| General |
|---|
| Name | Helium | | Symbol | He | | Number | 2 | | Chemical series | Noble gases | | Group / Period | 18 / 1 | | Block | s-block | | CAS registry number | 7440-59-7 |
| Physical properties |
|---|
| State | gas | | Density | 0.1786 g/L | | Melting point | 0.95 K (−272.2 °C, −458.0 °F) | | Boiling point | 4.22 K (−268.93 °C, −452.07 °F) | | Critical point | 5.19 K, 0.227 MPa |
| Atomic properties |
|---|
| Atomic Weight | 4.002602 g/mol | | Crystal structure | cubic body centered | | Electronegativity | | | Atomic radius | 128 pm | | Atomic radius (calculated) | 31 pm | | Electron configuration | 1s2 | | Electrons per shell | 2 | | Number of protons | 2 | | Number of neutrons | 2 |
|
Lithium