Atomic Number Table
A complete, interactive directory of all 118 chemical elements. Sort, search, and explore properties like atomic mass, electron configuration, and element categories.
What is an Atomic Number?
The atomic number (represented by the symbol Z) is the defining property of a chemical element. It signifies the total number of protons found in the nucleus of an atom.
Because atoms are electrically neutral in their standard state, the atomic number also tells you the number of electrons surrounding the nucleus. This electron count effectively determines the element's chemical behavior.
Why is it Important?
- Identity: Converting Hydrogen into Helium requires changing the proton count. Chemical reactions never change the atomic number; only nuclear reactions do.
- Sorting: It is the primary method for ordering the Periodic Table. Elements list from 1 (H) to 118 (Og).
- Properties: Z determines the electronic structure, which dictates bonding, phase, and color.
Atomic Number vs. Mass Number
| Property | Atomic Number (Z) | Mass Number (A) |
|---|---|---|
| Definition | Number of Protons | Protons + Neutrons |
| Values | Always a whole number (e.g., 6) | Also a whole number (e.g., 12, 13, 14) |
| Isotopes | Same for all isotopes | Differs between isotopes |
| Periodic Table | Elements sorted by this | Generally increases with Z |
Frequently Asked Questions
Frequently Asked Questions
What uses the atomic number to organize elements?
The periodic table uses the atomic number (number of protons) to organize elements in ascending order. This unique number determines the element's identity.
Which element has atomic number 1?
Hydrogen (H) is the first element with atomic number 1, meaning it has one proton in its nucleus.
What is the highest atomic number?
Currently, the highest atomic number is 118, which belongs to Oganesson (Og), a synthetic noble gas.
How is atomic number different from atomic mass?
Atomic number (Z) is the number of protons and is always a whole number. Atomic mass (A) is the weighted average mass of an element's isotopes (protons + neutrons) and is usually a decimal.
Do isotopes have different atomic numbers?
No. All isotopes of an element have the SAME atomic number (same number of protons) but different mass numbers (different number of neutrons).
Who discovered the concept of atomic number?
Henry Moseley, a British physicist, established the physical basis of the atomic number in 1913, showing it was related to the charge of the nucleus.
Can two elements have the same atomic number?
No. The atomic number is the unique "fingerprint" of an element. If the number of protons changes, it becomes a different element.
How do I use this table?
You can use the search bar to find elements by name ("Gold"), symbol ("Au"), or number ("79"). Toggle between "Grid" and "List" views to see data in your preferred format.
What categories are included?
The table allows filtering by categories such as Alkali Metals, Noble Gases, Transition Metals, Halogens, and more.
Is this list up to date?
Yes, this list includes all validated elements up to 118 (Oganesson) as recognized by IUPAC.