Synthetic element

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The chemical elements labeled as synthetic are unstable, with a half-life so short (ranging from a fraction of millisecond to a few million years) relative to the age of the Earth that any atoms of that element that may have been present when the Earth formed have long since completely decayed away. Hence they are only known on Earth as the product of nuclear reactors or particle accelerators.

The first synthetic element created was technetium, which filled a gap in the periodic table, and the discovery that there were no stable isotopes of technetium explained its absence on Earth: its 4.2 million year half-life meant that none remained from the time of formation of the Earth. However, technetium is still naturally present on Earth as a by-product of the decay of uranium-238.

quasi-synthetic elements include:

Technetium, atomic number 43
Promethium, atomic number 61
Astatine, atomic number 85
Francium, atomic number 87
Neptunium, atomic number 93
Plutonium, atomic number 94

(all elements with atomic numbers 1-94 are naturally occurring at least in trace quantities)

Transuranium elements
- Americium symbol Am, atomic number 95
- Curium symbol Cm, atomic number 96
- Berkelium symbol Bk, atomic number 97
- Californium symbol Cf, atomic number 98
- Einsteinium symbol Es, atomic number 99
- Fermium symbol Fm, atomic number 100
- Mendelevium symbol Md, atomic number 101
- Nobelium symbol No, atomic number 102
- Lawrencium symbol Lr, atomic number 103
- Rutherfordium symbol Rf, atomic number 104
- Transactinide elements
  - Dubnium symbol Db, atomic number 105
  - Seaborgium symbol Sg, atomic number 106
  - Bohrium symbol Bh, atomic number 107
  - Hassium symbol Hs, atomic number 108
  - Meitnerium symbol Mt, atomic number 109
  - Darmstadtium symbol Ds, atomic number 110
  - Roentgenium symbol Rg, atomic number 111