Name: electronegativity and polar bonds
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 54 s
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K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

Electronegativity

Los no metales forman enlaces covalentes al compartir electrones. Pero, estos electrones se comparten por igual entre ambos átomos, o un átomo atrae los electrones más que el otro? El modelo de Lewis describe todos los enlaces covalentes como electrones que se comparten por igual;Sin embargo, este no es siempre el caso.Por ejemplo, si se coloca nitrógeno gaseoso en un campo eléctrico, se orientará igualmente entre los polos. Pero cuando se coloca cloruro de hidrógeno gaseoso, una molécula neutra, en un campo eléctrico, el hidrógeno se orienta hacia el cátodo y el cloro hacia el ánodo, lo que indica que el hidrógeno tiene una carga parcial positiva y el cloro una carga parcial negativa. La capacidad de un átomo para atraer electrones hacia sí mismo se llama electronegatividad.Por lo tanto, se dice que el cloro es más electronegativo que el hidrógeno, atrayendo los electrones compartidos hacia sí mismo, mientras se resiste a la eliminación de sus propios electrones. Sin embargo, esto no hace que el enlace sea iónico. En un enlace iónico, los electrones se transfieren de metales a no metales, mientras que en el ácido clorhídrico, los electrones se comparten de manera desigual.La densidad de electrones es mayor en el cloro que en el átomo de hidrógeno formando un enlace covalente polar. Cuanto mayor sea la diferencia de electronegatividad entre dos átomos, más polar será el enlace. Por lo tanto, además de los enlaces covalentes o iónicos no polares, los enlaces covalentes polares se encuentran en una gran variedad de compuestos.El químico estadounidense Linus Pauling estudió las energías necesarias para romper enlaces en moléculas como el cloro diatómico o el hidrógeno. Estableció una escala de electronegatividad basada en datos termoquímicos, que ayuda a predecir los tipos de enlaces. La electronegatividad está asociada con la energía de ionización y la afinidad electrónica de los átomos.En la tabla periódica, los valores de electronegatividad aumentan de izquierda a derecha:los metales son menos electronegativos en comparación con los no metales, con excepción de los metales de transición. Además, los valores de electronegatividad disminuyen en la columna y al aumentar el tamaño atómico, porque los átomos son menos capaces de atraer electrones hacia sí mismos. El flúor, el elemento más electronegativo, tiene la electronegatividad asignada arbitrariamente un valor de 3, 98.El francio, por otro lado, es el elemento menos electronegativo con un valor de electronegatividad de 0, 7. La electronegatividad no tiene unidad;no se puede determinar experimentalmente.

electronegatividad

La electronegatividad es la propiedad de los átomos del enlace que determina si un enlace es no polar o covalente polar.  
 
 Los valores de electronegatividad de los elementos fueron propuestos por uno de los químicos más famosos del siglo XX: Linus Pauling. Pauling investigó las energías requeridas para romper enlaces en moléculas heteronucleares como el hidrógeno y el fluoruro. Basándose en los valores, propuso que la energía requerida para romper un enlace será el promedio de energías de enlace de H2 (436 kJ/mol) y F2 (155 kJ/mol), es decir, 296 kJ/mol. Sin embargo, la energía de enlace obtenida experimentalmente de HF es de 565 kJ/mol, que es mucho más alta que el valor previsto. Para dar cuenta de esta diferencia, Pauling sugirió que el enlace debe tener un carácter iónico, que está determinado por el concepto de electronegatividad. 
 
 La electronegatividad es una medida de la tendencia de un átomo a atraer electrones (o densidad electrónica) hacia sí mismo. 
 
 La electronegatividad determina cómo se distribuyen los electrones compartidos entre los dos átomos de un enlace. Cuanto más fuertemente atrae un átomo a los electrones en sus enlaces, mayor es su electronegatividad. Los electrones en un enlace covalente polar se desplazan hacia el átomo más electronegativo; por lo tanto, el átomo más electronegativo es el que tiene la carga negativa parcial. Cuanto mayor sea la diferencia en la electronegatividad, más polarizada será la distribución de los electrones y más grandes serán las cargas parciales de los átomos.
 
 <h4>Electronegatividad y la Tabla Periódica</h4>
 
 <ul>
 <li>La electronegatividad aumenta de izquierda a derecha en un período de la tabla periódica y disminuye al descender en un grupo.  </li>
 <li>Los valores de electronegatividad obtenidos por Pauling siguen tendencias periódicas predecibles, con las electronegatividades más altas hacia la parte superior derecha de la tabla periódica.</li>
 <li>Así, los no metales, que se encuentran en la parte superior derecha, tienden a tener las electronegativities más altas, siendo el flúor el elemento más electronegativo de todos (EN = 4,0).  </li>
 <li>Los metales tienden a ser elementos menos electronegativos, y los metales del grupo 1 tienen las electronegatividades más bajas. </li>
 <li>Los gases nobles se excluyen de la lista de electronegatividad porque estos átomos generalmente no comparten electrones con otros átomos ya que tienen una capa de valencia llena. (Si bien existen compuestos de gases nobles como el XeO2, sólo pueden formarse en condiciones extremas, y por lo tanto no encajan perfectamente en el modelo general de la electronegatividad.)</li>
 </ul>
 
 <h4>Electronegatividad versus afinidad electrónica</h4>
 
 Tenga cuidado de no confundir electronegatividad y afinidad electrónica. La afinidad electrónica de un elemento es una cantidad física mensurable, a saber, la energía liberada o absorbida cuando un átomo aislado en estado gaseoso adquiere un electrón, medido en kJ/mol. La electronegatividad, por otro lado, describe la fuerza con que un átomo atrae electrones en un enlace. Es una cantidad sin dimensiones que se calcula, no se mide. Pauling obtuvo los primeros valores de electronegatividad comparando las cantidades de energía requeridas para romper diferentes tipos de enlaces. Eligió una escala relativa arbitraria que oscilaba entre 0 y 4.
 
 Este texto es adaptado de<a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Química 2e, Sección: 7.2 Enlace Covalente.</a>

Electronegatividad

El hecho de que un enlace sea no polar o covalente polar está determinado por una propiedad de los átomos de enlace llamada electronegatividad. 

Los valores de electronegatividad de ...

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electronegativity and polar bonds

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond.

Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The experimental bond energy of HF was much higher, at 565 kJ/mol, which suggested the bond had some ionic character.

In a polar covalent bond, the shared electrons shift toward the more electronegative atom. That atom carries the partial negative charge. The larger the electronegativity difference between two atoms, the more the electrons are pulled to one side, and the larger the partial charges become.

Electronegativity follows clear periodic trends. It increases from left to right across a period and decreases down a group. As a result, the highest values are found toward the upper right of the periodic table, especially among nonmetals. Fluorine is the most electronegative element, with a value of 4.0, while group 1 metals have the lowest values. Noble gases are usually left off electronegativity lists because they already have full valence shells and usually do not share electrons. Some noble gas compounds, such as XeO2, can form only under extreme conditions.

Do not confuse electronegativity with electron affinity. Electron affinity is the measurable energy released or absorbed when an isolated gas-phase atom gains an electron. Electronegativity is different. It describes how strongly an atom attracts electrons in a bond, so it is calculated rather than measured. Pauling placed these values on an arbitrary relative scale from 0 to 4.

Electronegativity and Polar Bonds

types of chemical bonds

Chemical Bonding and Bond Properties

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O. Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence...

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Valence Electrons, Lewis Symbols, and Bonding

Chemical bonds form when atoms or ions interact in ways that lower the potential energy of a molecule. Gilbert N. Lewis created a simple model to show bond formation using valence electrons, the electrons in the outer shell. In this model, electrons are shared or transferred to help atoms reach a stable electron configuration. The Lewis model helps describe two common bond types. An ionic bond forms when electrons move from a metal to a nonmetal. A covalent bond forms when two nonmetals share...

electronegativity

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond. Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The...

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Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound. For ionic crystals, lattice energy follows a pattern based on charge and ion size. The...

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Bond polarity depends on electronegativity, the ability of an atom to attract shared electrons. The absolute value of the electronegativity difference, or ΔEN, gives a rough guide to bond type. When the difference is very small or zero, the bond is covalent and nonpolar. When it is larger, the bond may be polar covalent or ionic. Examples show how this works in real compounds. H–H has a ΔEN of 0, so it is nonpolar. H–Cl has a ΔEN of 0.9, so it is polar covalent. Na–Cl has a ΔEN of 2.1, so it...

lewis structures of molecular compounds and polyatomic ions

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Drawing Lewis structures starts with counting valence electrons and building the atom arrangement step by step. Valence electrons are the outer-shell electrons that help show how atoms bond. For ions, a positive charge means one electron is removed for each plus sign, and a negative charge means one electron is added for each minus sign. The next step is to sketch the skeleton structure. The least electronegative atom usually goes in the center, while hydrogen is almost never central. Fluorine...

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Resonance forms in Lewis structures help explain molecules and ions that cannot be shown correctly with just one drawing. In nitrite ion, NO2−, the Lewis structure can be drawn in two ways. The N-O and N=O bonds switch positions in the two drawings, but the atoms stay in the same arrangement. If nitrite really had one single bond and one double bond, the two bond lengths should be different. A double bond is shorter and stronger than a single bond between the same atoms. Experiments show that...

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Lewis structures can sometimes show more than one reasonable arrangement for a molecule or polyatomic ion. Formal charge helps chemists choose the best Lewis structure when that happens. It is a useful way to compare possible structures in chemistry. Formal charge is the hypothetical charge an atom would have if bonding electrons were shared evenly between the atoms. It can also be found by starting with the valence electrons of the neutral atom, subtracting the nonbonding electrons, and then...

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Electron sea model explains how metallic bonding holds metals together. In this model, most metal atoms do not have enough valence electrons to form ionic or covalent bonds in the usual way. Their valence electrons are held loosely because metals have low electronegativity, and their ionization energy is low, so electrons are removed easily. When a metal atom loses these outer electrons, it becomes a positively charged metal ion. The freed electrons form a delocalized electron cloud around...

key terms and concepts

Learn how electronegativity explains polar covalent bonds, Pauling’s bond-energy idea, periodic trends, and the difference from electron affinity.

Electronegativity and Polar Bonds | JoVE K12

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Electronegativity and Polar Bonds

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