How Atoms Join Together to Form Molecules

There are three important types of bonds in biological molecules that we must learn: ionic, covalent and hydrogen.

Ionic Bonding: When an atom loses or gains one or more electrons, it becomes positively or negatively charged and is called an ion. In an ionic bond, positive (+) and negative (-) ions are linked by mutual attraction of opposite charges. Table salt , composed of bonding between sodium (Na+) and chlorine (Cl-) ions is an example of an ionic bond. The sodium atom has only one electron in its outermost shell. The chlorine atom has seven electrons in the same shell. Sodium becomes positively charged when it gives up an electron to chlorine. When chlorine accepts the electron, it becomes negatively charged. The oppositely charged ions then attract each other, forming an ionic bond.

Covalent Bonding: A covalent bond holds together two atoms that share one or more pairs of electrons. In a nonpolar covalent bond, atoms share electrons equally. In a polar covalent bond, because atoms share the electron unequally, there is a slight difference in charge between the two poles of the bond. Water is an example of a polar covalent bond.

Hydrogen Bonding: In a hydrogen bond, an atom of a molecule interacts weakly with a hydrogen atom already taking part in a polar covalent bond. These bonds impart structure to liquid water and stabilize nucleic acids and other large molecules.

This animation (Audio - Important) is a good review of the types of bonds.

This website has a good review of chemical bonding. Read the Introduction, then click on Animation. There are four different animations. To get to another animation, click on the Options button. Finish off with the Conclusion and the Quiz.

REVIEW: What is formed when an atom loses or gains an electron?
Answer ion