Review and Lewis Symbols

Let's begin by reviewing several of the properties of atoms that influence the way that they attach to one another. If you want to review these topics in more depth, go back to Lesson 6.

Tendencies to Gain or Lose Electrons

First, 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.

The ability to lose electrons is related to ionization energy, which you studied in Lesson 6. 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.

High ionization energy means that it is hard to lose electrons. Low ionization energy means that it easy to lose electrons. Thus the overall trend is from most easily losing electrons on the lower left to least easily losing electrons on the upper right.

The ability to gain electrons is also related to the position on the periodic table. 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 noble gases). Ability to gain electrons is greatest at the top of the periodic table, since atoms are smallest there and electrons can be added to lower-energy orbitals.

Practice

Take a moment now to clarify or firm up your thoughts about these atomic properties by doing the following Check your work below.

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 - furthest down and to left

Fe

Sn

3. In each of the following sets, select (circle) the element that will most readily gain electrons.

Cl

Si

Br

F - furthest up and to right

Cl

O

Classification of Elements

In Lesson 6, you also learned about the classification of elements into three broad groups: metals, non-metals, and metalloids.

The metals (in blue below) are found in the left and center of the periodic table, apart from hydrogen. Based on the trends mentioned above, metals tend to be good at losing electrons and bad at gaining them. This will be important in this Lesson as we discuss ionic bonding.

The non-metals (in green below) are found in the upper right triangle of the periodic table. It is also very important to remember that the non-metals include hydrogen! You will find yourself in very bad trouble if you don't remember this fact. Non-metals are generally good at gaining electrons and bad at losing them. Note: this trend does not include the noble gases. Even though they are non-metals, they are already satisfied with the number of electrons they have, and do not wish to either gain or lose them. Once you exclude the noble gases, you realize that the number of chemically active non-metals is really quite small: there are only eleven of them.

Finally, the metalloids (in orange below), also known as semi-metals, follow the diagonal line from boron to astatine. 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 silicon behaves like a nonmetal, but it also has metallic properties. The same is true of the other metalloids. In this class, we will mostly leave the chemistry of the metalloids alone. Where we do encounter metalloids, you should treat them as non-metals.

*Note: there is not good agreement on exactly which elements fall into which categories (for example, germanium and antimony are often considered metalloids). This is because elements lie on a spectrum from metallic to non-metallic, and have a diverse array of properties. Different scientists will take different views on which of those properties are most important for classification.

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 following elements.

Na - metal

Fe - metal

F - nonmetal

P - nonmetal

Si - metalloid

Ar - nonmetal (noble gas)

Lewis Symbols

Generally the electrons that will be involved in bonding (of whatever kind) will be the valence electrons. These are the electrons in the outermost energy level of an atom. Thus, for silicon, which has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p², the valence electrons are the 3s and 3p sublevels. This means silicon has four valence electrons.

For representative elements, the number of valence electrons matches the group number (using the roman numeral-letter system). So silicon has four valence electrons since it is in group IVA.

Take a moment to practice this skill: determine the number of valence electrons in strontium and sulfur as well.

Because elements in the same group have the same number of valence electrons, their Lewis symbols will also look the same. For example, the symbols for nitrogen, arsenic, and bismuth would look the same as the one for phosphorus, just with different letters in the middle.

Practice drawing the following Lewis symbols now: potassium, neon, iodine, and selenium. You can find more opportunities for practice in your lab workbook.