Element 1 · Gas at room temperature
Hydrogen
Looks like: colorless gas.
Hydrogen is atom number 1 — every Hydrogen atom has exactly 1 protons in its center, and that number is what makes it Hydrogen and nothing else. Its symbol is H. At room temperature it is a gas.
Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.
Summary from the source dataset, derived from Wikipedia (CC BY-SA 3.0) · original article
Hydrogen sits in period 1, group 1 of the s-block. Its 1 electrons fill shells of 1 — written as 1s1. Its electronegativity is 2.2 on the Pauling scale, and pulling the first electron off takes 1312 kJ/mol. The outermost shell holds 1 electron — the ones that do all the chemistry.
Full configuration: 1s1
Ionization energies (kJ/mol): 1312
Electron affinity: 72.769 kJ/mol · Electronegativity (Pauling):
2.2
Density: 0.08988
g/L · melts 13.99 K · boils 20.271 K
Values exactly as published — see where the data comes from.
Atomic mass
1.008u
Density
0.08988g/L
Melts
13.99 K
Boils
20.271 K
The units on this page — explained by Unitii
Hydrogen's family
Elements in the same column share their outer-electron count, so they behave alike.
What it becomes
Everyday compounds in our curated set that contain Hydrogen — the upward direction of the map: atom → molecule → stuff you know.
Source
Discovered by Henry Cavendish. Named by Antoine Lavoisier.
Periodic-Table-JSON (Bowserinator and contributors); element summaries derived from Wikipedia · CC BY-SA 3.0 · snapshot retrieved 2026-08-21