The heaviest known element has 294 times the mass of hydrogen. Both are technically just protons, neutrons, and electrons.
How to Play: Guess if the element on the right has a HIGHER or LOWER atomic mass than the one on the left.
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Top 10 Heaviest Elements
Atomic mass in amu (atomic mass units = roughly grams per mole). Includes protons, neutrons, and a tiny electron contribution.
| # | Name | Atomic Mass (amu) | Unit |
|---|---|---|---|
| 1 | Oganesson (Og) | 294 | amu |
| 2 | Tennessine (Ts) | 294 | amu |
| 3 | Livermorium (Lv) | 293 | amu |
| 4 | Moscovium (Mc) | 290 | amu |
| 5 | Flerovium (Fl) | 289 | amu |
| 6 | Nihonium (Nh) | 286 | amu |
| 7 | Copernicium (Cn) | 285 | amu |
| 8 | Roentgenium (Rg) | 282 | amu |
| 9 | Darmstadtium (Ds) | 281 | amu |
| 10 | Meitnerium (Mt) | 278 | amu |
Atomic Mass Origins
Atomic mass is dominated by protons + neutrons. Each amu is roughly 1.66×10⁻²⁷ kg. The unit is defined as 1/12 the mass of a carbon-12 atom.
Hydrogen (1.008 amu) has 1 proton, 0 neutrons typically. Heavier elements add nucleons: oganesson has 118 protons + 176 neutrons.
Synthetic elements (atomic numbers 95+) exist briefly. Their reported masses are estimates from production decay chains, not direct measurements.
Frequently Asked Questions
Heaviest element?
Oganesson at 294 amu — though it exists for less than 1 millisecond before decaying.
Is atomic mass the same as atomic weight?
Same concept; ‘atomic weight’ is the standard term for chemistry, ‘atomic mass’ for physics. Numbers identical.
Why are isotope masses fractional?
An element’s standard atomic mass averages all naturally-occurring isotopes by abundance. Hydrogen’s 1.008 reflects ~99.985% H-1 + 0.015% deuterium.
Could heavier elements exist?
Possibly — the ‘island of stability’ theory predicts some superheavy isotopes might be relatively long-lived. None confirmed yet.
Note: Atomic masses in amu per IUPAC 2024.
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