(BCR) Electron Dot Diagrams Lesson

Electron Dot Diagrams

Diagrams contain a lot of useful information in a compact format.  What does the diagram above tell us? The football play diagrammed above describes the lineup of each player on the team and describes how they will move when the ball is snapped. Diagrams of electrons give similar information about where certain electrons are.  We can mark these electrons and indicate what happens to them when an element reacts.

Recall that the valence electrons of an atom are the electrons that reside in the highest occupied energy level. Valence electrons are primarily responsible for the chemical properties of various elements. The number of valence electrons can be easily determined from the position of the element on the periodic table. Remember from the previous module that within each column, or group, of the table, all the elements have the same number of valence electrons. For elements in groups 1-2 and 13-18, the number of valence electrons is easy to tell directly from the periodic table. This is illustrated in the simplified periodic table shown below.

When examining chemical bonding, it is necessary to keep track of the valence electrons of each atom. Electron dot diagrams (sometimes referred to as Lewis Dot Diagrams) are diagrams in which the valence electrons of an atom are shown as dots distributed around the element's symbol.  Since electrons repel each other, the dots for a given atom are distributed evenly around the symbol before they are paired. The table below shows the electron dot diagrams for the entire second period of elements on the periodic table.  Electron dot diagrams would be the same for each element in the representative element groups. 

For a further explanation of Electron Dot Diagrams as well as some examples to practice, please watch the video below.  

The Octet Rule

The noble gases are unreactive because of their electron configurations. American chemist, Gilbert Lewis (1875-1946), used this observation to explain the types of ions and molecules that are formed by other elements. He called his explanation the octet rule. The octet rule states that elements tend to form compounds in ways that give each atom eight valence electrons. There are two ways in which atoms can satisfy the octet rule. One way is by sharing their valence electrons with other atoms forming Covalent Bonds. The second way is by transferring valence electrons from one atom to another forming Ionic Bonds. Atoms of metallic elements tend to lose all of their valence electrons, which leaves them with an octet from the next lowest principal energy level. Atoms of nonmetallic elements tend to gain electrons in order to fill their outermost principal energy level with an octet.

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