Atoms are the smallest subject of matter or life. They are 4 thousand millionths of an inch across.  An atom weighs about 4 trillionths  of a trillionth of an ounce.

If you split an atom it makes a bomb. That bomb is the atomic bomb.  It was invented in 1919 in New Zealand by British  physicist Emest Rutherford. The word atomic comes from the word atom.

Click here for a diagram of an atom: http://www.chem4kids.com/atoms/structure.html