Hydrogen is an atom. Atoms are the smallest piece of matter, or anything that takes up space. Atoms are made up of smaller pieces called protons, neutrons and electrons. Atoms are sometimes called elements. Hydrogen is the simplest element---it contains just one proton and one electron.
Hydrogen is the smallest element. Hydrogen is 0.12 nanometres (nm) in diameter. A nanometre is one-billionth of a meter or 1/1,000,000,000 meters. Consider that the width of one strand of hair is 100,000 nm wide. That would mean that about 833,333 hydrogen atoms can fit across the width of one strand of hair.
Hydrogen is one of the most abundant elements in the human body. In the body, hydrogen is mostly found attached to other atoms, such as carbon and oxygen. When two hydrogen atoms combine with one oxygen atom, it makes water. Hydrogen can also combine with chlorine and make hydrochloric acid. Hydrochloric acid can badly burn skin and even burn through clothing, plastic and some metals. But the body can use hydrochloric acid in the stomach to break up food for digestion.
Hydrogen sticks to other atoms through a covalent bond. Covalent bonds are very strong because both atoms want to have the same electrons. The atoms have to share the electrons. Sharing keeps the atoms close together, forming a bond.
Hydrogen is a cheap and effective alternative fuel. It can be used in vehicles, such as cars and trucks, or even to launch the Space Shuttle. When hydrogen is used for fuel in a car, water comes out of the exhaust pipe instead of harmful chemicals. Hydrogen is lighter than air, so it can also be used to fly large passenger balloons called zeppelins. But, hydrogen can catch on fire easily and cause big explosions. It is important to always use hydrogen carefully.
Hydrogen also forms hydrogen bonds. These are not very strong bonds but are very important. One thing hydrogen bonds do is allow very light things to walk or sit on top of water without sinking to the bottom. A water strider, or skater bug, uses the surface tension of water made by hydrogen bonds to move around.