the formula.

Optionally count atoms of a specific element:

Leave blank to get total atoms for the whole formula unit. Enter a symbol (e.g., C, H, O, Na).

Show:

Step-by-step working

Mini chart: N, n, m (with per-row scaling)

Round to sensible significant figures

Advanced (optional):

Isotopic composition

Illustration: atom count (dot cluster)

Quick picks:

Tip: Counting a specific element multiplies by its subscript in the formula.

Result:

No results yet. Enter inputs and click Calculate.

How to use this calculator

Formula: Enter an element or compound; we compute M and atoms per formula.
Given: Provide mass m, moles n, or particles N (one is enough).
Atoms: Total atoms = N × (atoms per formula); specific-atom count multiplies by that element’s subscript.
Advanced: Isotopic composition splits expected atoms across isotopes; dot cluster illustrates magnitude.

Formula & Equation Used

Relations: n = m / M; N = n · N_A, with N_A = 6.022 × 10²³ mol⁻¹.

Atoms per formula unit: sum of all subscripts in the formula (e.g., H₂O → 3; Ca(OH)₂ → Ca:1, O:2, H:2 → total 5).

Specific element atoms: atoms(X) = N × (subscript of X).

Isotopic split: atoms(isotope i) = atoms(X) × (abundance_i / 100).

Examples

2.30 g Na → atoms Na

M(Na)=22.99 g/mol; n = 2.30/22.99 = 0.100 mol; N = 0.100 × 6.022×10²³ = 6.02×10²² atoms.

0.250 mol Cl₂ → total atoms

N = 0.250 × 6.022×10²³ = 1.51×10²³ molecules; atoms per formula = 2 → total atoms = 3.01×10²³.

18.0 g H₂O → atoms of H

M≈18.015 g/mol; n ≈ 0.999 mol; N ≈ 6.02×10²³ molecules; H subscript = 2 → H atoms ≈ 1.20×10²⁴.

Frequently Asked Questions

Q: What are “particles” here?

They are formula units/molecules/atoms of the substance. We then multiply by subscripts to get total atoms.

Q: Do I need density?

No—unless you’re converting volumes to mass. This tool works from mass, moles, or particles.

Q: When does isotopic composition apply?

When the formula is a single element (e.g., Cl₂ → split into ³⁵Cl/³⁷Cl) or when you choose a specific element to count (e.g., “H” in H₂O).

Q: Are isotopic outputs exact counts?

They’re expected counts based on percent abundance (a statistical average), not literal integers in a particular sample.

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