Name: bond order and molecular orbitals
Uploaded: 2023-04-30T18:28:31.000Z
Duration: 2 min 40 s
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

4.2.1 9C.3.2.1.2

MO Theory and Covalent Bonding

La teoría de orbitales moleculares describe la distribución de electrones a través de una molécula en lugar de localizarlos en enlaces específicos entre átomos.
La interferencia constructiva entre orbitales atómicos en fase corresponde a una mayor densidad de electrones entre los núcleos cargados positivamente, lo que hace que la molécula sea más estable. Este orbital molecular de enlace es más bajo en energía que cualquiera de los orbitales atómicos originales.
La interferencia destructiva entre orbitales atómicos desfasados corresponde a una menor densidad de electrones en un plano nodal entre los núcleos, lo que hace que la molécula sea menos estable. Este orbital molecular antienlazante es más alto en energía que los orbitales atómicos y está marcado con una estrella o un asterisco.
Los orbitales moleculares se clasifican por la forma en que los orbitales atómicos se superponen. La combinación frontal de orbitales atómicos a lo largo del eje internuclear, como la superposición entre dos orbitales s o dos orbitales p de extremo a extremo, da como resultado orbitales moleculares sigma. La densidad de electrones del orbital sigma se centra alrededor del eje internuclear.
La superposición lateral, como la superposición lateral de dos orbitales p, da como resultado orbitales moleculares pi. Aquí, la densidad de electrones se concentra en lados opuestos del eje internuclear.
La orientación de los tres orbitales p diferentes significa que, por lo general, un par se superpone de extremo a extremo y los otros dos pares se superponen de lado. Los orbitales de enlace pi suelen tener la misma energía, o degenerarse, al igual que los orbitales de enlace pi.
La teoría de orbitales moleculares predice la estabilidad de los enlaces covalentes a partir del orden de enlace de la molécula, que es el número de electrones en los orbitales de enlace menos el número de electrones en los orbitales antienlazantes dividido por dos.
Un orden de enlace mayor que cero indica que pueden existir uno o más enlaces covalentes, mientras que un orden de enlace de cero significa que los enlaces no deberían existir.
La teoría de orbitales moleculares también es útil para moléculas poliatómicas como el benceno. El modelo de Lewis del benceno no puede representar con precisión sus electrones deslocalizados, mientras que la teoría de orbitales moleculares asigna esos electrones a tres orbitales moleculares de enlace pi que cubren todo el anillo de carbono.

Este texto es una adaptación de <a href="https://openstax.org/books/chemistry-2e/pages/8-4-molecular-orbital-theory">Openstax, Chemistry 2e, Section 8.4 Molecular Orbital Theory</a>.

teoría mo y enlace covalente

La teoría de los orbitales moleculares describe la distribución de los electrones en las moléculas de manera similar a la distribución de los electrones en los orbitales atómicos. La región del espacio en la que es probable que se encuentre un electrón de valencia en una molécula se llama orbital molecular. Matemáticamente, la combinación lineal de orbitales atómicos (LCAO) genera orbitales moleculares. Las combinaciones de funciones de onda orbitales atómicas en fase dan como resultado regiones con una alta probabilidad de densidad electrónica, mientras que las ondas fuera de fase producen nodos o regiones sin densidad electrónica.


 La combinación en fase de dos orbitales atómicos s en átomos adyacentes produce un orbital molecular de enlace σs de menor energía en el que la mayor parte de la densidad electrónica está directamente entre los núcleos. La adición fuera de fase produce un orbital molecular antienlazante σs* de mayor energía, en el que hay un nodo entre los núcleos.


 De manera similar, la función de onda de los orbitales p da lugar a dos lóbulos con fases opuestas. Cuando los orbitales p se superponen de un extremo a otro, crean orbitales σ y σ*. La superposición de dos orbitales p genera orbitales moleculares de enlace π y antienlazantes π*.


 El diagrama de orbitales moleculares lleno muestra el número de electrones en los orbitales moleculares enlazantes y antienlazantes. Un electrón contribuye a una interacción de enlace sólo si ocupa un orbital de enlace. La contribución neta de los electrones a la fuerza del enlace de una molécula se determina a partir del orden de enlace, que se calcula de la siguiente manera:

 <img alt="Figure1" src="/files/ftp_upload/11687/11687%20PT%20equation%201.png" style="text-align: center; height: 40px;">

 El orden de los enlaces es una guía para determinar la fuerza de un enlace covalente; un enlace entre dos átomos dados se vuelve más fuerte a medida que aumenta el orden del enlace. Si la distribución de electrones en los orbitales moleculares produce un enlace de orden cero, no se forma un enlace estable.


 La teoría de los orbitales moleculares también es útil para moléculas poliatómicas. El modelo de Lewis del benceno (C6H6), que tiene una estructura hexagonal plana con átomos de carbono con hibridación sp2, no puede representar con precisión sus electrones deslocalizados. Sin embargo, la teoría de los orbitales moleculares asigna esos electrones a tres orbitales moleculares de enlace π que cubren todo el anillo de carbono. Esto da como resultado un conjunto de orbitales moleculares de enlace completamente ocupados (6 electrones) que dotan al anillo de benceno de estabilidad termodinámica y química adicional.

Teoría MO y enlace covalente

La teoría de orbitales moleculares describe la distribución de electrones en moléculas de una manera similar a la distribución de electrones en orbitales atómicos. ...

Education

Educación

JoVE Core

Organic Chemistry

Química Orgánica

Unit 1

Unidad 1

Covalent Bonding and Structure

Enlace covalente y estructura

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

bond order and molecular orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found.

Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no electron density.

Two adjacent s orbitals can overlap to form a lower-energy sigma s bonding molecular orbital. In this orbital, most of the electron density lies between the nuclei. The out-of-phase combination forms a higher-energy sigma s* antibonding molecular orbital, which has a node between the nuclei.

p orbitals also build molecular orbitals. Their wave functions have two lobes with opposite phases. End-to-end overlap of p orbitals produces sigma and sigma* orbitals, while side-by-side overlap produces pi bonding and pi* antibonding molecular orbitals.

A filled molecular orbital diagram shows how many electrons occupy bonding and antibonding orbitals. An electron adds to bond strength only when it is in a bonding orbital. The overall effect is measured by bond order, which helps show how strong a covalent bond is.

As bond order increases, the bond between two atoms becomes stronger. If the molecular orbital arrangement gives a bond order of zero, a stable bond does not form. Molecular orbital theory also helps explain polyatomic molecules. In benzene, the Lewis model cannot show the delocalized electrons in its planar hexagonal ring of sp2 hybridized carbon atoms. Molecular orbital theory places those electrons in three pi bonding molecular orbitals spread across the whole ring. With 6 electrons filling these bonding orbitals, benzene gains extra thermodynamic and chemical stability.

Bond Order and Molecular Orbitals

what is organic chemistry?

Carbon Compounds in Everyday Life

Organic chemistry focuses on carbon compounds called organic compounds. These compounds may come from living things or be made by chemists. Carbon is the main element in them, and it bonds with other carbon atoms as well as hydrogen, oxygen, nitrogen, and sulfur. Carbon can form up to four strong bonds. That ability lets carbon atoms build chains and rings of many sizes, shapes, and levels of complexity. Not every carbon-containing substance is classified as organic. Carbonates, cyanides, and...

electronic structure of atoms

Atomic Orbitals and Quantum Numbers

Atomic orbitals and quantum numbers describe how electrons are arranged around the nucleus. An atom has a small, positively charged nucleus with electrons surrounding it. The nucleus contains protons and neutrons, and the quantum mechanical model gives a better picture of this structure than older models. Protons carry a +1 charge and have a mass of 1.0073 amu. Neutrons have no charge and have a mass of 1.0087 amu. Electrons carry a −1 charge and have a mass of 0.00055 amu. The number of...

electron configurations

How Electrons Fill Atomic Orbitals

Electron filling in atoms follows a set order based on orbital energy. The Aufbau principle says each new electron enters the lowest-energy subshell available. The Pauli exclusion principle says no two electrons can share the same set of four quantum numbers. Hund’s rule of maximum multiplicity says electrons stay unpaired in equal-energy orbitals when possible. The order of filling follows the relative energies of the subshells. A common sequence is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.

chemical bonds

Chemical Bonds: Types and Strength

Chemical bonds help atoms reach a full valence shell like the nearest noble gas. The main bond types are ionic, covalent, and metallic. Bond energy and bond length also help explain how strong a bond is. An ionic bond forms from electrostatic attraction between cations and anions. In many cases, one atom transfers electrons to another atom, and the ions form from that transfer. Ionic bonds have no defined direction because the attraction spreads evenly through three-dimensional space. A...

polar covalent bonds

Electronegativity in Polar Covalent Bonds

Polar covalent bonds form when atoms share electrons unevenly. This happens in covalent bonds between atoms that have similar, but not identical, tendencies to attract electrons. Nonmetal atoms often make these bonds with other nonmetals. Hydrogen gas, H2, is a simple example of a covalent bond between two hydrogen atoms. A covalent bond begins when two atoms move close enough for their valence orbitals to overlap. In hydrogen, the 1s orbitals overlap and the single electrons on each atom...

lewis structures and formal charges

Lewis Structures, Bonds, and Formal Charge

Lewis structures show how atoms share electrons in covalent bonds and in polyatomic ions. Lewis symbols help draw these structures, and the periodic table helps predict how many valence electrons an atom has and how many bonds it can form to reach an octet. Group 18 elements, such as argon and helium, already have filled electron configurations. They rarely take part in chemical bonding. Atoms in group 17, such as bromine and iodine, need one more electron to reach an octet, so they can form...

vsepr theory

Molecular Shapes from Electron Pairs

Molecular shape can be predicted from the way electron pairs arrange around a central atom. Valence shell electron-pair repulsion theory, or VSEPR theory, uses a Lewis structure to count bonding pairs and lone electron pairs. The main idea is simple: electron pairs spread out as far as possible to reduce repulsion. In a molecule, the valence electrons around the central atom can be bonding pairs or lone pairs. Bonding pairs are found mainly between bonded atoms. Lone pairs stay on one atom and...

molecular geometry and dipole moments

Predicting Shape and Molecular Polarity

Molecular shape and molecular polarity can be predicted with VSEPR theory and dipole moments. Start by writing the Lewis structure of the molecule or polyatomic ion. Then count the electron groups around the central atom. Lone pairs and bonds both count as electron groups, and a single, double, or triple bond each counts as one region of electron density. Use that count to identify the electron-pair geometry. Next, use the number of lone pairs to determine the molecular structure. If more than...

resonance and hybrid structures

Resonance in Nitrite and Carbonate Ions

Resonance explains why some Lewis structures do not match the measured properties of a molecule or ion. When two or more Lewis structures have the same atom arrangement, the real electron distribution is an average of the structures shown. The nitrite anion, NO2−, is one example. It can be drawn in two ways, with the N–O and N=O bonds in different places. If nitrite had one single bond and one double bond, the two bond lengths should be different, because a double bond is shorter and stronger...

valence bond theory and hybridized orbitals

valence-bond-theory-and-hybridized-orbitals

Covalent Bond Overlap and Orbital Hybridization

Covalent bonds form when orbitals on two atoms overlap and their single electrons pair up. The bond is stronger when the overlap is greater. Maximum overlap happens when the orbitals meet along a direct line between the two nuclei. A sigma bond, or σ bond, is the kind of covalent bond found in a single bond in a Lewis structure. In a σ bond, electron density is concentrated along the internuclear axis. A pi bond, or π bond, forms when two p orbitals overlap side by side. In a π bond, the...

mo theory and covalent bonding

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found. Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no...

intermolecular forces and physical properties

intermolecular-forces-and-physical-properties

How Intermolecular Forces Affect Matter

Intermolecular forces are the attractions between molecules, and they help explain how matter behaves. These forces influence melting points, boiling points, and whether substances mix with one another. Water has a much higher boiling point than hexane, which shows that water has stronger intermolecular forces. Three main kinds of intermolecular interactions are covered here. They include ion-dipole forces, dipole-dipole interactions, and van der Waals forces, which include London dispersion...

solubility

Why Some Substances Dissolve in Water

Solution formation depends on how solutes and solvents interact. A solution is a homogeneous mixture made of a solvent, which is the larger part, and a solute, which is the smaller part. The physical state of a solution is usually the same as the solvent. Concentration is often described as dilute for a low amount of solute or concentrated for a high amount of solute. When a solute dissolves, its particles are surrounded by solvent species. This process is called solvation. If water is the...

introduction to functional groups

Functional Groups and Organic Molecules

Functional groups are groups of atoms with specific chemical properties that appear within organic molecules. They are sometimes shown as "R." These groups sit along the carbon backbone of macromolecules, which can form chains or rings of carbon atoms. Functional groups help functionalize a compound. That means they can give the molecule different physical and chemical properties. In organic chemistry, this change in group structure can strongly affect how a compound behaves. Common...

overview of advanced functional groups

Advanced Functional Groups in Organic Chemistry

Advanced functional groups are atom clusters in organic molecules that give those molecules specific chemical properties. They are sometimes shown as "R" in formulas. By changing the atoms attached to a carbon skeleton, a functional group can make a compound behave differently in physical and chemical reactions. This topic covers several major classes of organic compounds with advanced functional groups. Aromatic hydrocarbons include benzene. Phenol is another example and is also called...

key terms and concepts

Learn how molecular orbitals form from atomic orbitals, how bond order predicts bond strength, and why benzene is unusually stable in MO theory.

Bond Order and Molecular Orbitals | JoVE K12

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9C.3.2.1.3

4 Communicating reasons, arguments and ideas to others
 4.2 Obtaining, evaluating and communicating information
  4.2.1 Students will be able to read and interpret multiple sources to obtain information, evaluate the merit and validity of claims and design solutions, and communicate information, ideas, and evidence in a variety of formats.

Bond Order and Molecular Orbitals

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