Chemical Bonds and Bonding

Chemistry Notes and Review

This is a review of notes on chemical bonds and bonding at the high school or 11th grade chemistry level. Chemical bonds are easy to understand if you keep in mind the following properties of atoms and electrons:

• Atoms seek the most stable configuration.
• The Octet Rule states that atoms with 8 electrons in their outer orbital will be most stable.
• Atoms can share, give, or take electrons of other atoms. These are forms of chemical bonds.
• Bonds occur between the valence electrons of atoms, not the inner electrons.

Types of Chemical Bonds

The two main types of chemical bonds are ionic and covalent bonds, but you should be aware of several forms of bonding:

• Ionic Bonds
  Ionic bonds form when one atom takes an electron from another atom.
  Example: NaCl is formed by an ionic bond where sodium donates its valence electron to chlorine. Chlorine is a halogen. All halogens have 7 valence electrons and need one more to gain a stable octet. Sodium is an alkali metal. All alkali metals have 1 valence electron, which they readily donate to form a bond.
• Covalent Bonds
  Covalent bonds form when atoms share electrons. Really, the main difference is the electrons in ionic bonds are more closely associated with one atomic nucleus or the other, which electrons in a covalent bonds are about equally likely to orbit one nucleus as the other. If the electron is more closely associated with one atom than the other, a polar covalent bond may form.
  Example: Covalent bonds form between hydrogen and oxygen in water, H2O.
• Metallic Bond
  When the two atoms both are metals, a metallic bond forms. The difference in a metal is that the electrons could be around any metal atom, not just two atoms in a compound.
  Example: Metallic bonds are seen in samples of pure elemental metals, such as gold or aluminum, or alloys, such as brass or bronze.

Ionic or Covalent?

You may be wondering how you can tell whether a bond is ionic or covalent. You can look at the placement of elements on the periodic table or a table of element electronegativities to predict the type of bond that will form. If the electronegativity values are very different from each other, an ionic bond will form. Usually the cation is a metal and the anion is a nonmetal. If the elements both are metals, expect a metallic bond to form. If the electronegativity values are similar, expect a covalent bond to form. Bonds between two nonmetals are covalent bonds. Polar covalent bonds form between elements that have intermediate differences between the electronegativity values. Usually on a test, you'll be given clear examples of ionic compounds or covalent compounds or you'll need to pick the molecule most likely to form polar covalent bonds from a list.