This chart ranks the heaviest naturally occurring chemical elements by standard atomic mass, in atomic mass units. All are radioactive and all sit at the far end of the periodic table among the actinides and heavy metals.

About: Heaviest Naturally Occurring Elements by Atomic Mass

Overview of the data behind this chart

AI Insight

Uranium is the heaviest naturally occurring element in significant quantity, with an atomic mass near 238, followed closely by thorium (232) and protactinium (231). Every element on this list is radioactive, and most, including actinium, radium, francium, radon, astatine and polonium, exist in nature only as fleeting decay products of uranium and thorium. Their atomic masses cluster tightly between 209 and 238, reflecting how the periodic table effectively runs out of stable nuclear configurations at this end. Bismuth (209), long regarded as the heaviest stable element, is now known to be very faintly radioactive, with a half-life vastly longer than the age of the universe. Beyond uranium lie only the synthetic transuranium elements such as plutonium and americium, produced in reactors and particle accelerators rather than found in nature.

Data source: IUPAC Standard Atomic Weights

Key Findings

Auto-computed highlights from this dataset

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Uranium leads with 238 in All Time.

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Average value in All Time: 223 · median: 225.

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Gap in All Time: Uranium is 1.1× larger than Bismuth.

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Heaviest Naturally Occurring Elements by Atomic Mass

Data Insights Below

Data Insights

Numbers, trends & sources behind this chart

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Data Points

10 categories · 1 year

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Top Value

238.03

Uranium

Standard Atomic Mass (u) · All Time

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Metrics

Standard Atomic Mass (u)

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Period

All Time

Single year snapshot

Category Rankings

Standard Atomic Mass (u) · All Time

#	Category	All Time
🥇	Uranium	238.03
🥈	Thorium	232.04
🥉	Protactinium	231.04
4	Actinium	227
5	Radium	226
6	Francium	223
7	Radon	222
8	Astatine	210
9	Polonium	209
10	Bismuth	208.98

Statistical Summary — Standard Atomic Mass (u) · All Time

238.03

Maximum

208.98

Minimum

223

Average

225

Median

What This Data Shows

Auto-generated trend summaries per category

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Uranium

Recorded 238.03 Standard Atomic Mass (u) in All Time.

Source

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Thorium

Recorded 232.04 Standard Atomic Mass (u) in All Time.

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Protactinium

Recorded 231.04 Standard Atomic Mass (u) in All Time.

Source

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Actinium

Recorded 227 Standard Atomic Mass (u) in All Time.

Source

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Radium

Recorded 226 Standard Atomic Mass (u) in All Time.

Source

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Francium

Recorded 223 Standard Atomic Mass (u) in All Time.

Source

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Radon

Recorded 222 Standard Atomic Mass (u) in All Time.

Source

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Astatine

Recorded 210 Standard Atomic Mass (u) in All Time.

Source

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Polonium

Recorded 209 Standard Atomic Mass (u) in All Time.

Source

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Bismuth

Recorded 208.98 Standard Atomic Mass (u) in All Time.

Source

Full Data Table

10 records across 1 year

10 sourced

Category	Metric	All Time
Uranium	Standard Atomic Mass (u)	238.03
Thorium	Standard Atomic Mass (u)	232.04
Protactinium	Standard Atomic Mass (u)	231.04
Actinium	Standard Atomic Mass (u)	227
Radium	Standard Atomic Mass (u)	226
Francium	Standard Atomic Mass (u)	223
Radon	Standard Atomic Mass (u)	222
Astatine	Standard Atomic Mass (u)	210
Polonium	Standard Atomic Mass (u)	209
Bismuth	Standard Atomic Mass (u)	208.98