Element identity
Atomic number, symbol, relative atomic mass display and periodic position are established reference data.
Atomic / electronic model
Ground-state electron configuration and atomic reference values are compiled/evaluated data; orbital graphics are teaching probability models, not photographs.
Material / molecular structure
The displayed ordinary structure is based on established material or molecular science; simplified viewers are labelled as teaching schematics where exact crystallographic coordinates are not rendered.
Temperature / phase path
Transition values are reference/evaluated values for the stated teaching path; pressure, purity and allotropy can matter.
Geography
Real pins use reviewed place/dataset context. Conceptual layers are used when country pins would imply false occurrence, unsafe inventory or an incomplete global distribution.
The lens describes evidence status, not confidence theatre. “Unknown” is kept unknown, and teaching schematics are not presented as direct measurements.
Hydrogen (H)
Explore the lightest element as a one-electron atom, the H₂ molecule, three famous isotopes, an unusual Group 1 exception, a cryogenic phase system and a global Earth-and-universe reservoir story.
Hydrogen atomic number, mass, protons, electrons and isotopes
Hydrogen: quick answers
How many protons, neutrons and electrons does hydrogen have?
Hydrogen’s atomic number is 1, so every hydrogen atom has 1 proton, and a neutral atom also has 1 electron. The most common isotope, hydrogen-1 (protium), has no neutrons; deuterium has one and tritium has two.
What is the symbol for hydrogen?
The chemical symbol for hydrogen is H.
Is hydrogen a solid, liquid or gas at room temperature?
Hydrogen is a gas at room temperature (about 25 °C).
What family (group) is hydrogen in?
Hydrogen is a nonmetal, in group 1, period 1 of the periodic table.
How many valence electrons does hydrogen have?
Hydrogen has 1 valence electron, the single electron in its outer shell, which matches its position in group 1.
What is the electron configuration of hydrogen?
The ground-state electron configuration of hydrogen is 1s¹.
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.
One proton defines hydrogen and a neutral atom contains one electron.
The single first-shell electron explains why hydrogen can share, lose or gain electron density.
The 1s¹ pattern places hydrogen above Group 1 while its chemistry remains distinct from alkali metals.
Changing neutron count creates hydrogen isotopes without changing element identity.
Hydrogen is above Group 1 — but it is not an ordinary alkali metal
The 1s¹ configuration gives hydrogen the one-outer-electron pattern associated with Group 1, but its small size, high ionization energy and molecular nonmetal chemistry make it exceptional.
Hydrogen Visual Lab
Decode the hydrogen tile, rotate a protium teaching model, inspect the 1s probability cloud, compare hydrogen isotopes, then connect H chemistry to water, stars, fuels and industry.
Seven facts packed into one square
Hydrogen in one minute
One proton defines hydrogen. Change the proton number and the element changes.
1s¹ is exceptional. Hydrogen shares the Group 1 electron-count pattern but not ordinary alkali-metal behavior.
H₂ is the ordinary elemental form. Two H atoms share electrons in a diatomic molecule.
Three famous isotopes. Protium and deuterium are stable; tritium is radioactive.
Earth hydrogen is mostly bound. Water and compounds are far more important natural reservoirs than free H₂.
1 electron in the first shell
The single electron can be shared in covalent bonds, removed in ionization bookkeeping, or joined by another electron in hydride chemistry. The same 1s¹ starting point does not force one single bonding mode.
Under ordinary conditions elemental hydrogen is primarily diatomic H₂: two hydrogen atoms share electron density in a molecule. It is not a room-temperature metallic crystal lattice.
This schematic shows molecular connectivity; it is not a literal electron trajectory or electron-density calculation.1s¹
A one-electron atom is the simplest atomic system. Its hydrogenic orbitals provide the starting language used to understand more complicated many-electron atoms.
Protium · ¹H
Protium contains one proton and no neutron. It is stable and accounts for about 99.9885% in the NIST terrestrial natural-isotope composition table.
Where do I meet hydrogen?
Clickable learning cards connect one element to water, stars, ammonia, fuel cells, organic matter and isotope science.
Most familiar terrestrial hydrogen is chemically bound
Hydrogen is built into H₂O throughout oceans, ice, groundwater and living systems. Free H₂ gas is not a good map of total natural hydrogen occurrence.
Protium, deuterium and tritium: same element, different nuclei
All hydrogen isotopes have one proton. Changing neutron number changes mass number and nuclear stability without changing element identity.
From one 1s electron to the H₂ molecule
Hydrogen’s one electron can participate in covalent bonding, ionization and hydride chemistry. Use the controls to separate these ideas rather than treating every hydrogen-containing substance as the same chemical form.
Two nuclei share a pair of electrons
Combining two 1s atomic orbitals produces molecular orbitals. Two electrons occupy the lower-energy bonding orbital in ordinary H₂.
Molecular model, not a classical orbitHydrogen properties: atomic, molecular, chemical and isotope context
Hydrogen data must distinguish atomic H from molecular H₂ and separate ordinary chemical properties from isotope-specific nuclear behavior.
| Atomic number | 1 | One proton defines hydrogen. |
|---|---|---|
| Relative atomic mass | 1.008 | Natural isotope-weighted reference display. |
| Electron configuration | 1s¹ | Ground-state neutral atom. |
| Electronegativity | 2.20 | Pauling scale. |
| Non-bonded atomic radius | 1.10 Å | RSC reference; radius depends on definition. |
| 1st ionization energy | 1312.05 kJ/mol | Gaseous ground-state atom. |
| Ordinary elemental form | H₂ | Diatomic molecular gas near room conditions. |
|---|---|---|
| Melting point | 13.99 K | Approximately standard-pressure reference. |
| Boiling point | 20.271 K | Approximately standard-pressure reference. |
| H–H bond enthalpy | 435.9 kJ/mol | RSC reference value. |
| Common oxidation state | +1 | Common bookkeeping state in many compounds. |
|---|---|---|
| Hydrides | −1 possible | Formal state in ionic/metal hydride descriptions. |
| Representative compounds | H₂O, NH₃, CH₄ | Hydrogen is widely chemically bound. |
| Electron affinity | 72.769 kJ/mol | Reference for gaseous H + e⁻ → H⁻. |
| ¹H | ≈99.9885% | Stable · 1 p · 0 n. |
|---|---|---|
| ²H | ≈0.0115% | Stable · 1 p · 1 n. |
| ³H | radioactive | No standard natural abundance in the NIST composition table. |
Hydrogen state at temperature: solid → liquid → gas
Molecular hydrogen has a normal cryogenic liquid interval. This view therefore follows the scientifically appropriate solid–liquid–gas path on a compact low-temperature scale.
The entire solid–liquid–gas sequence shown here occurs far below room temperature. At ordinary room conditions elemental hydrogen is a gas.
At 20 K molecular hydrogen lies in the narrow liquid interval on this approximate-pressure path.Interactive hydrogen reservoirs: where terrestrial hydrogen is stored
Natural hydrogen is mostly chemically bound. Click a reservoir to see why a simple country-dot occurrence map would be misleading.
Hydrogen geography: global reservoirs, not “hydrogen countries”
The scientifically honest geography layers are global water, compounds and trace free-gas context rather than invented natural-deposit rankings.
Hydrogen history: from “inflammable air” to isotope science
Henry Cavendish
Characterized “inflammable air” as a distinct gas.
Antoine Lavoisier
Named hydrogen from roots associated with “water-former.”
Deuterium
Harold Urey and colleagues detected the heavy stable isotope.
Industrial feedstock
Hydrogen became central to ammonia manufacture, refining and chemical processing.
Energy research
Hydrogen production, storage and electrochemical use remain active engineering fields.
How industrial hydrogen is produced
Hydrogen is an energy carrier/feedstock rather than a freely mined metal. Commercial routes include hydrocarbon conversion and water electrolysis; climate impact depends strongly on feedstock, energy source and process emissions.
Choose a feedstock
Water, natural gas and other hydrogen-containing materials can serve as sources.
Supply energy
Chemical conversion or electricity is required to separate hydrogen from compounds.
Separate + purify
The hydrogen-rich stream is processed to the purity needed for its application.
Compress, liquefy or use
Storage and transport are engineering challenges because hydrogen is a very light molecule.
Where hydrogen is used
Ammonia
A major industrial feedstock for ammonia manufacture and fertilizer chemistry.
Refining + synthesis
Used in hydroprocessing and many chemical-manufacturing routes.
Fuel cells
Can be oxidized electrochemically to generate electricity with water at the point of use.
Hydrogenation
Hydrogen addition is an important reaction family in industrial and laboratory chemistry.
Stars
Hydrogen nuclei are the starting fuel for fusion chains in main-sequence stars.
Isotope tracing
Deuterium and tritium support scientific tracing and research applications under appropriate controls.
Hydrogen-1, hydrogen-2 and hydrogen-3
Five-question Hydrogen check
What defines every hydrogen atom?
Which isotope has one neutron?
What is the ordinary elemental molecular form?
Why is hydrogen not simply an alkali metal?
At room temperature, elemental H₂ is mainly what state?
Hydrogen questions: quick answer first, then the mechanism
Open a question for the fast fact and the deeper chemistry behind it.
Why is hydrogen in Group 1 if it is not an alkali metal?
Short answer: Hydrogen has a 1s¹ outer configuration, matching the one-electron pattern at the top of Group 1, but its molecular nonmetal chemistry is distinctive.
Group placement captures a useful electron-configuration relationship. It does not mean every property must match lithium, sodium and potassium. Hydrogen can share electrons covalently, appear as H⁺ in chemical bookkeeping and form hydrides with formal H⁻.
Hydrogen isotopes: what is the difference between protium, deuterium and tritium?
Short answer: All three nuclei contain one proton; protium has 0 neutrons, deuterium 1 neutron and tritium 2 neutrons. Protium and deuterium are stable, while tritium is radioactive.
The proton count stays at Z = 1, so all are hydrogen and neutral atoms have the same basic one-electron electronic structure. Changing neutron number changes nuclear mass and stability. The larger relative mass differences also create measurable isotope effects in vibrational frequencies, diffusion and reaction rates, so isotopes are chemically similar but not perfectly identical in every physical or kinetic property.
Tritium radioactivity is a nuclear property. It does not mean ordinary protium or deuterium chemistry is “radioactive chemistry.”
Key point: Same proton number = same element; different neutron number = different isotope, mass and potentially nuclear stability.
Why is hydrogen usually written H₂?
Short answer: Under ordinary conditions elemental hydrogen is a diatomic molecular gas.
Two hydrogen atoms can combine their 1s-derived states into molecular orbitals, with two electrons occupying the bonding state in ordinary H₂.
Where is hydrogen found naturally on Earth?
Short answer: Mostly in compounds, especially water and organic matter.
Hydrogen is widespread in H₂O, hydrocarbons, biomolecules and minerals containing hydroxyl groups or bound water. Free H₂ is not a useful proxy for total terrestrial hydrogen.
Why is liquid hydrogen so cold?
Short answer: H₂ molecules have weak intermolecular attractions and a very low boiling point.
At approximately standard pressure hydrogen boils near 20.271 K, so maintaining the liquid requires cryogenic temperatures.
Scientific sources for Hydrogen
Atomic, isotope and phase values are tied to authoritative reference sources. The Earth section intentionally distinguishes broad natural reservoirs from industrial production.
Questions to ask next about Hydrogen
A good element lesson should lead to the next useful question, not end after a list of facts.
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