2
He
Helium
4.0026022
Helium
NOBLE GAS
Bohr Model: Electrons arranged in energy shells around the nucleus.
Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table. Its boiling and melting points are the lowest among all the elements.
Quick Facts
Atomic Number 2
Period 1
Group 18
Phase Gas
Appearance colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field
About Noble Gass
Noble gases are colorless, odorless, and extremely unreactive (inert) due to having full valence electron shells.
History
Discovered By Pierre Janssen
Named By Unknown
Physical Properties
Atomic Mass 4.0026022
Density 0.1786 g/L
Molar Heat N/A J/(mol·K)
Phase Transition (Melting & Boiling Points)
Helium melts at 0.95 K and boils at 4.222 K.
Atomic Properties
Electron Config 1s2
Electronegativity N/A
Electron Affinity -48 kJ/mol
Ionization Energy 2372.3 kJ/mol
Orbital Filling Diagram
This diagram visualizes electron configuration according to the Aufbau principle and Hund's rule.
Boxes represent orbitals (s, p, d, f), while arrows indicate electrons with spin up or down.
Electrons fill lower energy levels first and occupy orbitals singly before pairing.
Emission Spectrum
Photograph
External Resources
Study Guide
Atomic Number
The number of protons in the nucleus, which defines the element.
Atomic Mass
The average mass of an atom, including protons and neutrons.
Electronegativity
A measure of how strongly an atom attracts electrons in a bond.
Ionization Energy
The energy required to remove an electron from an atom.
Electron Config
The arrangement of electrons in the atom's energy shells.