Hydrogen

Hydrogen is a chemical element. It is the lightest and simplest of all the elements, and the first one on the periodic table. A hydrogen atom is made of just one proton and one electron. That is as simple as an atom can be. Hydrogen is also the most common element in the whole universe.

At room temperature, pure hydrogen is a gas. It has no color, no smell, and no taste. Two hydrogen atoms usually pair up to make a hydrogen molecule, written as H₂. Hydrogen gas is about 14 times lighter than the air around you. If you filled a balloon with it, the balloon would shoot upward.

Hydrogen got its name from two Greek words meaning "water-maker." When hydrogen burns, it joins with oxygen in the air and makes water. Every drop of water on Earth contains hydrogen. In fact, each water molecule is two hydrogen atoms stuck to one oxygen atom, which is why water is called H₂O.

Stars are giant balls of hydrogen. The Sun is about three-fourths hydrogen by weight. Deep inside the Sun, the pressure and heat are so great that hydrogen atoms smash together and turn into helium. This process, called fusion, is what makes the Sun shine. Every second, the Sun turns about 600 million tons of hydrogen into helium. That is more mass than a small mountain, disappearing into sunlight each second.

Hydrogen is useful on Earth too. Factories use it to make fertilizer for crops. Rockets burn liquid hydrogen as fuel. The main engines of the Space Shuttle ran on it for years. Some cars now use hydrogen to make electricity inside devices called fuel cells. The only thing that comes out the tailpipe is water vapor.

But hydrogen has a dangerous side. It catches fire easily and burns with a nearly invisible flame. In 1937, a giant German airship called the Hindenburg was held up by hydrogen gas. It caught fire while landing in New Jersey and burned in less than a minute. After that, airships switched to helium, which does not burn.

Scientists today are trying to make "green hydrogen" by splitting water using electricity from solar panels and wind turbines. If it works at a large scale, hydrogen could help replace fuels that pollute the air. Researchers still disagree about how big a role it will play. For now, the lightest element in the universe is being asked to do some heavy work.