Chemical Bonding

INTRAMOLECULAR BONDS

The first two bonds we will look at are called intramolecular bonds. This means they are found inside molecules; they create the molecule. In both cases, the atoms in the molecule are all trying to find a way to fill their outer electron shells to be stable.

Ionic Bonds

The first way to get a full outer shell is to give away or receive one or more electrons.

  • If an atom has one or two electrons in its outer shell, it will want to give those to another atom.

  • If another atom has six or seven electrons in its outer shell, it will happily receive electrons.

As long as we end with full outer shells, everyone is satisfied. By definition, however, what we have now are not atoms; there is a charge difference between the nucleus and the electron cloud; we have created ions.

  • If an atom has given away electrons, they now have a positive charge, and we call them cations.

  • If an atom has received extra electrons, it now has a negative charge, and we call them anions.

In either case, as long as the outer shells are full, then both atoms are now stable. Since opposites attract, cations and anions are attracted to each other and form our first type of chemical bond called an ionic bond.

NAS 2 Ions and Ionic Bonds: 5 Min

 

Covalent Bonds

Sometimes it just doesn't work out to give or receive electrons, but there's another way to end up with a full outer shell: sharing! Electrons move so fast that atoms can share their electrons, and they count towards both outer shells (again ending up with full shells). Since this only works, if the atoms stay close together, this creates a strong covalent bond.

  • If the atoms share the electrons unequally, the electron will spend more time with one atom than the other; it is called a polar covalent bond. Polar covalent molecules have slightly positive and negative charges and interact easily with any molecule with charge - ions or other polar molecules. Polar molecules are considered hydrophilic as they can easily interact with water.

  • If the atoms share the electrons equally, it is called a nonpolar covalent bond. Molecules with nonpolar covalent bonds do not interact well with any molecules that have charges, including ions and polar covalent molecules. Nonpolar molecules are considered hydrophobic as they do not interact well with water (a polar molecule).

NAS 2 Covalent Bonds: 5:30 Min

 

INTERMOLCULAR BONDING

The third type of bond is referred to as intermolecular bonding. This means the bond is found between molecules, not inside the molecule.

Hydrogen Bonds

A hydrogen bond is an intermolecular bond that holds two polar molecules together, usually between a slightly positive hydrogen of one molecule and a slightly negative atom of another molecule (usually oxygen, nitrogen, or phosphorus). Although these are extremely weak bonds, there are many of them, and together, they can be quite strong. In the image below, note the hydrogen bond between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another water molecule. If you throw water into the air and it forms balls of water, the hydrogen bonds are responsible for this.

 

Image of hydrogen bond

 

Bonds listed in order from strongest to weakest: covalent, ionic, and hydrogen.