Use This Electronegativity Chart to Predict Bond Type and Reactivity

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Key Points

  • Electronegativity is the tendency of an atom to attract electrons
  • We can use it to predict the bond type, chemical reactivity and physical properties of a compound
  • Bonds go from nonpolar to covalent to ionic as the electronegativity difference increases

Because Chemistry is the study of how matter interacts, there are many theories and techniques involved in predicting the properties of atoms, molecules and compounds. Ever since theirexistence was proven, scientists have been interested in studying their properties. Even more recently, much attention has been paid tosmashing particles together,seeinghow they re connectedand how they canproduce light. But one of the core principles of chemistry, which was developed more than 60 years earlier, is the idea ofelectronegativity, as this has a great bearing on chemical behavior and reactivity.

Of course, there s a lot more to how chemicals behave than just electronegativity, but it s a good starting point for making fairly accurate predictions. To this end, we re going to provide you with a simple electronegativity chart, based on the periodic table, that you can use to get an idea of how your particular compound is going to behave, and the types of bonds it may have. Without further ado, let s dive in.

What is Electronegativity?

Given the name, you may be able to make an educated guess about what electronegativity is all about. In simple terms, electronegativity is the tendency of an atom to attract electrons to itself when forming a bond. In essence, an atom draws or takes the electrons from the other atom with a lower electronegativity. The relative values for each element come from the Pauling electronegativity scale, which Linus Pauling developed. He built upon the Valence Bond Theory to further establish the connection between chemical properties. The electronegativity greatly affects how elements bond. Therefore, we can use it to predict how a compound will behave and react under different conditions.

What Factors Affect Electronegativity?

When it comes to determining electronegativity, the situation isn t that simple. There are a lot of things that influence the electronegativity of an element, and the values we use are relative measurements. The biggest factors are the number of protons in the nucleus, as well as the distance of the valence (outer shell) electrons to the nucleus. Generally, the bigger this distance, i.e. the more shells the element has, the lower the element s electronegativity. This is due to electron shielding, where the attraction between the electrons and the nucleus is relatively weaker. As such, the nucleus can t attract electrons as much as an element with a shorter distance. Conversely, the more protons an element s nucleus has, the higher the electronegativity.

Electronegativity can t be measured directly, as it s based on the relationships between an element s properties. Originally, Pauling based his scale on bond energies and other thermochemical data. By calculating the energy differences in covalent bonds, he was able to create a scale for all elements. All the values are relative to fluorine, which has the greatest value of 4.0.

How to Use an Electronegativity Chart

Electronegativity charts provide a helpful representation of Pauling s electronegativity scale. You can gain an appreciation from a simple glance of the table, as the general trend is that electronegativity increases from left to right, and from bottom to top. As mentioned before, this is because a higher number of protons means greater electronegativity and a greater distance from the nucleus to the valence electrons means lower electronegativity. The proton number increases from left to right, and the atom size (and therefore the distance) decreases from bottom to top. That s why we see this trend.

If you want to calculate the electronegativity of your molecule, you need to determine it for every bond in the molecule. To do this, simply take the electronegativity of the bonded elements and calculate the difference. In general terms, a difference of less than 0.5 shows a nonpolar bond, where elements share electrons equally. A difference of 0.5 to 1.7 indicates a polar covalent bond, where electrons are shared unequally. When the difference is larger than 1.7, the bond is usually ionic. This is where one atom basically takes the electron completely from the other atom.

However, it s important to note that these values are relative, and there are many exceptions to the rule. For instance, the atoms in ammonia (NH3) and HF have a difference of 0.9 and 1.9 respectively, yet they bond in a polar covalent fashion. Another useful rul is that nonmetals tend to bond covalently, whereas metals and nonmetals tend to bond ionically.

electronegativity chart
Simple electronegativity chart for predicting the behavior of molecules.

Using the Chart An Example

We ve covered the basics of electronegativity and how we can use the chart. So, let s proceed with an example to demonstrate.

Let s continue with the NH3 and HF molecules. We can see that the electronegativities for N, H and F are approximately 3.04, 2.20 and 3.98 respectively. Therefore, we d expect a difference of 0.84 for the N-H bonds, and a difference of 1.78 for the H-F bond. Using our rough rule, this would indicate a likely polar covalent bond for NH3 and an ionic bond for HF. However, as previously mentioned, this isn t the case in reality, as the H-F bond is also polar covalent. If we take into consideration that H and F are nonmetals, this makes it less likely that the bond is ionic.

As another example, let s look at two nonmetal-metal compounds, i.e. MnI2 and NaCl. The difference in the Na-Cl bond is 2.23, whereas the difference for the Mn-I bond is 1.11. This could suggest that NaCl will bond ionically, whereas MnI2 could bond in a polar covalent fashion. However, in practice, both compounds form ionic bonds, since they re nonmetal-metal compounds. Therefore, it s best to take into account the type of elements in the molecule as well as their electronegativities.

What Can We Predict Using the Electronegativity Chart?

As mentioned, you can use this chart to predict a molecule s bond type, but this isn t a fail-proof method. Aside from this, the chart can help determine an element s electronegativity. This can give us information about its polarity and how may it react, as well as about physical aspects. This includes solubility, and boiling and melting points.

Wrapping Up

In summary, electronegativity charts aren t a 100% certain method for determining a molecule s behavior. But they re a very useful tool for making some predictions. By considering the electronegativity difference between two atoms in a compound, we can gain a fairly good picture of how they may be bonded together. We can also predict the general reactivity and polarity of an element.

As well as this, we can get an idea of their physical properties. In general, electronegativity increases from left to right in the periodic table, and from bottom to top. This is because the electrons are less attracted as the nucleus-electron distance increases. Likewise, the electrons are more strongly attracted as the number of nuclear protons increases. Since atom size increases from top to bottom, and proton number from left to right, we see this trend. Electronegativity values are relative to fluorine, which is has the greatest value of 4.0.

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