Hydrogen vs Helium
Side-by-side comparison of Hydrogen (H, element 1) and Helium (He, element 2) by atomic structure and physical properties.
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| Atomic number | 1 | 2 |
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| Symbol | H | He |
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| Name | Hydrogen | Helium |
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| Category | nonmetal | noble-gas |
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| Standard Atomic Weight | 1.007975 u | 4.002602 u |
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| Period | 1 | 1 |
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| Group | 1 | 18 |
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| Block | s | s |
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| Phase at STP | Gas | Gas |
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| Electron configuration | 1s1 | 1s2 |
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| Oxidation states | [-1, 1] | [0] |
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| Electronegativity (Pauling) | 2.2 | N/A |
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| Electron affinity | 0.75419 eV | -0.5 eV |
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| Density | 0.08988 kg/m³ | 0.1785 kg/m³ |
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| Melting point | -259.193 °C | -272.2 °C |
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| Boiling point | -252.781 °C | -268.93 °C |
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| Discovery year | 1766 | 1868 |
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Key Differences
| H Hydrogen | He Helium |
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| Standard Atomic Weight | 1.007975 u ↓ lower | 4.002602 u ↑ higher |
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| Density | 0.08988 kg/m³ ↓ lower | 0.1785 kg/m³ ↑ higher |
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| Melting point | -259.193 °C ↑ higher | -272.2 °C ↓ lower |
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| Boiling point | -252.781 °C ↑ higher | -268.93 °C ↓ lower |
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| Electron affinity | 0.75419 eV ↑ higher | -0.5 eV ↓ lower |
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| Group | 1 | 18 |
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| Category | nonmetal | noble-gas |
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| Electron configuration | 1s1 | 1s2 |
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| Discovery year | 1766 | 1868 |
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