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1H1.008
Reactive Nonmetalsgas at STPS-block

Hydrogen

Group: 1Period: 1Standard Atomic Weight: 1.008 u

Why is Hydrogen in this position?

Understanding the scientific rationale behind Hydrogen's position in the periodic table:

Group Assignment
Group 1

Placed in Group 1 because its neutral atom possesses 1 valence electron in the outermost shell (1s¹).

Period Assignment
Period 1

Occupies Period 1 because its single electron fills the first principal energy level (n=1).

Orbital Block
S-block

Belongs to the s-block because the differentiating valence electron enters an s-orbital.

Chemical Category
Reactive Nonmetals

Classified as a reactive nonmetal due to its high ionization energy, gas phase at standard conditions, and ability to form covalent bonds.

Atomic Structure & Bohr Shell Model

Shell Distribution: [1]

Bohr Atomic Shell Model(1)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

1 Protons (p⁺)0 Neutrons (n⁰)
KShell K: Electron 1 of 1HZ = 1

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):1 / 2 electrons (50%)
Aufbau Electron Configuration
1s¹

Neutral ground state configuration. Valence electrons: 1.

Atomic & Quantum Properties

Electronegativity (Pauling)2.2 Pauling
1st Ionization Energy1312 kJ/mol
Electron Affinity-72.8 kJ/mol
Atomic Radius (empirical)53 pm
Common Oxidation States+1, -1
Crystal StructureHexagonal

Physical & Thermal Properties

Density at STP0.0000899 g/cm³
Melting Point-259.16 °C (13.99 K)
Boiling Point-252.87 °C (20.28 K)
Magnetic OrderingDiamagnetic
Discovery Year1766
Discovered ByHenry Cavendish

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Rocket propulsion and hydrogen fuel cells
  • Industrial ammonia synthesis via Haber process
  • Hydrogenation of vegetable oils into fats
  • Petroleum refining, hydrocracking & desulfurization
Occurrence in Nature

Found ubiquitously in water (H₂O), hydrocarbons, and cosmic interstellar gas clouds; rare as free H₂ gas in Earth's atmosphere.

Etymology & Name Origin

From Greek 'hydro' and 'genes', meaning water-forming

Important Chemical Compounds
H₂O (Water)
NH₃ (Ammonia)
HCl (Hydrochloric acid)
H₂SO₄ (Sulfuric acid)
CH₄ (Methane)
Interesting Chemical Facts
  • Hydrogen is the only element without neutrons in its most common isotope (Protium, ¹H).
  • Under extreme pressures exceeding 400 GPa, hydrogen transitions into a metallic, superconducting fluid.
  • Liquid hydrogen is one of the coldest cryogenic liquids, boiling at just 20.28 K (-252.87 °C).
Safety & Handling Note

Extremely flammable gas; forms explosive mixtures with air at concentrations between 4% and 75%.

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