Electronegativity: Definition & Trends

Electronegativity: Definition & Trends
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  • 0:01 What Is Electronegativity?
  • 0:51 Trends on the Periodic Table
  • 2:25 Types of Bonds
  • 5:12 Comparison of…
  • 6:18 Lesson Summary
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Lesson Transcript
Instructor: Nissa Garcia

Nissa has a masters degree in chemistry and has taught high school science and college level chemistry.

The attraction of electrons is different depending on the element. This degree of attraction is measured by the element's electronegativity. In this lesson, we will discuss electronegativity, its trends in the periodic table, and bonding.

What Is Electronegativity?

Magnets are attracted to substances that contain iron, such as stainless steel, cobalt and nickel. Other metallic elements, such as copper and aluminum, do not have a strong attraction to magnets. When you try to see if a magnet will stick to other substances, such as wood or rubber, it does not. This means that the degree of attraction of a magnet to different substances varies.

The same can be said about how electrons are attracted to different elements. There are some elements that attract electrons strongly. On the other hand, there are other elements that don't do as good a job at attracting electrons. The property of an element to attract electrons is what we call electronegativity, which is a property that was first described by a scientist named Linus Pauling. If an element can strongly attract electrons, then it means that element has a high electronegativity.

Trends of Electronegativity on the Periodic Table

Linus Pauling not only introduced electronegativity, but he also came up with electronegativity values for each element in the periodic table as we can see here (see video). Below each element's symbol, there is a number that represents the element's electronegativity. For example, hydrogen (H), has an electronegativity of 2.20.

Based on the values of electronegativity depicted in this periodic table (see video), you might notice that there is a general trend for electronegativity. Let's look at some examples.

Looking at the second period at boron (symbolized by the letter B) and carbon (symbolized by the letter C), we see that boron is less electronegative than carbon. You can also see that carbon is more to the right than boron. This follows the electronegativity trend across a period. Moving to Group 17 in the periodic table, continuing the trend, we see that fluorine (symbolized by the letter F) is more electronegative than chlorine (symbolized by the letters Cl).

Now, because most rules or patterns have exceptions, we need to take a look at Group 18, which is a group called noble gases. It is important to mention that their electronegativity values do not follow the trends. This is because these elements already have their orbitals fully filled, which makes them inert (nonreactive); think about these noble gases as dignified, noble people who do not show emotion or reaction as easily. In that sense, these elements in Group 18 are not looking to react with any other elements; they're not looking to attract electrons.

Electronegativity and Types of Bonds

You may be wondering, why are these numbers important? Electronegativity is important because it can help us to predict if the chemical bonds in molecules will be ionic, polar covalent, or nonpolar covalent.

Ionic Bonds

In an ionic bond, electrons are transferred from one element to another. Ionic bonds are specifically between a metal and nonmetal elements that have very different electronegativity values. The electrons will naturally transfer completely to the element with greater electronegativity.

If:
1.) the electronegativity difference is greater than 1.6; and
2.) one element is a metal and the other element is a nonmetal
then we can say that it is an ionic bond.

How do we know if an element is a metal?

Let's go back and take a look at which parts of the periodic table are metals and which are nonmetals (see video). All of the elements to the left of the black lines that look like stairs are metals except for hydrogen (symbolized by the letter H). All of the elements to the right side of the stairs are nonmetals.

Now let's consider an example using elements from both sides of the table (see video). For sodium (symbolized by the letters Na), the electronegativity is 0.93 and for chlorine (symbolized by the letters Cl), it is 3.16. For magnesium (symbolized by the letters Mg), the electronegativity is 1.31. Sodium and magnesium are both metals. Chlorine is a nonmetal, so the bonds are ionic.

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