Element / isotope identity
Element 89, 227Ac decay-series identity and reference phase values are evaluated.
Metal structure
The FCC metallic reference is evidence-limited by scarcity/radioactivity and is presented cautiously.
225Ac medical context
Targeted-alpha context is high-level and excludes isotope production, source preparation, dose or handling instructions.
Safety boundary
No operational radioactive-material guidance is provided.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Actinium (Ac)
Actinium is element 89, a scarce radioactive actinide whose best-established chemistry is +3. Natural ²²⁷Ac occurs in the ²³⁵U decay series, while ²²⁵Ac has become important in targeted-alpha-therapy research under tightly controlled medical/nuclear systems.
Actinium atomic number, mass, electron configuration and key properties
Actinium: quick answers
How many protons, neutrons and electrons does actinium have?
Actinium’s atomic number is 89, so every actinium atom has 89 protons, and a neutral atom also has 89 electrons. Actinium has no stable isotopes, so the neutron count depends on the isotope: actinium-227, featured on this page, has 138 neutrons.
What is the symbol for actinium?
The chemical symbol for actinium is Ac.
Is actinium a solid, liquid or gas at room temperature?
Actinium is a solid at room temperature (about 25 °C).
What family (group) is actinium in?
Actinium is an actinide, in group 3, period 7 of the periodic table.
What is the electron configuration of actinium?
The ground-state electron configuration of actinium is [Rn] 6d¹ 7s².
From atomic number to chemistry
Read these as a chain of causes, not as isolated facts. Each step links to the concept hub if you want the underlying idea explained.
89 protons define actinium.
The reference ground-state configuration frames atomic and chemical behavior.
Periodic position organizes recurring trends without replacing element-specific evidence.
The teaching nucleus is one isotope, not the relative atomic mass.
Phase claims are evidence-labelled; unknown superheavy bulk boundaries are not fabricated.
Actinium in its period and family
Actinium begins the actinide series conceptually and sits in Period 7. Its electron configuration and +3 chemistry connect it to neighboring early actinides.
Actinium Visual Lab
Compare Ac with Ac³⁺, inspect a ²²⁷Ac teaching nucleus and 7s/6d probability models, view the reported metallic structure cautiously, then connect decay-series occurrence, discovery history and high-level ²²⁵Ac research.
Every mark points to one exact feature
The numbered markers explain the same information system used throughout Element Lookup. Unknown or predicted fields remain visibly labelled rather than being replaced with guesses.
Actinium in one minute
Atomic number 89 means 89 protons.
The reference configuration is [Rn] 6d¹ 7s².
Actinium commonly forms +3 chemistry.
²²⁷Ac occurs naturally in the ²³⁵U decay series.
²²⁵Ac is researched/used in specialized targeted-alpha medical contexts; this does not make actinium a general-purpose material.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 32 · 18 · 9 · 2 electrons
The 7s and representative 6d probability models are isolated-atom teaching approximations. They do not show radioactive decay or the electronic bands of bulk actinium.
Bulk actinium measurements are difficult because the element is scarce and radioactive. The material viewer uses the reported face-centred-cubic metallic reference with an evidence note rather than implying abundant bulk samples.. The viewer is evidence-aware: measured structures are identified as such; unknown bulk structures stay unknown.
Teaching visualization; not a literal finite sample or thermal trajectory.What this model does—and does not—show
The 7s and representative 6d probability models are isolated-atom teaching approximations. They do not show radioactive decay or the electronic bands of bulk actinium.
Where do I meet actinium?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Decay-series occurrence
Trace ²²⁷Ac occurs naturally as part of the ²³⁵U decay chain.
227Ac decay-series isotope vs 225Ac medical research
Actinium’s most important distinctions are nuclear: isotope identity changes decay behavior and scientific application.
Natural decay-series context
227Ac occurs in trace amounts in the 235U decay series.
Radium, actinium and thorium
Actinium sits at the transition from alkaline-earth radium into the actinide series.
| Z | 88 |
|---|---|
| Common ion | Ra²⁺ |
| Z | 89 |
|---|---|
| Common ion | Ac³⁺ |
| Z | 90 |
|---|---|
| Important state | Th⁴⁺ |
Actinium properties: atomic, physical, thermal and chemical
Categories follow the science of this element rather than a fixed decorative template. Each row carries condition/provenance context and an evidence label; unknown values stay unknown.
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Atomic number | 89 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | [227] | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Rn] 6d¹ 7s² | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group Actinides · Period 7 · d-block | Periodic-table placement | Evaluated |
| Electronegativity | 1.1 (approx.) | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ²²⁷Ac | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Radioactive silvery-white solid | Source-reviewed; see Sources below | Evaluated |
| Density | 10 g/cm³ | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Actinium metal · reported FCC teaching reference | Bulk actinium measurements are difficult because the element is scarce and radioactive. The material viewer uses the reported face-centred-cubic metallic reference with an evidence note rather than implying abundant bulk samples. | Measured |
| Classification | Actinide | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Bulk actinium measurements are difficult because the element is scarce and radioactive. The material viewer uses the reported face-centred-cubic metallic reference with an evidence note rather than implying abundant bulk samples. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 1323 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 3473 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | Using evaluated reference values, actinium is treated as solid below about 1323 K, liquid to about 3473 K and gas above. Scarcity/radioactivity make bulk-property evidence less abundant than for common metals. | Shared phase registry drives the slider, regions and markers. | Evaluated |
| Condition warning | Temperature and pressure define phase behavior; purity/allotropy may matter. | Teaching condition statement | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Common oxidation states | +3 | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Ac³⁺ | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Actinium begins the actinide series conceptually and sits in Period 7. Its electron configuration and +3 chemistry connect it to neighboring early actinides. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ²²⁷Ac | Radioactive · natural decay-series isotope | Reference teaching nucleus: 89 protons and 138 neutrons. | Evaluated |
| ²²⁵Ac | Radioactive · targeted-alpha medical research/therapy | A high-interest isotope used in highly regulated radiopharmaceutical contexts. | Evaluated |
| ²²⁸Ac | Short-lived radioactive isotope | Appears in the ²³²Th decay series and is important in decay-series measurements. | Evaluated |
| Teaching nucleus | ²²⁷Ac · 89 protons + 138 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Element identity, isotope data and reference phase values are evaluated. The metallic structure is evidence-limited and labelled as a reported teaching reference. Medical/nuclear context stays non-operational. | Evidence summary for this guide | Reviewed |
| Structure evidence | Bulk actinium measurements are difficult because the element is scarce and radioactive. The material viewer uses the reported face-centred-cubic metallic reference with an evidence note rather than implying abundant bulk samples. | Measured structure, labelled schematic, prediction or explicit unknown as applicable. | Reviewed |
| Map evidence rule | Real pins are reviewed examples; conceptual layers are used when pins would mislead. | Geography Explorer 2.0 | Reviewed |
| Source set | 3 primary/reference links listed below | Open the Sources section for the actual references. | Reviewed |
Is Actinium a solid, liquid or gas? State at temperature
Using evaluated reference values, actinium is treated as solid below about 1323 K, liquid to about 3473 K and gas above. Scarcity/radioactivity make bulk-property evidence less abundant than for common metals.
Where on Earth is Actinium found or produced?
Who discovered Actinium, and when?
André Debierne reported a new radioactive element from pitchblende residues in Paris.
Friedrich Giesel independently isolated the element and described its strong radioactivity.
Actinium became important mainly in nuclear/radiochemical research.
²²⁵Ac is an important radionuclide in targeted-alpha therapy research and clinical development under regulated systems.
Actinium isotope context: occurrence, research and regulated use
Natural ²²⁷Ac appears only in trace amounts within the ²³⁵U decay series.
Research/medical isotopes such as ²²⁵Ac are produced only in specialized nuclear facilities; no production route is described here.
Radiochemical purification, source preparation and clinical formulation require licensed infrastructure and are outside this educational page.
The science focus here is isotope identity, decay context, chemistry and evidence—not operational handling.
What is actinium used for?
Targeted-alpha research
²²⁵Ac is used in regulated targeted-alpha radiopharmaceutical research/therapy contexts.
Nuclear research
Actinium isotopes support specialized nuclear/radiochemical studies.
Source science
Strong alpha-emitting isotopes provide controlled research sources; no source-construction guidance is given.
Historical radiochemistry
Actinium is central to the history of radioactivity and the actinide concept.
Actinium isotopes and natural abundance
²²⁷Ac
Radioactive · natural decay-series isotopeReference teaching nucleus: 89 protons and 138 neutrons.
²²⁵Ac
Radioactive · targeted-alpha medical research/therapyA high-interest isotope used in highly regulated radiopharmaceutical contexts.
²²⁸Ac
Short-lived radioactive isotopeAppears in the ²³²Th decay series and is important in decay-series measurements.
Five-question Actinium check
What is actinium’s atomic number?
What is the common actinium oxidation state?
Which isotope is prominent in targeted-alpha research?
Where does natural ²²⁷Ac occur?
What is excluded from this guide?
Actinium questions students commonly ask
Each answer starts with the direct fact, then explains the chemistry, evidence or material context so the result is understandable rather than merely memorized.
What is actinium’s atomic number?
Short answer: 89.
Atomic number is defined by proton count, so 89 protons are what make an atom actinium. A neutral actinium atom also has 89 electrons, while isotopes can have different neutron counts without changing the element.
Key point: Atomic number = proton count.
Is actinium a metal?
Short answer: Yes. It is a radioactive actinide metal.
This guide classifies Actinium as an actinide. Its periodic position is Period 7, d-block, Group Actinides. Actinium begins the actinide series conceptually and sits in Period 7. Its electron configuration and +3 chemistry connect it to neighboring early actinides.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
What is actinium used for?
Short answer: Mostly specialized nuclear research; ²²⁵Ac is important in targeted-alpha radiopharmaceutical research and therapy.
Targeted-alpha research: ²²⁵Ac is used in regulated targeted-alpha radiopharmaceutical research/therapy contexts. Nuclear research: Actinium isotopes support specialized nuclear/radiochemical studies. Actinium’s nuclear isotope story is more prominent than everyday bulk-material use. The page separates natural ²²⁷Ac, medically researched ²²⁵Ac, metallic structure data and safety controls.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Where is actinium found naturally?
Short answer: Trace ²²⁷Ac occurs in uranium ores as part of the ²³⁵U decay series.
Natural ²²⁷Ac appears only in trace amounts within the ²³⁵U decay series. Decay-series occurrence Trace ²²⁷Ac occurs naturally as part of the ²³⁵U decay chain.
Key point: Natural occurrence, resources, production and recycling are different geography questions.
What is the common oxidation state?
Short answer: +3.
Actinium commonly forms +3 chemistry. Using evaluated reference values, actinium is treated as solid below about 1323 K, liquid to about 3473 K and gas above. Scarcity/radioactivity make bulk-property evidence less abundant than for common metals.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Is this page a guide to producing or handling ²²⁵Ac?
Short answer: No. It deliberately excludes production, purification, source preparation and handling procedures.
Actinium isotopes are radioactive. This educational page does not provide production, separation, source fabrication, access, dose, handling or clinical instructions. Safety boundary All isotope production, source handling and clinical use belong in licensed professional systems; this page remains high-level.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Scientific sources for Actinium
- Royal Society of Chemistry - Actinium
- NIST - Atomic Data for Actinium
- IAEA - Actinium-225 / alpha-emitter context
Questions to ask next about Actinium
A good element lesson should lead to the next useful question, not end after a list of facts.
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