Atomic / phase data
Reference atomic and gray-selenium physical values are evaluated.
Gray selenium helix
Trigonal gray selenium is built from helical chains; the viewer is a motif-level teaching model.
Allotrope story
Red and gray allotropes are distinguished without inventing one universal solid-solid transition temperature.
Supply chain
Commercial selenium is commonly recovered as a copper-refining by-product; geography is supply-chain context.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Selenium (Se)
Selenium is element 34, a Group 16 element whose gray and red allotropes connect bonding, structure and light-sensitive electrical behavior. Most commercial selenium is recovered as a by-product of copper refining rather than from a dedicated selenium mine.
Selenium atomic number, mass, electron configuration and key properties
Selenium: quick answers
How many protons, neutrons and electrons does selenium have?
Selenium’s atomic number is 34, so every selenium atom has 34 protons, and a neutral atom also has 34 electrons. Its most common natural isotope, selenium-80, has 46 neutrons (other isotopes have different neutron counts).
What is the symbol for selenium?
The chemical symbol for selenium is Se.
Is selenium a solid, liquid or gas at room temperature?
Selenium is a solid at room temperature (about 25 °C).
What family (group) is selenium in?
Selenium is a nonmetal, in group 16, period 4 of the periodic table.
How many valence electrons does selenium have?
Selenium has 6 valence electrons, the electrons in its outer shell, which matches its position in group 16.
What is the electron configuration of selenium?
The ground-state electron configuration of selenium is [Ar] 3d¹⁰ 4s² 4p⁴.
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.
34 protons define selenium.
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.
Selenium in its period and family
Selenium sits in Group 16, Period 4, below sulfur and above tellurium. Its six valence electrons support −2 chemistry as well as positive oxidation states such as +4 and +6.
Selenium Visual Lab
Compare Se with Se²⁻, inspect a ⁸⁰Se teaching nucleus, rotate a gray-selenium helical motif, explore 4p orbitals, then connect allotropy to photoconductivity, glassmaking, copper-refinery recovery and trace-element biology.
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.
Selenium in one minute
Atomic number 34 means 34 protons.
Neutral selenium has [Ar] 3d¹⁰ 4s² 4p⁴.
Gray selenium uses helical chains and is the most stable allotrope under ordinary conditions.
Gray selenium is photoconductive: its electrical response changes with illumination.
Selenium is an essential trace nutrient in small amounts, but excess exposure can be harmful.
Shell rings organize electron counts. They are not electron trajectories or orbital shapes.
2 · 8 · 18 · 6 electrons
The 4s and 4p probability clouds are hydrogen-like teaching distributions. Selecting pₓ/pᵧ/p𝓏 changes orientation; the plots are not crystalline band structures.
The material view emphasizes the repeating helical-chain motif of stable gray/trigonal selenium. Red allotropes have different molecular/polymeric structures and are handled in Signature Science.. 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 4s and 4p probability clouds are hydrogen-like teaching distributions. Selecting pₓ/pᵧ/p𝓏 changes orientation; the plots are not crystalline band structures.
Where do I meet selenium?
Clickable learning cards connect the element to materials, environment, technology, biology or research - depending on what the evidence actually supports.
Glass
Selenium compounds can decolorize glass or impart red/bronze tones.
Red allotropes → gray helices → photoconductivity
Selenium’s structure changes its macroscopic behavior, making it a strong example of why “same element” does not mean “same material properties.”
Red selenium forms
Red selenium can occur in molecular/polymeric allotrope forms rather than the stable gray helical structure.
Sulfur, selenium and tellurium
Group 16 shares six valence electrons while structures and physical character change down the column.
| Valence | 3s²3p⁴ |
|---|---|
| Ordinary motif | S₈ molecules |
| Valence | 4s²4p⁴ |
|---|---|
| Stable motif | helical chains |
| Valence | 5s²5p⁴ |
|---|---|
| Character | metalloid-like |
Selenium 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 | 34 | Source-reviewed; see Sources below | Evaluated |
| Relative atomic mass | 78.971 | Source-reviewed; see Sources below | Evaluated |
| Ground-state electron configuration | [Ar] 3d¹⁰ 4s² 4p⁴ | Source-reviewed; see Sources below | Evaluated |
| Group / period / block | Group 16 · Period 4 · p-block | Periodic-table placement | Evaluated |
| Electronegativity | 2.55 | Source-reviewed; see Sources below | Evaluated |
| Reference isotope | ⁸⁰Se | Source-reviewed; see Sources below | Evaluated |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| State context | Solid at 20 °C · gray/red allotropes | Source-reviewed; see Sources below | Evaluated |
| Density | 4.809 g/cm³ (gray Se) | Source-reviewed; see Sources below | Evaluated |
| Material / molecular structure | Gray selenium · trigonal helical chains | The material view emphasizes the repeating helical-chain motif of stable gray/trigonal selenium. Red allotropes have different molecular/polymeric structures and are handled in Signature Science. | Measured |
| Classification | Chalcogen / nonmetal-metalloid border | Periodic-table / chemistry classification | Evaluated |
| Structure-model scope | The material view emphasizes the repeating helical-chain motif of stable gray/trigonal selenium. Red allotropes have different molecular/polymeric structures and are handled in Signature Science. | Teaching visualization; exact crystallographic coordinates are not implied unless stated. | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Melting / transition reference | 494 K | Source-reviewed; see Sources below | Evaluated |
| Boiling / gas reference | 958 K | Source-reviewed; see Sources below | Evaluated |
| Phase-path context | A bulk teaching path uses gray selenium as the ordinary solid reference, melting near 494 K and boiling near 958 K. Solid-allotrope transformations are complex and are not reduced to a fabricated single transition temperature. | 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 | −2, +4, +6 | Source-reviewed; see Sources below | Evaluated |
| Ion / common ion context | Se²⁻ | Source-reviewed; see Sources below | Evaluated |
| Periodic chemistry context | Selenium sits in Group 16, Period 4, below sulfur and above tellurium. Its six valence electrons support −2 chemistry as well as positive oxidation states such as +4 and +6. | Element-specific interpretation | Reviewed |
| Chemistry caution | Elemental form, ions and compounds are distinct chemical objects. | Interpretive teaching rule | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| ⁸⁰Se | Stable · most abundant natural isotope | Reference teaching nucleus with 34 protons and 46 neutrons. | Evaluated |
| ⁷⁸Se | Stable natural isotope | One of several stable selenium isotopes. | Evaluated |
| ⁸²Se | Very long-lived double-beta isotope | Important in nuclear/particle-physics research contexts. | Evaluated |
| Teaching nucleus | ⁸⁰Se · 34 protons + 46 neutrons | Reference isotope used in the nucleus model | Reviewed |
| Property | Value | Context / provenance | Evidence |
|---|---|---|---|
| Page evidence note | Atomic and ordinary physical values are evaluated. The gray-selenium helical structure is a teaching motif, not a full coordinate reconstruction. Supply-chain statements emphasize by-product recovery rather than invented “selenium mine” pins. | Evidence summary for this guide | Reviewed |
| Structure evidence | The material view emphasizes the repeating helical-chain motif of stable gray/trigonal selenium. Red allotropes have different molecular/polymeric structures and are handled in Signature Science. | 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 Selenium a solid, liquid or gas? State at temperature
A bulk teaching path uses gray selenium as the ordinary solid reference, melting near 494 K and boiling near 958 K. Solid-allotrope transformations are complex and are not reduced to a fabricated single transition temperature.
Where on Earth is Selenium found or produced?
Who discovered Selenium, and when?
Jöns Jacob Berzelius identified selenium while investigating residues from sulfuric-acid production in Sweden.
Selenium’s light-sensitive electrical behavior was discovered and became important in early photoelectric technologies.
Glass, pigments, rectifiers and imaging uses expanded, while copper refining became a major supply route.
Selenium spans materials, metallurgy, glassmaking, electronics and trace-element biology.
From copper-refinery by-product to selenium materials: a high-level path
Selenium occurs dispersed in sulfide ores and is rarely produced from a dedicated selenium ore body.
During electrolytic copper refining, selenium can concentrate in anode slimes.
Industrial recovery converts these by-product streams into selenium and selenium compounds in controlled facilities.
Refined selenium then enters glass, pigment, metallurgical, electronic and chemical applications.
What is selenium used for?
Glass & pigments
Selenium chemistry controls glass color and appears in red/ceramic pigments.
Electronics & sensing
Photoconductive and photovoltaic responses made selenium important in photocells and historical imaging/rectifier technologies.
Metallurgy
Small selenium additions can modify machinability and other properties of selected alloys.
Biological chemistry
Selenium is part of selenoproteins at trace levels, distinct from bulk elemental selenium applications.
Selenium isotopes and natural abundance
⁸⁰Se
Stable · most abundant natural isotopeReference teaching nucleus with 34 protons and 46 neutrons.
⁷⁸Se
Stable natural isotopeOne of several stable selenium isotopes.
⁸²Se
Very long-lived double-beta isotopeImportant in nuclear/particle-physics research contexts.
Five-question Selenium check
What is selenium’s atomic number?
How many valence electrons does selenium have?
Which allotrope is the stable ordinary teaching reference?
What electrical behavior is selenium known for?
A major commercial selenium source is…
Selenium 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 selenium’s atomic number?
Short answer: 34.
Atomic number is defined by proton count, so 34 protons are what make an atom selenium. A neutral selenium atom also has 34 electrons, while isotopes can have different neutron counts without changing the element.
Key point: Atomic number = proton count.
Is selenium a metal?
Short answer: It is commonly described as a nonmetal with semiconducting/metalloid-like physical behavior depending on allotrope; simple labels do not capture all of its materials science.
This guide classifies Selenium as a chalcogen / nonmetal-metalloid border. Its periodic position is Period 4, p-block, Group 16. Selenium sits in Group 16, Period 4, below sulfur and above tellurium. Its six valence electrons support −2 chemistry as well as positive oxidation states such as +4 and +6.
Key point: Periodic-table classification describes recurring atomic/chemical behavior; it does not make every element in a column physically identical.
How many valence electrons does selenium have?
Short answer: Six, from 4s²4p⁴.
The neutral-atom ground-state reference used on this page is [Ar] 3d¹⁰ 4s² 4p⁴. This is an isolated-atom reference: bonding and ion formation can change which outer electrons are present or chemically active. The listed common oxidation-state context is −2, +4, +6, which helps connect the atomic configuration to ordinary chemistry without treating electron counting as a single universal rule.
Key point: Electron configuration is a ground-state atomic reference, not a literal picture of every compound.
Why is selenium used in light-sensitive devices?
Short answer: Gray selenium is photoconductive: illumination changes its electrical conductivity.
Selenium is element 34, a Group 16 element whose gray and red allotropes connect bonding, structure and light-sensitive electrical behavior. Most commercial selenium is recovered as a by-product of copper refining rather than from a dedicated selenium mine. Gray selenium is photoconductive: its electrical response changes with illumination.
Key point: The mechanism matters: connect the observed behavior to electron structure, bonding, phase or the specific material form rather than memorizing the result alone.
Where does commercial selenium come from?
Short answer: Much is recovered as a by-product from anode slimes in electrolytic copper refining.
Copper-refinery by-product Commercial selenium is commonly recovered from anode slimes generated during electrolytic copper refining. Selenium is element 34, a Group 16 element whose gray and red allotropes connect bonding, structure and light-sensitive electrical behavior. Most commercial selenium is recovered as a by-product of copper refining rather than from a dedicated selenium mine.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Is selenium good or bad for health?
Short answer: It is an essential trace element at appropriate intake, but excess exposure can be harmful; nutritional advice belongs with qualified health sources.
Selenium is an essential trace nutrient in small amounts, but excess exposure can be harmful. Selenium is biologically essential in trace amounts but can be toxic in excess. This page is chemistry education, not nutritional or medical advice.
Key point: Use the direct answer together with the material, isotope and evidence context shown elsewhere on the page.
Scientific sources for Selenium
- Royal Society of Chemistry - Selenium
- NIST - Atomic Data for Selenium
- USGS - Selenium statistics and information
Found an error, something unclear, or a missing topic?
Tell us what you noticed. Feedback goes to a private review queue and is never published automatically.