join with another hydrogen atom as a pair, making a molecule. Sometimes it is easy to tell which element a symbol stands for. For example, C stands for carbon and Li stands for lithium.

Each ammonia molecule contains one atom of nitrogen and three atoms of hydrogen. We know this because the hydrogen symbol has a subscript three after it, whereas the nitrogen symbol has no number ...

Hydrogen: The simplest atom, hydrogen, has 1 proton in its nucleus ... This number is usually written above the element symbol on the periodic table. The mass number is called the atomic mass ...

Scientists have just seen for the first time one of the most important physical interactions in our world — the special type of bond called the hydrogen bond that holds our DNA together and ...