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Electronegativity: Trends Among Groups and Periods of the Periodic Table

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  • 0:05 Introduction
  • 0:28 Electronegativity
  • 1:48 Group Trends
  • 3:32 Periodic Trends
  • 5:19 Lesson Summary
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Lesson Transcript
Instructor: Kristin Born

Kristin has an M.S. in Chemistry and has taught many at many levels, including introductory and AP Chemistry.

How is fluorine like a child that doesn't share his or her toys? Find out in this video on electronegativity where we will discuss group and periodic trends among the elements.

Introduction

When you hear the word 'bonding,' what comes to mind? Maybe you think of spending time with your family or going to a baseball game with your buddies. Now think back to when you were a kid, and you were bonding with your friends. At this age, you were probably taught to share your toys, and some of you may have been better at sharing than others. Atoms are no different.

Electronegativity

As you move down a group, the atomic radius increases.
Group 2 Alkaline Earth Metals

When atoms bond with each other to form molecules, they share their electrons. This sharing of electrons is really what creates the bond. Just like children sharing toys unequally, some atoms are going to be better at sharing electrons than others. Some will give up their electrons completely, some will share equally and some will not so much share but instead take other atoms' electrons completely. This unequal sharing of electrons in a bond is due to differences in electronegativity.

Electronegativity is the ability an atom has to attract other electrons. Atoms that have high electronegativities will attract more electrons and may even steal from other atoms. Atoms with low electronegativities will share the most, sometimes to the point of losing their own electrons. Try to remember it this way: You maybe didn't want to play with the kid that took your toys because it brought about a negative feeling of losing something you liked. In 'atom speak,' these kids have a very high electronegativity. So, what makes one atom more electronegative than another? The answer lies in its atomic structure (of course), and just like several other properties of elements, the periodic table has distinct trends in electronegativity.

Group Trends

Just to review, groups on the periodic table are just columns. Let's compare atoms in Group 2: the alkaline earth metals. As you move down from beryllium to radium, what happens to the size of an atom? Well, the atomic radius increases as you move down a group because of the increase in the number and size of the energy levels, so the valence electrons in each atom are getting farther and farther away from the nucleus. The nucleus has quite an effect on pulling those negative electrons in with its positive charge.

Electronegativity increases as you go across a period.
Period Electronegativities

So, which atoms do you think will more easily pull in electrons? Atoms that are tiny and have valence shells close to the nucleus or atoms that are large and have valence shells a great distance from the nucleus? Well, the closer to the nucleus electrons can get, the more pull that nucleus will have, so the smaller atoms are going to pull in electrons a lot more easily than the larger atoms.

If you have ever held two magnets with the north end of one facing the south end of another, you may have felt this pull. The closer the two magnets got, the greater their attraction for each other. You may have had to use some muscles just to keep them apart. However, as you moved them away from each other, you stopped feeling that pull they had on each other.

The same goes for protons and electrons. Yes, they are attracted, but the farther and farther away from the nucleus you get, the less that attraction is. So, as you move down a group on the periodic table, the electronegativity decreases, and atoms have a more difficult time attracting electrons.

Periodic Trends

Next, we're going to compare the electronegativities of elements in the same period. A period is a row on the periodic table. As you move across a row, you will find a similar trend in electronegativities as you did when you went down a column. Smaller atoms are going to have larger electronegativities. Keep in mind as you move across the table, the number of energy levels the electrons are in will stay the same, so the valence electrons will all be in the same energy level. However, the number of protons increases as you move across the table. Not only does this reduce the size of the atom (by pulling in the electrons it does have), but it attracts electrons from atoms bonded to it.

Noble gases have the lowest electronegativity.
Noble Gases

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