Hydrogen is the lightest and most basic chemical element in the entire universe. Its symbol on the periodic table is H, and its atomic number is 1 — meaning each hydrogen atom has just one proton and one electron. This simplicity makes it unique among all elements.
A closer look at hydrogen, the smallest atom with the biggest impact. This is the “solar-system” model for hydrogen.
In nature, hydrogen atoms rarely exist on their own. Instead, two hydrogen atoms link together to form hydrogen gas, written as H₂. This gas is:
- colorless (no visible color)
- odorless (no smell)
- less dense than air (lighter than air — so it rises quickly and disperses).
The Most Abundant Element in the Universe
Although it’s rare in Earth’s atmosphere, hydrogen is the most abundant element in the universe. This single element makes up about 75% of all matter in stars and space. Most of this hydrogen was created in the first few minutes after the Big Bang event, approximately 13.8 billion years ago.1Wikimedia Foundation. (2026, March 6). Big Bang nucleosynthesis. Wikipedia. https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis.2Wikimedia Foundation. (2026, March 2). Big Bang. Wikipedia. https://en.wikipedia.org/wiki/Big_Bang.
On Earth, hydrogen is usually found combined with other elements, for example, in water (H₂O) or in fossil fuels like methane (CH₄). Hydrogen almost never exists as pure H₂ unless humans make it or the gas escapes from rocks and soils.3U.S. Energy Information Administration. (n.d.). Hydrogen. Hydrogen (Energy Kids page).
Why does this matter for energy?
Because hydrogen can store energy that we can release later. As we’ll see, that makes it exciting for clean energy — even if we have to make it first.