Electronegativity is the property of an atom which increases with its tendency to attract the electrons of a bond. If two bonded atoms have the same electronegativity values as each other, they share electrons equally in a covalent bond. Usually, the electrons in a chemical bond are more attracted to one atom (the more electronegative one) than to the other. This results in a polar covalent bond. If the electronegativity values are very different, the electrons aren't shared at all. One atom essentially takes the bond electrons from the other atom, forming an ionic bond.
Avogadro and other chemists studied electronegativity before it was formally named by Jöns Jacob Berzelius in 1811. In 1932, Linus Pauling proposed an electronegativity scale based on bond energies. Electronegativity values on the Pauling scale are dimensionless numbers that run from about 0.7 to 3.98. The Pauling scale values are relative to the electronegativity of hydrogen (2.20). While the Pauling scale is most often used, other scales include the Mulliken scale, Allred-Rochow scale, Allen scale, and Sanderson scale. Electronegativity is a property of an atom within a molecule, rather than an inherent property of an atom by itself. Thus, electronegativity actually varies depending on an atom's environment. However, most of the time an atom displays similar behavior in different situations. Factors that affect electronegativity include the nuclear charge and the number and location of electrons in an atom. The chlorine atom has a higher electronegativity than the hydrogen atom, so the bonding electrons will be closer to the Cl than to the H in the HCl molecule. In the O2 molecule, both atoms have the same electronegativity. The electrons in the covalent bond are shared equally between the two oxygen atoms. The most electronegative element on the periodic table is fluorine (3.98). The least electronegative element is cesium (0.79). The opposite of electronegativity is electropositivity, so you could simply say cesium is the most electropositive element. Note that older texts list both francium and cesium as least electronegative at 0.7, but the value for cesium was experimentally revised to the 0.79 value. There is no experimental data for francium, but its ionization energy is higher than that of cesium, so it is expected that francium is slightly more electronegative. Like electron affinity, atomic/ionic radius, and ionization energy, electronegativity shows a definite trend on the periodic table.
Electronegativity and ionization energy follow the same periodic table trend. Elements that have low ionization energies tend to have low electronegativities. The nuclei of these atoms don't exert a strong pull on electrons. Similarly, elements that have high ionization energies tend to have high electronegativity values. The atomic nucleus exerts a strong pull on electrons. Jensen, William B. "Electronegativity from Avogadro to Pauling: Part 1: Origins of the Electronegativity Concept." 1996, 73, 1. 11, J. Chem. Educ., ACS Publications, January 1, 1996. Greenwood, N. N. "Chemistry of the Elements." A. Earnshaw, (1984). 2nd Edition, Butterworth-Heinemann, December 9, 1997. Pauling, Linus. "The Nature of the Chemical Bond. IV. The Energy of Single Bonds and the Relative Electronegativity of Atoms". 1932, 54, 9, 3570-3582, J. Am. Chem. Soc., ACS Publications, September 1, 1932. Pauling, Linus. "The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Mode." 3rd Edition, Cornell University Press, January 31, 1960. {"appState":{"pageLoadApiCallsStatus":true},"articleState":{"article":{"headers":{"creationTime":"2016-03-26T21:47:00+00:00","modifiedTime":"2021-07-15T15:03:14+00:00","timestamp":"2022-09-14T18:18:26+00:00"},"data":{"breadcrumbs":[{"name":"Academics & The Arts","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33662"},"slug":"academics-the-arts","categoryId":33662},{"name":"Science","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33756"},"slug":"science","categoryId":33756},{"name":"Chemistry","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33762"},"slug":"chemistry","categoryId":33762}],"title":"Electronegativity and Polar Covalent Bonding","strippedTitle":"electronegativity and polar covalent bonding","slug":"electronegativity-and-polar-covalent-bonding","canonicalUrl":"","seo":{"metaDescription":"What happens when two atoms involved in a chemical bond aren’t the same? The two nuclei “pull” on the electron pair to different degrees.","noIndex":0,"noFollow":0},"content":"Electronegativity is the strength an atom has to attract a bonding pair of electrons to itself. When a chlorine atom covalently bonds to another chlorine atom, the shared electron pair is shared equally. The electron density that comprises the covalent bond is located halfway between the two atoms.\r\n\r\nBut what happens when the two atoms involved in a <a href=\"https://www.dummies.com/education/science/anatomy/4-types-of-chemical-bonds/\" target=\"_blank\" rel=\"noopener\">chemical bond</a> aren’t the same? The two positively charged nuclei have different attractive forces; they “pull” on the electron pair to different degrees. The end result is that the electron pair is shifted toward one atom.\r\n<h2 id=\"tab1\" >Attracting electrons: Electronegativities</h2>\r\nThe larger the value of the electronegativity, the greater the atom’s strength to attract a bonding pair of electrons. The following figure shows the electronegativity values of the various elements below each element symbol on the periodic table. With a few exceptions, the electronegativities increase, from left to right, in a period, and decrease, from top to bottom, in a family.\r\n\r\nElectronegativities give information about what will happen to the bonding pair of electrons when two atoms bond. A bond in which the electron pair is equally shared is called a <i>nonpolar covalent bond</i>. You have a nonpolar covalent bond anytime the two atoms involved in the bond are the same or anytime the difference in the electronegativities of the atoms involved in the bond is very small.\r\n\r\n<img src=\"https://sg.cdnki.com/what-do-you-call-the-bond-that-share-the-same-atom-and-has-the-same-electronegativity-value---aHR0cHM6Ly93d3cuZHVtbWllcy5jb20vd3AtY29udGVudC91cGxvYWRzLzE2ODIwMy5pbWFnZTAuanBn.webp\" alt=\"image0.jpg\" width=\"535\" height=\"268\" />\r\n\r\nNow consider hydrogen chloride (HCl). Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0. The electron pair that is bonding HCl together shifts <strong>toward the chlorine atom</strong> because the chlorine atom has a larger electronegativity value.\r\n\r\nA bond in which the electron pair is shifted toward one atom is called a <i>polar covalent bond</i>. The atom that more strongly attracts the bonding electron pair is slightly more negative, while the other atom is slightly more positive. The larger the difference in the electronegativities, the more negative and positive the atoms become.\r\n\r\nNow look at a case in which the two atoms have extremely different electronegativities — sodium chloride (NaCl). Sodium chloride is ionically bonded. An electron has transferred from sodium to chlorine. Sodium has an electronegativity of 1.0, and chlorine has an electronegativity of 3.0.\r\n\r\nThat’s an electronegativity difference of 2.0 (3.0 – 1.0), making the bond between the two atoms very, very polar. In fact, the electronegativity difference provides another way of predicting the kind of bond that will form between two elements, as indicated in the following table.\r\n<table>\r\n<tbody>\r\n<tr>\r\n<th>Electronegativity Difference</th>\r\n<th>Type of Bond Formed</th>\r\n</tr>\r\n<tr>\r\n<td>0.0 to 0.2</td>\r\n<td>nonpolar covalent</td>\r\n</tr>\r\n<tr>\r\n<td>0.3 to 1.4</td>\r\n<td>polar covalent</td>\r\n</tr>\r\n<tr>\r\n<td>> 1.5</td>\r\n<td>ionic</td>\r\n</tr>\r\n</tbody>\r\n</table>\r\nThe presence of a polar covalent bond in a molecule can have some pretty dramatic effects on the properties of a molecule.\r\n<h2 id=\"tab2\" >Polar covalent bonding</h2>\r\nIf the two atoms involved in the covalent bond are not the same, the bonding pair of electrons are pulled toward one atom, with that atom taking on a slight (partial) negative charge and the other atom taking on a partial positive charge.\r\n\r\nIn most cases, the molecule has a positive end and a negative end, called a <i>dipole</i> (think of a magnet). The following figure shows a couple of examples of molecules in which dipoles have formed. (The little Greek symbol by the charges refers to a <i>partial</i> charge.)\r\n<div class=\"imageBlock\" style=\"width: 535px;\">\r\n\r\n<img src=\"https://sg.cdnki.com/what-do-you-call-the-bond-that-share-the-same-atom-and-has-the-same-electronegativity-value---aHR0cHM6Ly93d3cuZHVtbWllcy5jb20vd3AtY29udGVudC91cGxvYWRzLzE2ODIwNC5pbWFnZTEuanBn.webp\" alt=\"Polar covalent bonding in hydrogen fluoride and ammonia.\" width=\"535\" height=\"242\" />\r\n<div class=\"imageCaption\">Polar covalent bonding in hydrogen fluoride and ammonia.</div>\r\n</div>\r\nIn hydrogen fluoride (HF), the bonding electron pair is pulled much closer to the fluorine atom than to the hydrogen atom, so the fluorine end becomes partially negatively charged and the hydrogen end becomes partially positively charged.\r\n\r\nThe same thing takes place in ammonia, known as\r\n\r\n<img src=\"https://sg.cdnki.com/what-do-you-call-the-bond-that-share-the-same-atom-and-has-the-same-electronegativity-value---aHR0cHM6Ly93d3cuZHVtbWllcy5jb20vd3AtY29udGVudC91cGxvYWRzLzE2ODIwNS5pbWFnZTIucG5n.webp\" alt=\"image2.png\" width=\"33\" height=\"24\" />\r\n\r\nThe nitrogen has a greater electronegativity than hydrogen, so the bonding pairs of electrons are more attracted to it than to the hydrogen atoms. The nitrogen atom takes on a partial negative charge, and the hydrogen atoms take on a partial positive charge.\r\n<p class=\"Tip\">The presence of a polar covalent bond explains why some substances act the way they do in a chemical reaction: because this type of molecule has a positive end and a negative end, it can attract the part of another molecule with the opposite charge.</p>\r\nThis type of molecule can act as a weak electrolyte because a polar covalent bond allows the substance to act as a conductor. So if a chemist wants a material to act as a good <i>insulator</i> (a device used to separate conductors), the chemist would look for a material with as weak a polar covalent bond as possible.","description":"Electronegativity is the strength an atom has to attract a bonding pair of electrons to itself. When a chlorine atom covalently bonds to another chlorine atom, the shared electron pair is shared equally. The electron density that comprises the covalent bond is located halfway between the two atoms.\r\n\r\nBut what happens when the two atoms involved in a <a href=\"https://www.dummies.com/education/science/anatomy/4-types-of-chemical-bonds/\" target=\"_blank\" rel=\"noopener\">chemical bond</a> aren’t the same? The two positively charged nuclei have different attractive forces; they “pull” on the electron pair to different degrees. The end result is that the electron pair is shifted toward one atom.\r\n<h2 id=\"tab1\" >Attracting electrons: Electronegativities</h2>\r\nThe larger the value of the electronegativity, the greater the atom’s strength to attract a bonding pair of electrons. The following figure shows the electronegativity values of the various elements below each element symbol on the periodic table. With a few exceptions, the electronegativities increase, from left to right, in a period, and decrease, from top to bottom, in a family.\r\n\r\nElectronegativities give information about what will happen to the bonding pair of electrons when two atoms bond. A bond in which the electron pair is equally shared is called a <i>nonpolar covalent bond</i>. You have a nonpolar covalent bond anytime the two atoms involved in the bond are the same or anytime the difference in the electronegativities of the atoms involved in the bond is very small.\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/168203.image0.jpg\" alt=\"image0.jpg\" width=\"535\" height=\"268\" />\r\n\r\nNow consider hydrogen chloride (HCl). Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0. The electron pair that is bonding HCl together shifts <strong>toward the chlorine atom</strong> because the chlorine atom has a larger electronegativity value.\r\n\r\nA bond in which the electron pair is shifted toward one atom is called a <i>polar covalent bond</i>. The atom that more strongly attracts the bonding electron pair is slightly more negative, while the other atom is slightly more positive. The larger the difference in the electronegativities, the more negative and positive the atoms become.\r\n\r\nNow look at a case in which the two atoms have extremely different electronegativities — sodium chloride (NaCl). Sodium chloride is ionically bonded. An electron has transferred from sodium to chlorine. Sodium has an electronegativity of 1.0, and chlorine has an electronegativity of 3.0.\r\n\r\nThat’s an electronegativity difference of 2.0 (3.0 – 1.0), making the bond between the two atoms very, very polar. In fact, the electronegativity difference provides another way of predicting the kind of bond that will form between two elements, as indicated in the following table.\r\n<table>\r\n<tbody>\r\n<tr>\r\n<th>Electronegativity Difference</th>\r\n<th>Type of Bond Formed</th>\r\n</tr>\r\n<tr>\r\n<td>0.0 to 0.2</td>\r\n<td>nonpolar covalent</td>\r\n</tr>\r\n<tr>\r\n<td>0.3 to 1.4</td>\r\n<td>polar covalent</td>\r\n</tr>\r\n<tr>\r\n<td>> 1.5</td>\r\n<td>ionic</td>\r\n</tr>\r\n</tbody>\r\n</table>\r\nThe presence of a polar covalent bond in a molecule can have some pretty dramatic effects on the properties of a molecule.\r\n<h2 id=\"tab2\" >Polar covalent bonding</h2>\r\nIf the two atoms involved in the covalent bond are not the same, the bonding pair of electrons are pulled toward one atom, with that atom taking on a slight (partial) negative charge and the other atom taking on a partial positive charge.\r\n\r\nIn most cases, the molecule has a positive end and a negative end, called a <i>dipole</i> (think of a magnet). The following figure shows a couple of examples of molecules in which dipoles have formed. (The little Greek symbol by the charges refers to a <i>partial</i> charge.)\r\n<div class=\"imageBlock\" style=\"width: 535px;\">\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/168204.image1.jpg\" alt=\"Polar covalent bonding in hydrogen fluoride and ammonia.\" width=\"535\" height=\"242\" />\r\n<div class=\"imageCaption\">Polar covalent bonding in hydrogen fluoride and ammonia.</div>\r\n</div>\r\nIn hydrogen fluoride (HF), the bonding electron pair is pulled much closer to the fluorine atom than to the hydrogen atom, so the fluorine end becomes partially negatively charged and the hydrogen end becomes partially positively charged.\r\n\r\nThe same thing takes place in ammonia, known as\r\n\r\n<img src=\"https://www.dummies.com/wp-content/uploads/168205.image2.png\" alt=\"image2.png\" width=\"33\" height=\"24\" />\r\n\r\nThe nitrogen has a greater electronegativity than hydrogen, so the bonding pairs of electrons are more attracted to it than to the hydrogen atoms. The nitrogen atom takes on a partial negative charge, and the hydrogen atoms take on a partial positive charge.\r\n<p class=\"Tip\">The presence of a polar covalent bond explains why some substances act the way they do in a chemical reaction: because this type of molecule has a positive end and a negative end, it can attract the part of another molecule with the opposite charge.</p>\r\nThis type of molecule can act as a weak electrolyte because a polar covalent bond allows the substance to act as a conductor. So if a chemist wants a material to act as a good <i>insulator</i> (a device used to separate conductors), the chemist would look for a material with as weak a polar covalent bond as possible.","blurb":"","authors":[],"primaryCategoryTaxonomy":{"categoryId":33762,"title":"Chemistry","slug":"chemistry","_links":{"self":"https://dummies-api.dummies.com/v2/categories/33762"}},"secondaryCategoryTaxonomy":{"categoryId":0,"title":null,"slug":null,"_links":null},"tertiaryCategoryTaxonomy":{"categoryId":0,"title":null,"slug":null,"_links":null},"trendingArticles":null,"inThisArticle":[{"label":"Attracting electrons: Electronegativities","target":"#tab1"},{"label":"Polar covalent bonding","target":"#tab2"}],"relatedArticles":{"fromBook":[],"fromCategory":[{"articleId":253707,"title":"How to Make Unit Conversions","slug":"make-unit-conversions","categoryList":["academics-the-arts","science","chemistry"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/253707"}},{"articleId":251836,"title":"How to Convert between Units Using Conversion Factors","slug":"convert-units-using-conversion-factors","categoryList":["academics-the-arts","science","chemistry"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/251836"}},{"articleId":251010,"title":"How to Build Derived Units from Base Units","slug":"build-derived-units-base-units","categoryList":["academics-the-arts","science","chemistry"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/251010"}},{"articleId":251005,"title":"How to Do Arithmetic with Significant Figures","slug":"arithmetic-significant-figures","categoryList":["academics-the-arts","science","chemistry"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/251005"}},{"articleId":250992,"title":"How to Add and Subtract with Exponential Notation","slug":"add-subtract-exponential-notation","categoryList":["academics-the-arts","science","chemistry"],"_links":{"self":"https://dummies-api.dummies.com/v2/articles/250992"}}]},"hasRelatedBookFromSearch":true,"relatedBook":{"bookId":282297,"slug":"inorganic-chemistry-for-dummies","isbn":"9781118217948","categoryList":["academics-the-arts","science","chemistry"],"amazon":{"default":"https://www.amazon.com/gp/product/1118217942/ref=as_li_tl?ie=UTF8&tag=wiley01-20","ca":"https://www.amazon.ca/gp/product/1118217942/ref=as_li_tl?ie=UTF8&tag=wiley01-20","indigo_ca":"http://www.tkqlhce.com/click-9208661-13710633?url=https://www.chapters.indigo.ca/en-ca/books/product/1118217942-item.html&cjsku=978111945484","gb":"https://www.amazon.co.uk/gp/product/1118217942/ref=as_li_tl?ie=UTF8&tag=wiley01-20","de":"https://www.amazon.de/gp/product/1118217942/ref=as_li_tl?ie=UTF8&tag=wiley01-20"},"image":{"src":"https://catalogimages.wiley.com/images/db/jimages/9781118217948.jpg","width":250,"height":350},"title":"Inorganic Chemistry For Dummies","testBankPinActivationLink":"","bookOutOfPrint":false,"authorsInfo":"\n <p><p><b>Michael L. Matson</b> is an assistant professor of chemistry at the University of Houston-Downtown where he instructs Inorganic Chemistry. <b>Alvin W. Orbaek</b> is a research assistant at Rice University, Houston, Texas, where he is completing his PhD in chemistry.</p> <p><b>Michael L. Matson</b> is an assistant professor of chemistry at the University of Houston-Downtown where he instructs Inorganic Chemistry. <b><b data-author-id=\"9692\">Alvin W. Orbaek</b></b> is a research assistant at Rice University, Houston, Texas, where he is completing his PhD in chemistry.</p></p>","authors":[{"authorId":9691,"name":"Michael Matson","slug":"michael-matson","description":" <p><b>Michael L. Matson</b> is an assistant professor of chemistry at the University of Houston-Downtown where he instructs Inorganic Chemistry. <b>Alvin W. Orbaek</b> is a research assistant at Rice University, Houston, Texas, where he is completing his PhD in chemistry.</p>","hasArticle":false,"_links":{"self":"https://dummies-api.dummies.com/v2/authors/9691"}},{"authorId":9692,"name":"Alvin W. Orbaek","slug":"alvin-w-orbaek","description":" <p><b>Michael L. Matson</b> is an assistant professor of chemistry at the University of Houston-Downtown where he instructs Inorganic Chemistry. <b>Alvin W. Orbaek</b> is a research assistant at Rice University, Houston, Texas, where he is completing his PhD in chemistry.</p>","hasArticle":false,"_links":{"self":"https://dummies-api.dummies.com/v2/authors/9692"}}],"_links":{"self":"https://dummies-api.dummies.com/v2/books/282297"}},"collections":[],"articleAds":{"footerAd":"<div class=\"du-ad-region row\" id=\"article_page_adhesion_ad\"><div class=\"du-ad-unit col-md-12\" data-slot-id=\"article_page_adhesion_ad\" data-refreshed=\"false\" \r\n data-target = \"[{"key":"cat","values":["academics-the-arts","science","chemistry"]},{"key":"isbn","values":[null]}]\" id=\"du-slot-63221af238bf3\"></div></div>","rightAd":"<div class=\"du-ad-region row\" id=\"article_page_right_ad\"><div class=\"du-ad-unit col-md-12\" data-slot-id=\"article_page_right_ad\" data-refreshed=\"false\" \r\n data-target = \"[{"key":"cat","values":["academics-the-arts","science","chemistry"]},{"key":"isbn","values":[null]}]\" 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But what happens when the two atoms involved in a chemical bond aren’t the same? The two positively charged nuclei have different attractive forces; they “pull” on the electron pair to different degrees. The end result is that the electron pair is shifted toward one atom.
Electronegativities give information about what will happen to the bonding pair of electrons when two atoms bond. A bond in which the electron pair is equally shared is called a nonpolar covalent bond. You have a nonpolar covalent bond anytime the two atoms involved in the bond are the same or anytime the difference in the electronegativities of the atoms involved in the bond is very small. Now consider hydrogen chloride (HCl). Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0. The electron pair that is bonding HCl together shifts toward the chlorine atom because the chlorine atom has a larger electronegativity value. A bond in which the electron pair is shifted toward one atom is called a polar covalent bond. The atom that more strongly attracts the bonding electron pair is slightly more negative, while the other atom is slightly more positive. The larger the difference in the electronegativities, the more negative and positive the atoms become. Now look at a case in which the two atoms have extremely different electronegativities — sodium chloride (NaCl). Sodium chloride is ionically bonded. An electron has transferred from sodium to chlorine. Sodium has an electronegativity of 1.0, and chlorine has an electronegativity of 3.0. That’s an electronegativity difference of 2.0 (3.0 – 1.0), making the bond between the two atoms very, very polar. In fact, the electronegativity difference provides another way of predicting the kind of bond that will form between two elements, as indicated in the following table.
Polar covalent bondingIf the two atoms involved in the covalent bond are not the same, the bonding pair of electrons are pulled toward one atom, with that atom taking on a slight (partial) negative charge and the other atom taking on a partial positive charge.In most cases, the molecule has a positive end and a negative end, called a dipole (think of a magnet). The following figure shows a couple of examples of molecules in which dipoles have formed. (The little Greek symbol by the charges refers to a partial charge.) Polar covalent bonding in hydrogen fluoride and ammonia. In hydrogen fluoride (HF), the bonding electron pair is pulled much closer to the fluorine atom than to the hydrogen atom, so the fluorine end becomes partially negatively charged and the hydrogen end becomes partially positively charged.The same thing takes place in ammonia, known as The nitrogen has a greater electronegativity than hydrogen, so the bonding pairs of electrons are more attracted to it than to the hydrogen atoms. The nitrogen atom takes on a partial negative charge, and the hydrogen atoms take on a partial positive charge. The presence of a polar covalent bond explains why some substances act the way they do in a chemical reaction: because this type of molecule has a positive end and a negative end, it can attract the part of another molecule with the opposite charge. This type of molecule can act as a weak electrolyte because a polar covalent bond allows the substance to act as a conductor. So if a chemist wants a material to act as a good insulator (a device used to separate conductors), the chemist would look for a material with as weak a polar covalent bond as possible. |