CHEMICAL BONDING

Atoms of different elements combine to form molecules of a particular substance.  These molecules are held together by forces called "chemical bonds."  There are various types of bonds and the way these bonds are arranged is unique to that compound.  The two major types of bonds between atoms are called ionic  (transfer of electrons) and covalent (sharing of electrons). Some of the other forces that allow molecules to “bond” are called Van der Waals Forces. 

A compound consists of two or more different types of atoms that are chemically bonded. Electrons move around the nucleus of an element in specific and set orbitals. There are a finite number of electrons in each of these orbitals.

For example, halite (NaCl or table salt) is a combination of sodium and chlorine.  Halite crystals grow in a cubic form, which reflects how chlorine and sodium combine. Since a sodium atom is half the size of an atom of chlorine, the two elements form a perfect cubic pattern (see figure).  The sodium and chlorine share electrons making it an ionic substance.  Ionic compounds are weaker than covalent bonds.  That is why when you combine salt in water (H₂O, a covalent bond), the salt dissolved into its ionic state.   Scientists were aware that familiar substances changed their characteristics when performing experiments, but they did not understand until the 1800’s how elements bond and how they break and come back together.