How to Calculate Electronegativity: 12 Steps

2024 Author: Samantha Chapman | [email protected]. Last modified: 2024-01-17 17:31

Electronegativity, in chemistry, is the measure of the force with which an atom attracts bonding electrons to itself. An atom with high electronegativity attracts electrons to itself with a lot of force, while an atom with low electronegativity has less force. This value allows us to predict how atoms behave when they bond to each other, so it is a fundamental concept for basic chemistry.

Steps

Part 1 of 3: Knowing the Basic Concepts of Electronegativity

Step 1. Remember that chemical bonds are formed when atoms share electrons

To understand electronegativity, it is important to know what a "bond" is. Two atoms within a molecule, which are "connected" to each other in a molecular pattern, form a bond. This means that they share two electrons, each atom providing an electron to create the bond.

The exact reasons why atoms share electrons and bond are a topic beyond the scope of this article. If you want to know more, you can do an online search or browse wikiHow's chemistry articles

Step 2. Learn how electronegativity affects bonding electrons

Two atoms sharing a pair of electrons in a bond do not always contribute equally. When one of the two has a higher electronegativity, it attracts the two electrons towards it. If an element has very strong electronegativity, then it could bring electrons almost completely to its side of the bond by sharing its marginally with the other atom.

For example, in the molecule NaCl (sodium chloride) the chlorine atom has a rather high electronegativity, while that of sodium is rather low. For this reason the bonding electrons are entrained towards chlorine And away from sodium.

Step 3. Use the electronegativity table as a reference

It is a scheme in which the elements are arranged exactly like on the periodic table, except that each atom is also identified with the electronegativity value. This table is featured in many chemistry textbooks, technical articles and even online.

In this link you will find a good periodic table of electronegativity. This uses the Pauling scale, which is the most common. However, there are other ways to measure electronegativity, one of which is described below

Step 4. Memorize the electronegativity trend for easy estimation

If you don't have a table, you can evaluate this characteristic of the atom based on its position in the periodic table. As a general rule:

• Electronegativity tends to to increase as you move towards right of the periodic table.
• The atoms found in the part high of the periodic table have electronegativity greater.
• For this reason, the elements located in the upper right corner have a higher electronegativity than those in the lower left corner.
• Always considering the example of sodium chloride, you can understand that chlorine has a higher electronegativity than sodium, because it is closer to the upper right corner. Sodium, on the other hand, is found in the first group on the left, so it is among the least electronegative atoms.

Part 2 of 3: Finding the Bonds with Electronegativity

Step 1. Calculate the difference in electronegativity between two atoms

When these bond, the electronegativity difference gives you a lot of information about the characteristics of the bond. Subtract the lower value from the upper one to find the difference.

For example, if we consider the HF molecule, we must subtract the electronegativity of hydrogen (2, 1) from that of fluorine (4, 0) and we get: 4, 0-2, 1 = 1, 9.

Step 2. If the difference is less than 0.5, then the bond is non-polar covalent and the electrons are shared almost equally

This type of bond, on the other hand, does not generate molecules with a large polarity. Non-polar ties are very difficult to break.

Let us consider the example of the molecule O₂ who has this kind of connection. Since the two oxygen atoms have the same electronegativity, the difference is zero.

Step 3. If the electronegativity difference is within the range 0.5-1.6, then the bond is polar covalent

These are bonds in which electrons are more numerous at one end than at the other. This causes the molecule to be slightly more negative on one side and slightly more positive on the other, where there are fewer electrons. The charge imbalance of these bonds allows the molecule to take part in certain types of reactions.

A good example of this type of molecule is H.₂O (water). Oxygen is more electronegative than the two hydrogen atoms, so it tends to attract electrons towards it with greater force making the molecule slightly more negative towards its end and slightly more positive towards the hydrogen side.

Step 4. If the difference in electronegativity exceeds the value of 2.0, it is called an ionic bond

In this type of bond, the electrons are completely at one end. The more electronegative atom gains a negative charge and the less electronegative atom acquires a positive charge. This kind of bonding allows the atoms involved to react readily with other elements and can be broken by polar atoms.

Sodium chloride, NaCl, is a great example of this. Chlorine is so electronegative that it attracts both bonding electrons to it leaving the sodium with a positive charge

Step 5. When the difference in electronegativity is between 1, 6 and 2, 0, check for the presence of a metal. If so, then the link would be ionic. If there are only non-metal elements then the bond is polar covalent.

• The category of metals includes most of the elements found on the left and in the center of the periodic table. You can do a simple online search to find a table where the metals are clearly highlighted.
• The previous example of the HF molecule falls within this case. Since both H and F are non-metals, they form a bond polar covalent.

Part 3 of 3: Finding Mulliken's Electronegativity

Step 1. To begin, find the first ionization energy of the atom

Mulliken electronegativity is measured slightly differently than the method used in the Pauling scale. In this case, you must first find the first ionization energy of the atom. This is the energy needed to make an atom lose a single electron.

• This is a concept you will probably need to review in your chemistry textbook. Hopefully this Wikipedia page is a good place to start.
• As an example, suppose we need to find the electronegativity of lithium (Li). On the ionization table we read that this element has a first ionization energy equal to 520 kJ / mol.

Step 2. Find the electron affinity of the atom

This is the amount of energy gained by the atom when it acquires an electron to form a negative ion. Again you should look for references in the chemistry book. Alternatively, do some research online.

Lithium has an electron affinity equal to 60 kJ mol^-1.

Step 3. Solve the Mulliken equation for electronegativity

When you use kJ / mol as a unit of energy, the Mulliken equation is expressed in this formula: EN_Mulliken = (1, 97×10⁻³)(AND_the+ E_{it's at}) + 0, 19. Replace the appropriate variables with the data in your possession and solve for EN_Mulliken.

• Based on our example we have that:

  EN_Mulliken = (1, 97×10⁻³)(AND_the+ E_{it's at}) + 0, 19

  EN_Mulliken = (1, 97×10⁻³)(520 + 60) + 0, 19

  EN_Mulliken = 1, 143 + 0, 19 = 1, 333

Advice

• Electronegativity is measured not only on the Pauling and Mulliken scales, but also on the Allred – Rochow, Sanderson and Allen scales. Each of them has its own equation to calculate electronegativity (in some cases these are quite complex equations).
• Electronegativity has no unit of measurement.