Hydrogen vs Selenium

Side-by-side comparison of Hydrogen (H, element 1) and Selenium (Se, element 34) by atomic structure and physical properties.

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PropertyH Hydrogen Se Selenium
Atomic number134
SymbolHSe
NameHydrogenSelenium
Categorynonmetalnonmetal
Standard Atomic Weight1.007975 u78.971 u
Period14
Group116
Blocksp
Phase at STPGasSolid
Electron configuration1s1[Ar]4s23d104p4
Oxidation states[-1, 1][-2, -1, 0, 1, 2, 3, 4, 5, 6]
Electronegativity (Pauling)2.22.55
Electron affinity0.75419 eV2.0206 eV
Density0.08988 kg/m³4809 kg/m³
Melting point-259.193 °C220.5 °C
Boiling point-252.781 °C684.85 °C
Discovery year17661817

Key Differences

PropertyH HydrogenSe Selenium
Standard Atomic Weight1.007975 u ↓ lower78.971 u ↑ higher
Density0.08988 kg/m³ ↓ lower4809 kg/m³ ↑ higher
Melting point-259.193 °C ↓ lower220.5 °C ↑ higher
Boiling point-252.781 °C ↓ lower684.85 °C ↑ higher
Electronegativity (Pauling)2.2 ↓ lower2.55 ↑ higher
Electron affinity0.75419 eV ↓ lower2.0206 eV ↑ higher
Period1 4
Group1 16
Blocks p
Phase at STPGas Solid
Electron configuration1s1 [Ar]4s23d104p4
Discovery year1766 1817