Atomic / phase data
Reference atomic and phase values are source-reviewed.
Material structure
The ordinary elemental structure is measured/reviewed; the viewer is a teaching representation.
Element vs material uses
Uses distinguish elemental metal from compounds, alloys, doped hosts or isotope-specific systems.
Geography
Discovery/supply context is selective and does not fabricate deposits, facilities or inventories.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Thulium (Tm)
Thulium is element 69, a rare lanthanide whose Tm³⁺ optical transitions connect the periodic table to near-infrared lasers and specialized isotope applications.
Thulium atomic number, mass, electron configuration and key properties
Thulium: quick answers
How many protons, neutrons and electrons does thulium have?
Thulium’s atomic number is 69, so every thulium atom has 69 protons, and a neutral atom also has 69 electrons. Its most common natural isotope, thulium-169, has 100 neutrons (other isotopes have different neutron counts).
What is the symbol for thulium?
The chemical symbol for thulium is Tm.
Is thulium a solid, liquid or gas at room temperature?
Thulium is a solid at room temperature (about 25 °C).
What family (group) is thulium in?
Thulium is a lanthanide, in period 6 (the f-block row shown below the main table) of the periodic table.
What is the electron configuration of thulium?
The ground-state electron configuration of thulium is [Xe] 4f¹³ 6s².
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.
69 protons define thulium.
The ground-state configuration frames atomic and chemical behavior.
Periodic position organizes recurring chemistry and trends.
The teaching nucleus is one isotope, not the relative atomic mass.
Phase claims preserve source-reviewed evidence and material context.
Thulium in its period and family
Thulium is the penultimate lanthanide, with [Xe]4f¹³6s² ground state. Tm³⁺ dominates ordinary chemistry, while the nearly filled 4f shell produces useful near-infrared optical transitions.
Thulium Visual Lab
Explore Tm across the teaching nucleus, isolated-atom orbitals, evidence-aware material structure and temperature/evidence views, then connect those models to uses, isotopes, search-led questions and source-backed context.
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.
Thulium in one minute
Atomic number 69 means every thulium nucleus has 69 protons.
Neutral Thulium has the ground-state configuration [Xe] 4f¹³ 6s².
The representative teaching isotope is ¹⁶⁹Tm.
Thulium laser materials use Tm ions inside a host crystal or glass.
The ordinary material reference is Hexagonal close-packed (HCP).
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 31 · 8 · 2 electrons
The displayed 4f_xyz orbital is one representative real f cubic harmonic. It is not a picture of the whole 4f subshell or the electronic bands in the bulk material.
Ordinary thulium metal is HCP. Tm-doped laser hosts and isotope source materials have different structures and are kept separate from the elemental lattice.. 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 displayed 4f_xyz orbital is one representative real f cubic harmonic. It is not a picture of the whole 4f subshell or the electronic bands in the bulk material.
Where do I meet thulium?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Near-infrared lasers
Tm³⁺-doped hosts support laser emission near 2 μm and other optical transitions.
4f¹³ → Tm³⁺ → near-2 μm laser materials
Thulium’s signature optical role comes from Tm³⁺ ions in a host. Artificial ¹⁷⁰Tm radioactivity is a separate isotope-specific context.
4f¹³6s²
One 4f vacancy before Yb’s filled 4f shell.
Thulium in periodic context
Compare nearby or family-related elements without treating a trend as a substitute for element-specific evidence.
| Atomic number | 68 |
|---|---|
| Series | lanthanide |
| Atomic number | 69 |
|---|---|
| Series | lanthanide |
| Atomic number | 70 |
|---|---|
| Series | lanthanide |
Thulium 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 | 69 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 168.934 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Xe] 4f¹³ 6s² | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group Lanthanide · Period 6 · f-block | Periodic-table placement | Evaluated |
| Electronegativity | 1.25 | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ¹⁶⁹Tm | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Bright silvery lanthanide metal | Source-reviewed; see Sources below | Evaluated |
| Density | 9.32 g/cm³ | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Hexagonal close-packed (HCP) | Ordinary thulium metal is HCP. Tm-doped laser hosts and isotope source materials have different structures and are kept separate from the elemental lattice. | Measured |
| Classification | Lanthanide | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | Ordinary thulium metal is HCP. Tm-doped laser hosts and isotope source materials have different structures and are kept separate from the elemental lattice. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 1818 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 2223 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | At approximately standard pressure, thulium is treated as a solid below 1818 K, liquid between melting and approximately 2223 K, and gas above the boiling reference. The ordinary crystal label applies to the stated material reference; unmodeled solid allotropy is not fabricated. | 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, +2 | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Tm³⁺ | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Thulium is the penultimate lanthanide, with [Xe]4f¹³6s² ground state. Tm³⁺ dominates ordinary chemistry, while the nearly filled 4f shell produces useful near-infrared optical transitions. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ¹⁶⁹Tm | Natural isotope | Essentially all natural thulium is stable ¹⁶⁹Tm. | Evaluated |
| ¹⁷⁰Tm | Artificial radioisotope | Has isotope-specific x-ray-source applications. | Evaluated |
| Natural thulium | Single-isotope natural element | Natural thulium should not be described as broadly radioactive because an artificial isotope has a use. | Evaluated |
| Teaching nucleus | ¹⁶⁹Tm · 69 protons + 100 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic identity and reference values are source-reviewed. Material viewers are teaching representations, not crystallographic refinements. Search demand shapes headings and FAQs but never overrides measured/evaluated evidence or element-versus-compound distinctions. | Evidence summary for this guide | Reviewed |
| Structure evidence | Ordinary thulium metal is HCP. Tm-doped laser hosts and isotope source materials have different structures and are kept separate from the elemental lattice. | 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 Thulium a solid, liquid or gas? State at temperature
At approximately standard pressure, thulium is treated as a solid below 1818 K, liquid between melting and approximately 2223 K, and gas above the boiling reference. The ordinary crystal label applies to the stated material reference; unmodeled solid allotropy is not fabricated.
Where on Earth is Thulium found or produced?
Who discovered Thulium, and when?
Per Teodor Cleve isolated thulium oxide while examining erbium-rich rare-earth material in Uppsala.
Thulium was named after Thule, an ancient name associated with the far north.
High-purity thulium enabled isotope, laser and spectroscopy studies.
Tm remains one of the less abundant lanthanides and is used mainly in specialty optical/isotope contexts.
From source material to Thulium applications: high-level material path
Thulium is obtained from mineral or metallurgical feedstocks in which it is chemically associated with other elements rather than mined as abundant native metal.
Industrial separation and refining produce element-specific compounds or metal feedstock; this guide does not provide operational extraction recipes.
The refined material is converted into the particular alloy, compound, doped host or component required by the application.
Recycling and recovery depend on the host product, concentration and economics; application materials must not be confused with pure element.
What is thulium used for?
Near-IR lasers
Tm-doped fibers and crystals support useful near-2 μm laser systems.
Isotope sources
Artificial ¹⁷⁰Tm has been used in compact x-ray-source applications.
Spectroscopy
Tm ions provide characteristic optical transitions for research and sensing.
Specialty materials
Small Tm additions or compounds are used where specific optical/electronic behavior is needed.
Thulium isotopes and natural abundance
¹⁶⁹Tm
Natural isotopeEssentially all natural thulium is stable ¹⁶⁹Tm.
¹⁷⁰Tm
Artificial radioisotopeHas isotope-specific x-ray-source applications.
Natural thulium
Single-isotope natural elementNatural thulium should not be described as broadly radioactive because an artificial isotope has a use.
Five-question Thulium check
What is Thulium’s atomic number?
Which classification best fits Thulium?
What is the representative teaching isotope?
Which statement respects the material evidence?
Which rule should guide real-world uses?
Thulium 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 thulium?
Short answer: Thulium is chemical element 69, symbol Tm, a bright silvery lanthanide metal.
Atomic number 69 means every thulium nucleus contains 69 protons. In the periodic table, Thulium is classified here as a lanthanide in Period 6 and Group Lanthanide. Thulium is the penultimate lanthanide, with [Xe]4f¹³6s² ground state. Tm³⁺ dominates ordinary chemistry, while the nearly filled 4f shell produces useful near-infrared optical transitions.
Key point: Tm is element 69; its periodic position and electron structure explain the rest of the page.
What is thulium used for?
Short answer: It is used mainly in Tm-doped lasers, optical research and isotope-specific x-ray-source applications.
Near-IR lasers: Tm-doped fibers and crystals support useful near-2 μm laser systems. Isotope sources: Artificial ¹⁷⁰Tm has been used in compact x-ray-source applications. Thulium laser materials use Tm ions inside a host crystal or glass. The radioactive isotope ¹⁷⁰Tm has specialized x-ray-source history, but natural thulium is overwhelmingly stable ¹⁶⁹Tm; isotope-specific wording matters.
Key point: Always distinguish the pure element from the compound, alloy, isotope or device material that actually performs the application.
Where is thulium found?
Short answer: It occurs at low concentrations with other rare earths in minerals such as monazite and is separated during rare-earth processing.
Thulium is obtained from mineral or metallurgical feedstocks in which it is chemically associated with other elements rather than mined as abundant native metal. Rare-earth materials Thulium appears in specialized alloys and compounds where small additions can tune properties.
Key point: Natural occurrence, resources, production and recycling are different geography questions.
Who discovered thulium?
Short answer: Per Teodor Cleve isolated thulium in 1879.
In 1879, Per Teodor Cleve isolated thulium oxide while examining erbium-rich rare-earth material in Uppsala. Thulium was named after Thule, an ancient name associated with the far north.
Key point: Discovery credit follows the historical evidence and accepted attribution, not just the earliest claim.
Is thulium a metal?
Short answer: Yes. It is a lanthanide metal.
This guide classifies Thulium as a lanthanide. Its periodic position is Period 6, f-block, Group Lanthanide. Thulium is the penultimate lanthanide, with [Xe]4f¹³6s² ground state. Tm³⁺ dominates ordinary chemistry, while the nearly filled 4f shell produces useful near-infrared optical transitions.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
Is thulium radioactive?
Short answer: Natural thulium is essentially stable ¹⁶⁹Tm. Artificial radioisotopes such as ¹⁷⁰Tm are radioactive and have specialized uses.
¹⁶⁹Tm: Natural isotope: Essentially all natural thulium is stable ¹⁶⁹Tm. ¹⁷⁰Tm: Artificial radioisotope: Has isotope-specific x-ray-source applications.
Key point: Radioactivity is isotope-specific; do not apply one isotope’s nuclear behavior to every atom of the element.
How do you pronounce thulium?
Short answer: A common pronunciation is THOO-lee-um.
Pronunciation is a speaking aid; in chemical notation the element is identified unambiguously by the symbol Tm and atomic number 69. That distinction matters when element names are unfamiliar or similarly spelled.
Key point: Say the name as shown, but use Tm and atomic number 69 for unambiguous chemical identity.
How many electrons does thulium have?
Short answer: A neutral thulium atom has 69 electrons with ground-state configuration [Xe] 4f¹³ 6s².
A neutral atom has the same number of electrons as protons, so neutral Thulium has 69 electrons. Its ground-state reference configuration is [Xe] 4f¹³ 6s²; ions have different electron counts because electrons have been removed or added.
Key point: Electron count changes in ions; proton count does not.
Scientific sources for Thulium
- Royal Society of Chemistry - Thulium
- NIST - Atomic Weights and Isotopic Compositions
- IUPAC - Periodic Table of Elements
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