Actinium
ACTINOID · GROUP None · PERIOD 7
89
Ac
Actinium
227
Atomic Data
| Atomic Number | 89 |
| Symbol | Ac |
| Atomic Weight | 227 u |
| Density (STP) | 10.07 g/cm³ |
| Melting Point | 1049.85 °C (1323 K) |
| Boiling Point | 3197.85 °C (3471 K) |
| Electronegativity | 1.1 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Actinoid |
| Period / Group | 7 / None |
| CAS Number | 7440-34-8 |
Electron Configuration
{{BOHR_SVG}}
[Rn] 6d1 7s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 2 | 80 |
| P | 6 | 6p | 6 | 86 |
| P | 6 | 6d | 1 | 87 |
| Q | 7 | 7s | 2 | 89 |
| Total | 89 | 89 | ||
Isotopes of Actinium
Actinium is monoisotopic — ²²⁷Ac is its only naturally occurring stable isotope, accounting for 100% of all natural Actinium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Actinium-227 | ²²⁷Ac | 89 | 138 | trace | Stable |
Abundance & Occurrence
Actinium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Actinium
None ppm
Silicon (ref.)
277,000 ppm
Oxygen (ref.)
461,000 ppm
Universe (ppm by mass)
Actinium
None ppm
Helium (ref.)
230,000 ppm
Hydrogen (ref.)
739,000 ppm
Discovery & History
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Safety & Handling
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Actinium in the Real World
Real-World Uses
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Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.