Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. They are formed because atoms are not happy with the number of electrons that they have. Only the noble gases (column 8A) are content with the number of electrons. They have the optimum number of electrons and don't like to form chemical bonds. The desire of atoms to gain or lose electrons to get a noble gas number of electrons is what leads to chemical bonding.

(It is quite common for chemists to personify the atoms and molecule with which they work! Saying an atom wants an another electron is akin to saying a ball wants to roll down a hill. Later will we examine the energetic and thermodynamic bases of this personification.)

There are three types of chemical bonds:

• Covalent Bonds - atoms are held together by sharing electrons
• Electrostatic (Ionic) Bonds - cations and anions are held together by electrostatic attractions
• Metallic Bonds - occurs in metals (similar to covalent bonds)

Later, you will be able to determine just how ionic or covalent a bond will be, but for now here are some guidelines to follow:

• Bonds amongst non-metal atoms are covalent. (For example, a P-S bond is a covalent bond.)
• Bonds between a non-metal and a metal are ionic (For example, a Na⁺Cl^- bond is ionic.)
• Bonds amongst metal atoms are metallic
• Metalloid--Non-metal bonds are usually covalent
• Metalloid--Metal bonds are usually ionic