My estimated answer :)

Well what is a covalent bond? A covalent bond is a bond where the elements comprising such bonds share the electrons on their outer shell to become so called 'happy'. It's a stable balance of attractive and repulsive forces between atoms when they share said electrons.

The term 'covalent' can be traced back to it's first use in 1919 in reference to bonding by Irving Langmuir in a Journal of the American Chemical Society in his article "The Arrangement of Electrons in Atoms and Molecules".

One of the first really successful theory surrounding covalence in atoms was formulated by G.N Lewis from which his 1902 lab notes had an eventual lead to his classic article "The Atom and the Molecule" in 1916.

Well you have a covalent bond, you also have this thing called an Ionic Bonding. It's a bond involving a metal and a nonmetal ion through that of electrostatic attraction. The metal donates one or more electrons, forming a positively charged ion or cation with a stable electron config. They then form into the nonmetal and form negatively charged ions, or in short anion.

Now what's all this about metallic bonding? Well metallic bonding is a special bonding between those metal types, speically delocalized electrons. These simple are called conductor electrons and are gathered in what's called an "electron sea" within the nuclei of the metal. It's commonly compared to that of molten salts. As chemistry developed into a science it became clear that metals formed the large majority of the Periodic Table of the elements and great progress was made in the description of the salts that can be formed in reactions with acids. With the advent of electrochemistry it became clear that metals generally go into solution as positively charged ions and the oxidation reactions of the metals became well understood in the electrochemical series. A picture emerged of metals as positive ions held together by an ocean of negative electrons.