1. Write the Lewis symbols for atoms and ions.

Lewis Symbols. Ionic and covalent bonds are important types of chemical bonds. In this chapter you will learn to use electron configurations and the periodic table to predict the type and the number of bonds an atom of a particular element can form. Electron configurations can be used to write the Lewis dot symbols of the representative elements. A Lewis dot symbol of an element consists of the chemical symbol with one or more dots placed around it. Each dot represents a valence electron. The orbital diagram and the Lewis symbol for the fluorine atom are shown in Figure 9.1. Fluorine has 7 electrons in its outermost principal energy level (n = 2), and therefore has 7 dots in its Lewis symbol.

Click on the orbital diagram below to reveal the Lewis symbol.

Figure 9.1 Orbital diagram and Lewis symbol for the fluorine atom.

The Lewis dot symbols and the electron configurations of the outermost electrons of elements in the third period are as follows:

3s1	3s2	3s23p1	3s23p2	3s23p3	3s23p4	3s23p5	3s23p6

Click on each electron configuration above to get the Lewis symbol.

For representative elements, the number of valence electrons is the same as the group number.

Write Lewis symbols for the following elements:

1. Ca

2. O

   S

   Se

             Correct!
   
   Click a Hint button for help.
   
   

The representative metals form ions by losing all of their valence electrons. Lewis symbols can be used to represent the formation of positive magnesium and aluminum ions as follows:

The nonmetal elements form negative ions by acquiring electrons until they are isoelectronic with a noble gas atom. Ions of nonmetal have 8 electrons in their valence shell.

Sulfide and chloride ions, for example, have net charges of –2 and –1 because the atoms needed 2e^– and 1e^–, respectively, to become isoelectronic with the noble gas argon.

Write Lewis symbols for the following ions:

1. Ca²⁺

   	+	Ca2+

     Correct!

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2. Se^2–

   	1-	2-

     Correct!

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1. Removing two electrons (dots) from gives simply Ca²⁺ as the Lewis symbol of a calcium ion. No electrons are shown around the Ca²⁺ symbol because this ion has lost its valence shell electrons.
2. Adding two electrons to gives ^2– as the Lewis symbol for a selenide ion.

Complete the following questions to check your understanding of the material. Select the check button to see if you answered correctly.

1. Write Lewis dot symbols for atoms of the following elements:
1. Mg
2. Se
3. Al
4. Br
5. Xe
2. Write Lewis dot symbols for the following ions:
1. K⁺
2. S^2–
3. N^3–
4. I^–
5. Sr²⁺