Atomic number 1 is hydrogen, the simplest atom. Atomic number 118 is oganesson, an artificial atom that has only been observed in single-atom quantities.
How to Play: Guess if the element on the right has a HIGHER or LOWER atomic number than the one on the left.
Name A
Name B
Top 10 Highest-Numbered Elements
An element’s atomic number is the count of protons in its nucleus. It determines the element’s identity and its position on the periodic table. From hydrogen (1) to oganesson (118), every element has a unique number.
| # | Name | Atomic Number | Unit |
|---|---|---|---|
| 1 | Oganesson | 118 | |
| 2 | Tennessine | 117 | |
| 3 | Livermorium | 116 | |
| 4 | Moscovium | 115 | |
| 5 | Flerovium | 114 | |
| 6 | Nihonium | 113 | |
| 7 | Copernicium | 112 | |
| 8 | Roentgenium | 111 | |
| 9 | Plutonium | 94 | |
| 10 | Uranium | 92 |
How the Periodic Table Is Numbered
Atomic number defines an element. Hydrogen has 1 proton, helium has 2, and so on through the entire periodic table. Add or remove a proton and the element changes — bombard hydrogen with a proton at high enough energy and you can convert it into helium (this is what powers the Sun).
Elements 1-92 (hydrogen to uranium) occur naturally on Earth. Elements 93-118 are synthetic, created in particle accelerators by smashing lighter atoms together. Most synthetic elements exist for fractions of a second before decaying — only a single atom or small cluster has ever existed for many of them.
Element 118, oganesson, was first synthesized in 2002 at the Joint Institute for Nuclear Research in Russia. Its half-life is under 1 millisecond. Element 119, theoretically the next discovery, has never been confirmed despite multiple synthesis attempts. The current periodic table ends at 118.
Frequently Asked Questions
What's the highest atomic number?
118 (oganesson). It is the heaviest element ever synthesized, with a half-life of less than 1 millisecond.
What's the difference between mass number and atomic number?
Atomic number counts only protons. Mass number counts protons plus neutrons. Iron (26 protons, 30 neutrons) has atomic number 26 and mass number 56.
Are there elements heavier than uranium in nature?
Trace amounts of plutonium (94) and neptunium (93) occur naturally from neutron capture in uranium ores. Beyond that, all are synthetic.
Can new elements still be discovered?
Synthesis attempts for elements 119 and 120 have been ongoing since the 2000s but neither has been confirmed. The ‘island of stability’ hypothesis predicts some superheavy elements may have longer half-lives, but no confirmed example exists yet.
Note: Atomic numbers are absolute physical properties; values do not change. Element discovery dates and properties can be found at IUPAC.org.
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