What Is Hydrogen?
QUICK ANSWER
Hydrogen is the lightest chemical element, with atomic number 1 and the symbol H. It is a colorless, odorless gas at room temperature and the most abundant element in the universe, making up about 75% of all normal matter. Hydrogen fuels stars and is finding increasing use as a clean energy carrier.
Hydrogen sits at position 1 on the periodic table for a reason: it is the simplest, lightest, and most common element in the cosmos. Stars burn hydrogen through nuclear fusion. Water is two parts hydrogen, one part oxygen. And as the world moves toward cleaner energy, hydrogen is increasingly seen as a fuel of the future for vehicles, industry, and electricity generation.
Where is hydrogen on the periodic table?
Hydrogen has atomic number 1, the symbol H, and sits at the top of group 1, though its properties are unique enough that it does not perfectly fit any group. Each atom has one proton and one electron, with an atomic mass of about 1.008. Hydrogen has three isotopes: protium (no neutrons, 99.98% of natural hydrogen), deuterium (one neutron, 0.02%), and tritium (two neutrons, radioactive and made artificially). Hydrogen normally exists as a diatomic molecule (H₂) at standard conditions in the air.
What are the properties of hydrogen?
Hydrogen is a colorless, odorless, tasteless gas that is about 14 times less dense than air, which is why hydrogen balloons rise so quickly. It liquefies at -253°C and freezes at -259°C. It is highly flammable, burning with a nearly invisible pale blue flame, which is why hydrogen explosions can be dangerous to detect. Hydrogen reacts readily with most non-metals and many metals, forming compounds from water (H₂O) to ammonia (NH₃) to hydrocarbons. It is the most chemically active element after fluorine and forms more compounds than any other element.
What is hydrogen used for?
Hydrogen has wide industrial uses. About 55% goes into making ammonia for fertilizer through the Haber-Bosch process. Refineries use hydrogen to remove sulfur from gasoline and diesel and to crack heavy oils into lighter fuels. Hydrogen rocket fuel powered the Space Shuttle main engines and continues to power modern rockets. Increasingly, hydrogen fuel cells generate electricity for vehicles and stationary power, producing only water as exhaust. Hydrogen is also used in food production to hydrogenate vegetable oils into margarine and similar products.
Why is hydrogen abundant in the universe?
Hydrogen formed within the first few minutes after the Big Bang, when conditions cooled enough for protons and electrons to combine. Because it is the simplest element, it requires the least energy to form, and the universe has been hydrogen-rich ever since. Stars are mostly hydrogen, fusing it into helium and releasing energy in the process. Even today, about 75% of all visible matter in the universe is hydrogen. On Earth, hydrogen is rare in pure form because it is so light it tends to escape into space, but bound in water and organic compounds, it is everywhere.
Hydrogen is the simplest element and also the most consequential. It is the fuel of stars, the most abundant matter in the universe, and increasingly the fuel of the green energy transition. Element number 1 has more uses today than at any previous point in history.
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