The electron-dot structure (also known as the "Lewis dot structure") for N is shown below:
The red dots represent electrons that comprise the atom's
5 valence electrons.
Recall that the valence (outermost) electrons are those that are involved in chemical reactions of bonding. The rule you should apply to drawing this electron dot structure is to first draw (or imagine) a rectangle around the atom's symbol, letting the rectangle represent the atom's core electrons (not shown), those within the atom's inner (s) shell. Then place one electron on each side. That leaves the remaining electron to be placed on one of the already occupied sides to give the electron pair.
It doesn't matter what side you place this 5th electron, because the final result is the pattern shown above, 3 single dots and one pair of dots, which neatly reveals the bonding power* of N (3) - and the existence of the one electron pair, which predicts special types of reactivity you will probably appreciate in more advanced topics of this element's behavior.
*
The single electrons are more reactive than the electron pair, and will readily form bonds with other atoms, such as H. This allows you to predict that N and H atoms will combine to form NH3.
How do you know there are 5 valence electrons? For the answer, refer to the following partial image of the Periodic Table of the Elements I drew using Word and SnagIT software:
Notice the number-letter labels above each column ("group") of elements, for example "5A." The letter A indicates the groups of "representative" elements, the most common elements studied in general chemistry courses. The numbers before the "A" represents the number of valence electrons surrounding each element's atoms. For example, hydrogen has one valence electron, nitrogen has 5 valence electrons, and oxygen has 6 valence electrons.
Using the rules described above for drawing electron-dot structures, how many single dots and double dots should be drawn around H? Around O? Can you predict the bonding power of each of these atoms? What molecular compounds do you predict would be formed from the reaction of H and H? What molecular compound do you predict would form between combining H atoms and O?
Hints:
Reactions tend to occur that cause the single electrons (dots) to pair up. This occurs because paired electrons are much more stable than single electrons. A strong driving force for a reaction is the going from a less stable state to a more stable state. Hydrogen atoms from H2 molecules (diatomic molecules). H and O atoms combine to form dihydrogen oxide, also known as water!
Summary:
- A very simple set of rules allows you to predict the electron dot structures of the representative elements.
- The electron dot structures are very useful, because they can allow you to predict the bonding power of each representative element.
- They are also useful in guiding your prediction of the compositions of molecules that can form during reactions between their atoms (that is, how many of each element in the molecule).
- In more advanced topics you will also be able to use electron-dot structures to predict the shapes (or geometry) of molecules, including bond angles!
- So, learning the skill of drawing electron-dot structures is very important to mastering chemistry!
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