ABSTRACT
All matter is made up of atoms, each of which has an essentially similar structure. All atoms are formed of small, dense, positively charged nuclei, typically some 10−14 m in diameter, orbited at much larger distances (about 10-10 m) by negatively charged, very light particles. The atom as a whole is electrically neutral. Note that because matter consists mainly of empty space, radiation may penetrate many atoms before a collision results.
