Lesson 7: Review
Let's begin by reviewing several of the properties of atoms that influence the way that they attach to one another. These are the valence electrons represented by Lewis diagrams, the tendencies of atoms to gain and lose electrons, and the classification of atoms into the categories of metals and nonmetals (and inert gases).
I suggest you take a look at exercises 1, 2, and 3 in your workbook. If you have no trouble with those exercises, move on to the next section of this lesson ("Bonding Between Atoms"). If you need additional review, continue with this "Review" section.
Lewis Diagrams | Tendencies to Gain or Lose Electrons | Classification of Atoms
Lewis Diagrams
Generally the electrons that will be involved in bonding (of whatever kind) will be the valence electrons. These are the electrons on the outer perimeter of an atom. The number of valence electrons for an atom is often, but not always, determined from the position of that element on the periodic table.
A handy way to illustrate these valence electrons is to use Lewis diagrams, also called electron dot diagrams. These diagrams show the symbol of the element with as many dots around it as there are electrons in the outermost energy level. For example, boron with its electron configuration of 1s22s22p1 has three valence electrons and the Lewis diagram is the symbol B with three dots around it, representing those three valence electrons. Lewis diagrams are useful and easy to draw for the representative elements, which are the "A" Group metals and nonmetals. However, because of the overlapping energy sublevels, these electron dot diagrams become useless for the transition metals, so we won't bother with Lewis diagrams for them. |
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Practice
I'd like you to get some practice by drawing electron dot diagrams for these elements now (or by doing exercise 1 in your workbook).
| Na | Mg | Fe | As | F | Ne |
Answers
Let's go through those quickly. You should have had only one real problem. As you can see, sodium has one dot and magnesium has two. Iron is the problem. It is a transition metal so we will not deal with it. Arsenic has five. Fluorine has seven. Neon has eight.
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Tendencies to Gain or Lose Electrons
Next, let's review two atomic properties important to bonding that are related to the position of the element on the periodic table. They are the tendency or ability of atoms to lose electrons and the tendency or ability to gain electrons.
First, let's consider the ability to lose electrons. This is related to ionization energy, which you studied in a previous lesson. The ionization energy, of course, is the amount of energy that it takes to remove an electron from an atom. You have learned that the ionization energies are lowest for the elements down and on the left hand side of the periodic table and increase as you go up and all the way across to the right including the inert gases.
| The ionization energy measures how hard it is to lose or remove an electron. High ionization energy means that it is hard to lose electrons. Low ionization energy means that it easy to lose electrons. The elements on the left side lose their electrons fairly easily and the elements on the right side of the periodic table do not lose their electrons very easily. Taking vertical position on the table into account, the elements that are lower on the table lose electrons more easily and the elements that are higher have a harder time losing electrons. Thus the overall trend is from most easily losing electrons on the lower left to least easily losing electrons on the upper right. Keep that trend in mind. |
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| The ability to gain electrons is also related to the position on the periodic table. You should recall that as you go from left to right on the periodic table, the attraction for electrons increases and the ability to gain electrons increases. This is true all the way across the periodic table except for the inert gases. There is an abrupt drop in the ability to gain electrons when we get to the inert gases. This is because their energy level is full and any additional electrons will have to start a new energy level. |
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Practice
Take a moment now to clarify or firm up your thoughts about these atomic properties by doing the following (same as exercise 2 in your workbook). Check your work on the next page.
1. The phrases "hard to lose electrons" and "easy to gain electrons" are both similar and different. Comment on how they are similar as they pertain to elements on the periodic table. Comment on how they are different.
2. In each of the following sets, select the element that will most easily lose electrons.
| Na, Cl | Mg, Fe | Na, K | Fe, Br | Si, Sn |
3. In each of the following sets, select (circle) the element that will most readily gain electrons.
| Na, Cl | Si, Sn | Cu, Br | N, F | Cl, Br | P, O |
Answers
Hopefully you had little or no problem with these. If you did, please check with the instructor.
1. The phrases "hard to lose electrons" and "easy to gain electrons" are both similar and different. Comment on how they are similar as they pertain to elements on the periodic table. Comment on how they are different.
Generally, elements that find it hard to lose electrons do so for reasons that also make it easy to gain electrons (high effective nuclear charge and low number of energy levels). The exceptions to this generality are the inert gases which find it both hard to lose electrons (because of high effective nuclear charge) and hard to gain electrons (because of a full outer energy level). --Note: there are a variety of correct ways to respond to this question.
2. In each of the following sets, select the element that will most easily lose electrons.
| Na | Mg | K | Fe | Sn |
3. In each of the following sets, select (circle) the element that will most readily gain electrons.
| Cl | Si | Br | F | Cl | O |
Answers
You should have circled K as the element that will most easily lose electrons and F as the element that will most readily gain electrons.
Classification of Atoms
The next thing in our review is to classify the elements into three groups. These three groups are: metals, nonmetals, and inert gases. (The inert gases are nonmetals, but because of their particular chemical properties - specifically their resistance to bonding - we want to highlight them as a special class of nonmetals.) Let's look at where these groups are located on the periodic table and correlate them with the ability to lose and gain electrons. Remember, these characterizations are oversimplifications.
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First, the metals. They are found in the left, center and lower parts of the periodic table (red/pink area). The metals are good at losing electrons, but they are poor at gaining electrons. The net effect is that the metals tend to lose electrons. Second, the nonmetals. They are found on the top and right side of the periodic table (blue area). They include hydrogen. The nonmetals are poor at losing electrons, but they are good at gaining electrons. They gain electrons better than they lose them. So the nonmetals can be characterized by their ability to gain electrons. |
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Third, the inert gases, or the noble gases, as they are sometimes called, are found in the far right column of the periodic table (white area). Sometimes these are included with the nonmetals because they are not metals. However their behavior and properties are different enough from the other nonmetals that we will consider them as a separate classification. They are poor at both losing and gaining electrons. Therefore, for the most part, they neither gain nor lose electrons.
We can also consider a fourth classification, the metalloids (marked with *). The transition from metallic properties and behavior to nonmetallic properties and behavior is not a simple matter of stepping over a line that can be drawn on the periodic table. In some ways germanium behaves like a nonmetal, and arsenic has some metallic properties. These elements along the dividing line between metals and nonmetals sometimes are put in their own classification of metalloids. The entire semiconductor industry is based on the awareness of the special properties of these elements. For our purposes it will be simplest to view these elements as marginal metals and nonmetals and realize that the dividing line between metals and nonmetals is not really as simple as we usually make it out to be. The metalloids are so-so at losing electrons and so-so at gaining electrons.
Practice
To summarize your understanding of differences between these classifications of atoms as they relate to gaining and losing electrons, please take a moment to do the following (same as exercise 3 in your workbook). Answers follow on the next page.
1. Describe in your own words the nature of the following types of atoms:
metals -
metalloids -
nonmetals -
inert gases -
2. Classify each of the folowing elements.
Na -
Fe -
F -
P -
Si -
Ar -
Answers
1. Describe in your own words the nature of the following types of atoms:
metals - elements that lose electrons fairly easily (and do not gain gain electrons easily)
metalloids - elements that neither gain nor lose electrons very easily but can do both in moderation
nonmetals - elements that gain electrons fairly easily (and do not lose electrons easily)
inert gases - elements that find it hard to either gain or lose electrons
2. Classify each of the folowing elements.
Na - metal
Fe - metal
F - nonmetal
P - nonmetal
Si - nonmetal (or metalloid)
Ar - inert gas