Atomic Notation Calculator

Build atomic notation and find the protons, neutrons, and electrons for an atom or ion.

Atomic notation

¹²₆C

Carbon-12 atom

Neutral atom

Protons: 6
Neutrons: 6
Electrons: 6
Atomic number: 6
Mass number: 12
Charge: 0

Try an example:

How it was calculated

Protons

Neutrons

12 − 6 = 6

Electrons

6 − 0 = 6

What is atomic notation?

Atomic notation shows an element's mass number and atomic number next to its symbol. A charge can be added to show whether the atom is an ion.

ᴬZXᑫ

A —: mass number
Z —: atomic number
X —: element symbol
q —: ionic charge

The three numbers to remember

Protons = atomic number

p = Z

Neutrons = mass number − atomic number

n = A − Z

Electrons = protons − charge

e = Z − q

A negative charge increases the number of electrons.

Cl⁻ → 17 − (−1) = 18 electrons

Important note

Mass number is not the same as atomic mass. Mass number is the whole-number total of protons and neutrons for one isotope. Atomic mass on a periodic table is usually a decimal weighted average of naturally occurring isotopes.

Common mistakes

Confusing atomic number with mass number

Using decimal atomic mass instead of the isotope's mass number

Forgetting that a positive ion has fewer electrons

Forgetting that a negative ion has more electrons

Using the charge incorrectly when calculating electrons

Mixing up isotope notation and ion notation

Related tools

Need to count atoms in a chemical formula?

Atom Counter

Need the molar mass of a compound?

Molar Mass Calculator

Need the percentage of each element in a compound?

Percent Composition Calculator

FAQ

Frequently asked questions

What is atomic notation?

Atomic notation shows an element symbol together with its mass number and atomic number, with the ionic charge shown when needed.

How do I find the number of neutrons?

Subtract the atomic number from the mass number: neutrons = mass number − atomic number.

How do I find the number of electrons in an ion?

Start with the number of protons and subtract the charge: electrons = protons − charge. A positive ion has fewer electrons, while a negative ion has more.

What is the difference between atomic number and mass number?

Atomic number is the number of protons. Mass number is the total number of protons and neutrons.

What does the top number in atomic notation mean?

The top number is the mass number, which equals protons + neutrons.

What does the bottom number mean?

The bottom number is the atomic number, which equals the number of protons.

Can an atom be both an isotope and an ion?

Yes. An isotope identifies the number of protons and neutrons, while an ion identifies the electron charge. An atom can have both an isotope and a charge.