Atom Calculator
Calculate the number of protons, neutrons, and electrons in any atom or ion. Find atomic mass, mass number, determine ion charges, explore isotopes, and look up any element from the periodic table with detailed atomic structure information.
How to Calculate Protons, Neutrons, and Electrons
Every atom consists of three subatomic particles: protons (positive), neutrons (neutral), and electrons (negative). Here's how to find each:
- Protons: Equals the atomic number (Z) — found on the periodic table
- Neutrons: Mass number (A) minus atomic number (Z): N = A - Z
- Electrons: For neutral atoms, equals protons. For ions: Electrons = Z - charge
Carbon-12 has 6 protons, 6 neutrons, and 6 electrons. It is a stable isotope and makes up 98.9% of naturally occurring carbon.
The calculated atomic mass is approximately 12.000 u. The actual mass may differ slightly due to binding energy (mass defect).
Sodium ion (Na⁺) has lost 1 electron, giving it 10 electrons while retaining 11 protons. This creates a +1 charge and makes it isoelectronic with neon.
📊 First 20 Elements Reference
| Z | Symbol | Name | Mass | Electrons |
|---|---|---|---|---|
| 1 | H | Hydrogen | 1.008 | 1 |
| 2 | He | Helium | 4.003 | 2 |
| 3 | Li | Lithium | 6.941 | 3 |
| 4 | Be | Beryllium | 9.012 | 4 |
| 5 | B | Boron | 10.81 | 5 |
| 6 | C | Carbon | 12.01 | 6 |
| 7 | N | Nitrogen | 14.01 | 7 |
| 8 | O | Oxygen | 16.00 | 8 |
| 9 | F | Fluorine | 19.00 | 9 |
| 10 | Ne | Neon | 20.18 | 10 |
| 11 | Na | Sodium | 22.99 | 11 |
| 12 | Mg | Magnesium | 24.31 | 12 |
| 13 | Al | Aluminum | 26.98 | 13 |
| 14 | Si | Silicon | 28.09 | 14 |
| 15 | P | Phosphorus | 30.97 | 15 |
| 16 | S | Sulfur | 32.07 | 16 |
| 17 | Cl | Chlorine | 35.45 | 17 |
| 18 | Ar | Argon | 39.95 | 18 |
| 19 | K | Potassium | 39.10 | 19 |
| 20 | Ca | Calcium | 40.08 | 20 |
Atomic masses shown are average atomic masses in atomic mass units (u). Source: IUPAC 2021.
📖 How to Use This Calculator
Choose Your Calculation Type
Select "Atomic Structure" to find protons/neutrons/electrons, "Atomic Mass" for mass calculations, "Ion Calculator" for charged atoms, or "Element Lookup" to explore the periodic table.
Enter Your Values
Input the atomic number (Z), mass number (A), and charge if applicable. Use the quick examples for common atoms like Carbon-12 or Oxygen-16.
Click Calculate
Press the Calculate button to instantly see the number of protons, neutrons, electrons, and additional atomic properties.
Review the Results
Examine the detailed breakdown including isotope notation, electron configuration, and element information. Use this for homework, lab work, or studying.
🔬 What is an Atom?
An atom is the smallest unit of matter that retains all the chemical properties of an element. The word "atom" comes from the Greek word "atomos," meaning indivisible—though we now know atoms are made of even smaller particles called subatomic particles.
📌 Key Definition
An atom consists of three types of subatomic particles:
- Protons (p⁺): Positively charged, located in the nucleus, mass ≈ 1.007 u
- Neutrons (n⁰): No charge (neutral), located in the nucleus, mass ≈ 1.009 u
- Electrons (e⁻): Negatively charged, orbit the nucleus, mass ≈ 0.00055 u
The Structure of an Atom
Atoms have two main regions: the nucleus at the center, which contains protons and neutrons (collectively called nucleons), and the electron cloud surrounding the nucleus where electrons are found.
Nucleus
Contains 99.9% of the atom's mass. Made of protons and neutrons held together by the strong nuclear force.
Electron Cloud
Region where electrons are likely to be found. Electrons exist in energy levels called shells and orbitals.
Protons Define Identity
The number of protons determines which element an atom is. Carbon always has 6 protons; oxygen always has 8.
Electrical Neutrality
In neutral atoms, protons = electrons, balancing positive and negative charges. Ions have unequal numbers.
🔢 Atomic Number vs. Mass Number
Two fundamental numbers define every atom: the atomic number (Z) and the mass number (A). Understanding the difference between these is essential for chemistry calculations.
🔵 Atomic Number (Z)
- Number of protons in the nucleus
- Defines which element the atom is
- Found on the periodic table
- Never changes for a given element
- Example: All carbon atoms have Z = 6
🟢 Mass Number (A)
- Total of protons + neutrons
- Varies between isotopes
- Always a whole number
- Written as superscript (e.g., ¹²C)
- Example: Carbon-12 has A = 12; Carbon-14 has A = 14
Key Formulas
Where: A = Mass number, Z = Atomic number (protons), N = Number of neutrons
Rearranged to find neutrons: Neutrons = Mass number - Atomic number
💡 Example: Iron-56
Given: Iron (Fe) has atomic number 26, and we're looking at the isotope Iron-56
- Protons: Z = 26 (from periodic table)
- Mass number: A = 56 (given)
- Neutrons: N = A - Z = 56 - 26 = 30 neutrons
- Electrons: 26 (same as protons for neutral atom)
☢️ Understanding Isotopes
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.
Why Isotopes Matter
- Same chemical properties (same number of electrons)
- Different physical properties (different masses)
- Some isotopes are stable; others are radioactive
- Used in medicine, dating, and research
Common Isotopes Examples
| Element | Isotope | Protons | Neutrons | Stability | Uses |
|---|---|---|---|---|---|
| Hydrogen | ¹H (Protium) | 1 | 0 | Stable | Most common form |
| Hydrogen | ²H (Deuterium) | 1 | 1 | Stable | Heavy water, NMR |
| Hydrogen | ³H (Tritium) | 1 | 2 | Radioactive | Fusion research |
| Carbon | ¹²C | 6 | 6 | Stable | 98.9% of carbon |
| Carbon | ¹³C | 6 | 7 | Stable | NMR spectroscopy |
| Carbon | ¹⁴C | 6 | 8 | Radioactive | Carbon dating |
| Uranium | ²³⁵U | 92 | 143 | Radioactive | Nuclear fuel |
| Uranium | ²³⁸U | 92 | 146 | Radioactive | 99.3% of uranium |
Isotope Notation
Isotopes are written using the format AZX, where A is the mass number, Z is the atomic number, and X is the element symbol. Since Z is redundant (the symbol tells us the element), it's often omitted: ¹⁴C or Carbon-14.
🔌 Ions: Charged Atoms
An ion is an atom or molecule that has gained or lost one or more electrons, giving it a net electrical charge. Unlike neutral atoms where protons equal electrons, ions have an imbalance.
➕ Cations (Positive Ions)
- Formed when atoms lose electrons
- Protons > Electrons
- Typically metals (Na⁺, Ca²⁺, Fe³⁺)
- Attracted to negative electrodes
- Often achieve noble gas configuration
➖ Anions (Negative Ions)
- Formed when atoms gain electrons
- Electrons > Protons
- Typically nonmetals (Cl⁻, O²⁻, N³⁻)
- Attracted to positive electrodes
- Fill outer electron shell
Calculating Electrons in Ions
Examples:
- Na⁺: 11 protons - (+1) charge = 10 electrons
- Cl⁻: 17 protons - (-1) charge = 18 electrons
- Ca²⁺: 20 protons - (+2) charge = 18 electrons
- O²⁻: 8 protons - (-2) charge = 10 electrons
Isoelectronic Species
Isoelectronic species are atoms or ions that have the same number of electrons. For example, Ne, Na⁺, Mg²⁺, Al³⁺, F⁻, O²⁻, and N³⁻ all have 10 electrons and are isoelectronic with neon.
| Species | Protons | Electrons | Charge | Isoelectronic With |
|---|---|---|---|---|
| Na⁺ | 11 | 10 | +1 | Neon (Ne) |
| Mg²⁺ | 12 | 10 | +2 | Neon (Ne) |
| F⁻ | 9 | 10 | -1 | Neon (Ne) |
| O²⁻ | 8 | 10 | -2 | Neon (Ne) |
| K⁺ | 19 | 18 | +1 | Argon (Ar) |
| Cl⁻ | 17 | 18 | -1 | Argon (Ar) |
⚡ Electron Configuration
The electron configuration describes how electrons are distributed among the various atomic orbitals of an atom. Understanding electron configuration is key to predicting chemical behavior and bonding.
📌 The Aufbau Principle
Electrons fill orbitals starting from the lowest energy level. The order of filling is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s → 5f → 6d → 7p
Orbital Capacity
s Orbitals
Spherical shape. Each s subshell holds 2 electrons. One orbital per subshell.
p Orbitals
Dumbbell shape. Each p subshell holds 6 electrons. Three orbitals per subshell.
d Orbitals
Complex shapes. Each d subshell holds 10 electrons. Five orbitals per subshell.
f Orbitals
Very complex shapes. Each f subshell holds 14 electrons. Seven orbitals per subshell.
Examples of Electron Configurations
| Element | Z | Full Configuration | Noble Gas Notation | Valence e⁻ |
|---|---|---|---|---|
| Hydrogen | 1 | 1s¹ | 1s¹ | 1 |
| Carbon | 6 | 1s² 2s² 2p² | [He] 2s² 2p² | 4 |
| Oxygen | 8 | 1s² 2s² 2p⁴ | [He] 2s² 2p⁴ | 6 |
| Sodium | 11 | 1s² 2s² 2p⁶ 3s¹ | [Ne] 3s¹ | 1 |
| Chlorine | 17 | 1s² 2s² 2p⁶ 3s² 3p⁵ | [Ne] 3s² 3p⁵ | 7 |
| Iron | 26 | 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ | [Ar] 4s² 3d⁶ | 2 (or 8) |
⚠️ Exceptions to the Rules
Some elements have unexpected electron configurations due to the stability of half-filled or fully-filled d orbitals:
- Chromium (Z=24): [Ar] 4s¹ 3d⁵ (not 4s² 3d⁴)
- Copper (Z=29): [Ar] 4s¹ 3d¹⁰ (not 4s² 3d⁹)
⚖️ Atomic Mass: Calculation and Concepts
Atomic mass (also called atomic weight) is the mass of an atom, typically expressed in atomic mass units (u) or daltons (Da). Understanding the difference between atomic mass and mass number is crucial for chemistry.
Mass Number (A)
- Whole number only
- Simply counts protons + neutrons
- Specific to one isotope
- Example: Carbon-12 has A = 12
Atomic Mass
- Precise decimal value
- Accounts for binding energy
- Average of all isotopes (weighted)
- Example: Carbon's atomic mass = 12.011 u
Calculating Atomic Mass
Where:
- mp = proton mass = 1.007276 u
- mn = neutron mass = 1.008665 u
- me = electron mass = 0.000549 u
Mass Defect and Binding Energy
The actual atomic mass is slightly less than the sum of its parts. This difference is called the mass defect and corresponds to the binding energy holding the nucleus together (E = mc²).
💡 Example: Helium-4 Mass Defect
Expected mass: 2(1.007276) + 2(1.008665) + 2(0.000549) = 4.032980 u
Actual mass: 4.002602 u
Mass defect: 4.032980 - 4.002602 = 0.030378 u
This "missing" mass has been converted to binding energy!
🔬 Subatomic Particle Properties
Understanding the properties of protons, neutrons, and electrons is fundamental to atomic physics and chemistry. Here's a comprehensive comparison:
| Property | Proton (p⁺) | Neutron (n⁰) | Electron (e⁻) |
|---|---|---|---|
| Charge | +1 (+1.602×10⁻¹⁹ C) | 0 | -1 (-1.602×10⁻¹⁹ C) |
| Mass (u) | 1.007276 | 1.008665 | 0.000549 |
| Mass (kg) | 1.673×10⁻²⁷ | 1.675×10⁻²⁷ | 9.109×10⁻³¹ |
| Location | Nucleus | Nucleus | Electron cloud |
| Discovered by | Rutherford (1917) | Chadwick (1932) | Thomson (1897) |
| Quark composition | uud | udd | Fundamental particle |
| Stability (free) | Stable | ~10 min half-life | Stable |
📌 Key Insights
- Protons are ~1836 times heavier than electrons
- Neutrons are slightly heavier than protons (by about 0.14%)
- The electron mass is often neglected in atomic mass calculations
- Free neutrons decay into protons, electrons, and antineutrinos via beta decay
❌ 6 Common Mistakes in Atom Calculations
Even experienced students make these errors. Avoid these common pitfalls when calculating atomic properties:
Confusing Z and A
Atomic number (Z) is protons only. Mass number (A) is protons + neutrons. Remember: Z defines the element; A defines the isotope.
Wrong Sign for Ions
Electrons = Z - charge. For Ca²⁺: 20 - (+2) = 18 electrons. For Cl⁻: 17 - (-1) = 18 electrons. Watch the signs!
Mass Number ≠ Atomic Mass
Mass number is a whole number count. Atomic mass is a precise measurement including binding energy effects and isotope averaging.
Using Average Mass for Isotopes
When working with specific isotopes (like C-14), use the mass number, not the average atomic mass from the periodic table.
Forgetting Isotopes Exist
The same element can have different neutron counts. Carbon-12 and Carbon-14 are both carbon but have different properties.
Electron Config Filling Order
4s fills before 3d! Follow the Aufbau principle carefully. Use the diagonal rule or memorize the sequence.
🌍 Real-World Applications
Understanding atomic structure isn't just academic—it has crucial applications in many fields:
🏥 Medicine and Healthcare
- Medical Imaging: Radioactive isotopes (Tc-99m, I-131) for PET and SPECT scans
- Cancer Treatment: Radiation therapy using Co-60, Cs-137
- Diagnostics: Radioactive tracers to study organ function
- MRI: Based on hydrogen nuclei behavior in magnetic fields
🏛️ Archaeology and Geology
- Carbon Dating: C-14 decay measures age up to 50,000 years
- Rock Dating: K-Ar, Rb-Sr, U-Pb dating for geological timescales
- Forensics: Isotope ratios reveal geographic origin
⚡ Energy and Industry
- Nuclear Power: U-235 fission in reactors
- Fusion Research: Deuterium and tritium fusion
- Smoke Detectors: Am-241 alpha particle ionization
- Food Preservation: Gamma irradiation using Co-60
🔬 Research and Chemistry
- NMR Spectroscopy: Uses specific isotopes (¹H, ¹³C) for molecular structure
- Mass Spectrometry: Identifies compounds by atomic mass
- Tracer Studies: Track biochemical pathways with isotope labels
✅ Expert Review and Sources
This calculator and accompanying content were developed based on established principles of atomic physics and chemistry. Our calculation methods align with those used in academic institutions and standardized by international scientific organizations.
Methodology
- Atomic data from IUPAC (International Union of Pure and Applied Chemistry)
- Particle masses from NIST (National Institute of Standards and Technology)
- Electron configurations following IUPAC recommendations
- Periodic table data updated to include all 118 elements
Accuracy
Calculations use JavaScript floating-point arithmetic. Atomic masses are accurate to the values published in IUPAC's standard atomic weights. For critical scientific applications, consult primary literature sources.
This tool is designed for educational purposes. For research applications requiring high precision, verify results with authoritative databases.
📚 Sources and References
- IUPAC Periodic Table of Elements
- NIST Atomic Weights and Isotopic Compositions
- PubChem Periodic Table
- Chang, R.: Chemistry (13th Edition), McGraw-Hill
- Zumdahl, S.S.: Chemical Principles (8th Edition), Cengage
❓ People Also Ask
How do I find the number of protons in an atom?
The number of protons equals the atomic number (Z), which you can find on the periodic table. Every element has a unique atomic number. For example, oxygen always has 8 protons (Z=8), gold always has 79 protons (Z=79). The atomic number defines what element an atom is.
What is the difference between atoms and ions?
Atoms are electrically neutral—they have equal numbers of protons and electrons. Ions are atoms that have gained or lost electrons, creating a net charge. Cations are positive (lost electrons); anions are negative (gained electrons). For example, Na has 11 protons and 11 electrons, but Na⁺ has 11 protons and only 10 electrons.
Why do isotopes have different masses?
Isotopes of the same element have the same number of protons but different numbers of neutrons. Since neutrons contribute to mass (≈1 u each), more neutrons means greater mass. Carbon-12 has 6 neutrons; Carbon-14 has 8 neutrons, making it about 17% heavier.
Can atoms have no neutrons?
Yes! Protium (¹H), the most common isotope of hydrogen, has 1 proton and 0 neutrons. It's the only stable atom without neutrons. Heavier elements need neutrons for nuclear stability—without them, the positive protons would repel each other and the nucleus would fly apart.
How do electrons determine chemical properties?
Chemical properties depend on valence electrons (outermost shell). Elements with similar valence electron configurations behave similarly—that's why the periodic table is organized in groups. Sodium (1 valence electron) and potassium (1 valence electron) both readily form +1 ions.
What are valence electrons?
Valence electrons are the electrons in the outermost (highest energy) shell of an atom. They participate in chemical bonding. For main group elements, the group number often equals the number of valence electrons: Group 1 has 1 valence electron, Group 17 has 7 valence electrons.
📋 Frequently Asked Questions
Use the formula: Neutrons = Mass Number (A) - Atomic Number (Z). Find the atomic number on the periodic table, and the mass number from the isotope notation (e.g., the "14" in Carbon-14). For ¹⁴C: 14 - 6 = 8 neutrons.
Atomic mass is typically expressed in atomic mass units (u), where 1 u = 1.66054×10⁻²⁷ kg. A carbon-12 atom has a mass of exactly 12 u by definition, or about 1.99×10⁻²⁶ kg. To convert u to kg, multiply by 1.66054×10⁻²⁷.
In a neutral atom, the number of electrons equals the number of protons (which equals the atomic number). This balance of positive and negative charges makes the atom electrically neutral. Oxygen (Z=8) has 8 protons and 8 electrons when neutral.
Nuclear stability depends on the ratio of neutrons to protons. Light elements are stable with N ≈ Z; heavier elements need more neutrons. The "band of stability" shows stable combinations. Too many or too few neutrons makes atoms radioactive—they decay to reach a more stable configuration.
The atomic number (number of protons) uniquely identifies each element. Elements are arranged in order of increasing atomic number. This organization reveals periodic patterns in properties: elements in the same column (group) have similar chemical behaviors because they have the same number of valence electrons.
Electron configuration shows how electrons are distributed in orbitals (1s, 2s, 2p, etc.). It determines chemical properties and bonding behavior. Atoms with similar outer (valence) electron configurations have similar properties—this is why the periodic table groups work.
Yes! When an atom loses electrons, it becomes a positive ion (cation) with more protons than electrons. For example, Na⁺ has 11 protons but only 10 electrons. Metals commonly form cations by losing their valence electrons.
Full isotope notation is ᴬ꜀X, where A is mass number (superscript), Z is atomic number (subscript), and X is the element symbol. Since Z is implied by the symbol, it's often written as just ᴬX or Element-A. Examples: ¹⁴C, ²³⁵U, or Carbon-14, Uranium-235.
The atomic mass unit (u), also called dalton (Da), is defined as exactly 1/12 the mass of a carbon-12 atom. This equals approximately 1.66054×10⁻²⁷ kg. Using u makes atomic-scale masses manageable numbers instead of tiny decimals.
Radioactivity occurs when a nucleus is unstable due to an unfavorable proton-to-neutron ratio or being too large. The nucleus spontaneously emits particles (alpha, beta) or energy (gamma rays) to become more stable. All elements with Z > 82 (lead) are radioactive.