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In chemistry, electronegativity is the unit of measurement for the attraction of an atom to an electron in a chemical bond. [1] X Source of Research A highly electronegative atom will attract electrons with a strong force, whereas a low electronegativity atom will attract electrons with a weak force. Electronegativity values are used to predict the ability to form chemical bonds between atoms, so this is an important skill in basic chemistry.
Steps
Basic knowledge of electronegativity
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Chemical bonds arise when atoms share electrons. To understand electronegativity, you must first understand what “bonding” is. Any two atoms that are “connected” to each other in the molecular formula will have a bond between them, meaning they share a pair of electrons and each atom contributes an electron to that bond.
- This article does not cover the exact reason why atoms share electrons and have bonds between them. If you want to learn more, read this article on chemical bonding or the wikiHow article on How to Study Chemical Bonding Properties.
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How does electronegativity affect electrons in a bond? When two atoms share a pair of electrons in a bond, this sharing is not always balanced. When one atom is more electronegative than the other, it pulls the two electrons in the bond closer to it. The very electronegative atom can pull electrons towards it almost completely, and share almost no electrons with the other atom.
- For example, in the NaCl (sodium chloride) molecule, the chlorine atom has a relatively high electronegativity and the sodium atom has a relatively low electronegativity. Hence the electrons are pulled towards the chlorine atom and away from the sodium atom .
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Use the electronegativity lookup table for reference. In the electronegativity table, the chemical elements are arranged in exactly the same way in the periodic table, but each atom has an electronegativity record. This table is printed in many chemistry textbooks, technical literature or on the internet.
- This is the connection that leads to the electronegativity lookup table. Note that this table uses the Pauling electronegativity scale, which is the most common electronegativity scale. [2] X Research Sources However, there are other ways to measure electronegativity, and some of these will be discussed below.
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The atoms are arranged in order of electronegativity for ease of estimation. If you don’t have an electronegativity lookup available, you can estimate the electronegativity of an atom based on its position on the regular periodic table. As a general rule:
- The electronegativity of an atom increases as you move to the right of the periodic table.
- The electronegativity of an atom gets higher as you move up the periodic table.
- Therefore, the atoms in the upper right corner have the most electronegativity, and the atoms in the lower left corner have the least electronegativity.
- In the NaCl example above, you probably know chlorine is more electronegative than sodium because it is located very close to the top right corner of the periodic table. In contrast, sodium is far to the left so it belongs to the group of atoms with low electronegativity.
Determine bond type by electronegativity
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Find out the electronegativity difference between two atoms. When two atoms are bonded together, the difference in electronegativity between the two atoms can tell you the properties of that bond. Subtract the large electronegativity from the small electronegativity to find the difference.
- Taking the HF molecule as an example, we will subtract the electronegativity of fluorine (4,0) from the electronegativity of hydrogen (2,1). 4.0 – 2.1 = 1.9 .
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If the electronegativity difference is less than about 0.5 then the bond is a nonpolar covalent bond in which the electrons are shared almost equally. This type of bond does not form a molecule with a large charge difference between the two ends of the bond. Non-polar bonds are often difficult to break. [3] X Research Sources
- For example, the molecule O 2 has this type of bond. Since two oxygen atoms have the same electronegativity, their difference is zero.
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If the electronegativity difference is between 0.5-1.6 then the bond is a polar covalent bond. These bonds have more electrons at one end than the other. This causes the molecule to have a slightly larger negative charge at the electron end, and a slightly larger net positive charge at the other end. The charge imbalance in the bond allows the molecule to participate in some particular reaction. [4] X Research Sources
- The molecule H 2 O (water) is a good example of this. The O atom is more electronegative than the two H atoms, so it holds the electrons more tightly, and causes the entire molecule to carry a partial negative charge at the O end and a partial positive charge at the H end.
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If the electronegativity difference is greater than 2.0 then the bond is an ionic bond. In this bond, the electrons are located entirely at one end of the bond. The more electronegative atom has a negative charge, and the less electronegative atom has a positive charge. This type of bond allows the atom in it to react well with other atoms, and even to be separated by polar atoms.
- An example is the molecule BaCl (sodium chloride). The chlorine atom has such a large negative charge that it pulls both electrons completely towards it, leaving sodium with a positive charge.
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If the electronegativity difference is in the range of 1.6-2.0, check the metallic element. If there is a metallic element in the bond it is an ionic bond. If no metallic element is present, it is a polar covalent bond.
- Metallic elements include most of the elements located to the left and middle of the periodic table. This page has a table showing which elements are metallic. [5] X Research Sources
- The HF example above falls within this range. Since H and F are not metals, they have polar covalent bonds.
Find electronegativity according to Mulliken
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Find the first ionization energy of the atom. Mulliken electronegativity is a slightly different method of measuring electronegativity than the above Pauling scale method. To find the Mulliken electronegativity for a given atom, find its first ionization energy. This is the energy required for the atom to give away an electron.
- Perhaps you should look up this parameter in the chemical reference literature. This page provides a lookup table that you can use (scroll down to see). [6] X Research Source
- For example, suppose we need to find the electronegativity of lithium (Li). Looking at the table on the above page, we see that the first ionization energy is 520 kJ/mp .
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Find the electron affinity of the atom. This is a unit of measurement of the energy obtained when an atom gains an electron to form a negative ion. You must also look up this parameter in the reference chemistry literature. This page has the learning resources you should be looking for. [7] X Research Sources
- The electron affinity of lithium is 60 kJ mp -1 .
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Solve the electronegativity equation according to Mulliken. When you use kJ/mp for energy, the Mulliken electronegativity equation is EN Mulliken = (1.97×10 −3 )(E i +E ea ) + 0.19 . Plug the values into the equation and solve for EN Mulliken .
- In this example, we will solve the following:
-
- EN Mulliken = (1.97×10 −3 )(E i +E ea ) + 0.19
- EN Mulliken = (1.97×10 −3 )(520 + 60) + 0.19
- EN Mulliken = 1.143 + 0.19 = 1.333
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Advice
- In addition to the Pauling and Mulliken scales, some other electronegativity scales are the Allred–Rochow, Sanderson, and Allen scales. All of these scales have their own equations for calculating electronegativity (some are quite complicated).
- Electronegativity has no units .
X
wikiHow is a “wiki” site, which means that many of the articles here are written by multiple authors. To create this article, 15 people, some of whom are anonymous, have edited and improved the article over time.
There are 7 references cited in this article that you can view at the bottom of the page.
This article has been viewed 79,012 times.
In chemistry, electronegativity is the unit of measurement for the attraction of an atom to an electron in a chemical bond. [1] X Source of Research A highly electronegative atom will attract electrons with a strong force, whereas a low electronegativity atom will attract electrons with a weak force. Electronegativity values are used to predict the ability to form chemical bonds between atoms, so this is an important skill in basic chemistry.
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