Atomic Structure and the Elements The basic structural unit of matter is the atom. Each atom is composed of a positively charged nucleus, surrounded by a sufficient number of negatively charged electrons so that the charges are balanced. The number of electrons identifies the atomic number and the element of the atom. There are slightly more than 100 elements, and these elements are the chemical building blocks of all matter.

Maximum number of electrons in an orbit = 2n2 where n identifies the orbit, with n = 1 closest to the nucleus.

Bonding Between Atoms and Molecules Thus, we have two types of bonding: (1) primary bonds, generally associated with the formation of molecules; and (2) secondary bonds, generally associated with attraction between molecules. Primary bonds are much stronger than secondary bonds.