8.3 Multiple Bonds
3 min read•june 25, 2024
Covalent bonds form when atoms share electrons, creating molecules with unique properties. These bonds involve , resulting in single, double, or triple bonds that determine molecular shape and reactivity.
Resonance and play crucial roles in molecular stability. Understanding sigma and pi bonds helps explain bond strengths and molecular geometries, while provides a deeper insight into bonding mechanisms and electronic structures.
Covalent Bonding and Molecular Structure
Atomic orbital overlap in bonding
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- Covalent bonds form when atomic orbitals overlap and share electrons
- Single bonds form from overlap of two atomic orbitals, one from each bonding atom (H)
- Double and triple bonds form from overlap of additional atomic orbitals (CH, CH)
- Sigma () bonds form by direct, end-to-end overlap of atomic orbitals along internuclear axis
- All single bonds are bonds (H, CH)
- One bond is present in double and triple bonds (CH, CH)
- Pi () bonds form by parallel overlap of p orbitals above and below internuclear axis
- Double bonds contain one and one bond (CH)
- Triple bonds contain one and two bonds (CH)
- mixes atomic orbitals to form new hybrid orbitals with specific geometries
- results in and can form triple bonds (CH)
- sp hybridization results in and can form double bonds (CH)
- sp hybridization results in and can form single bonds (CH)
Resonance and electron delocalization
- Resonance occurs when a molecule can be represented by multiple valid Lewis structures
- Resonance structures are hypothetical and do not exist independently (, CH)
- Actual structure is a hybrid of all resonance structures (benzene, CH)
- Electron delocalization spreads over multiple atoms in a molecule
- Occurs when there are multiple equivalent resonance structures (benzene, CH)
- Results in a more stable molecule with lower energy than any individual resonance structure (, COO)
- measures stability gained through electron delocalization
- Difference in energy between actual molecule and most stable resonance structure (benzene, CH)
Sigma vs pi bonds
- Sigma () bonds are stronger than bonds due to greater orbital overlap
- Formed by direct, end-to-end overlap of atomic orbitals (H, CH)
- Electron density is concentrated along internuclear axis
- Rotation around bonds is possible
- Pi () bonds are weaker than bonds due to less orbital overlap
- Formed by parallel overlap of p orbitals above and below internuclear axis (CH, CH)
- Electron density is concentrated above and below internuclear axis
- Rotation around bonds is restricted, resulting in planar geometry
- Bond lengths
- Multiple bonds are shorter than single bonds due to increased electron density between nuclei
- Triple bonds are shorter than double bonds, which are shorter than single bonds (CH < CH < CH)
- Bond strengths
- Multiple bonds are stronger than single bonds due to increased electron sharing
- Triple bonds are stronger than double bonds, which are stronger than single bonds (CH > CH > CH)
- increases with , reflecting the strength of multiple bonds
Molecular Orbital Theory
- Describes bonding in terms of molecular orbitals formed from linear combinations of atomic orbitals
- Bonding orbitals result in lower energy and increased electron density between nuclei
- result in higher energy and decreased electron density between nuclei
- is calculated as (bonding electrons - antibonding electrons) / 2, indicating bond strength and length
Key Terms to Review (36)
Acetylene: Acetylene is a colorless, flammable gas with the chemical formula C₂H₂. It is the simplest alkyne and is widely used in various industrial and chemical applications, particularly in the context of multiple bonds in organic chemistry.
Antibonding Orbitals: Antibonding orbitals are a type of molecular orbital that have a higher energy state compared to the bonding orbitals. They are formed when the constructive interference of atomic orbitals results in a region of decreased electron density between the bonded atoms, leading to a destabilization of the molecular system.
Atomic Orbital Overlap: Atomic orbital overlap refers to the interaction and sharing of electron density between two or more atomic orbitals, which is a crucial factor in the formation of chemical bonds. This concept is particularly important in the context of understanding multiple bonds between atoms.
Benzene: Benzene is a colorless, flammable, and aromatic hydrocarbon compound with the chemical formula C₆H₆. It is a key component in the study of multiple bonds, particularly in the context of organic chemistry and the structure of aromatic compounds.
Bond Dissociation Energy: Bond dissociation energy is the amount of energy required to break a specific chemical bond between two atoms, separating them into individual, free atoms. This term is crucial in understanding the strengths of ionic and covalent bonds, as well as the formation of multiple bonds between atoms.
Bond order: Bond order is the number of chemical bonds between a pair of atoms. It indicates the stability and strength of a bond.
Bond Order: Bond order is a concept that describes the strength and stability of a chemical bond between atoms. It is a measure of the number of shared electron pairs between two atoms, and it plays a crucial role in understanding the properties and reactivity of molecules.
Carbon: Carbon is a fundamental element that is essential for the formation of organic compounds and the sustenance of life. It is a versatile element that can form a wide range of structures and participate in numerous chemical reactions, making it a crucial component in various fields, including chemistry, biology, and materials science.
Carboxylate Ion: The carboxylate ion is a negatively charged functional group composed of a carbon atom double-bonded to an oxygen atom and singly-bonded to another oxygen atom, which carries a negative charge. It is an important species in many organic and biochemical processes.
Covalent Bonding: Covalent bonding is a type of chemical bond that involves the sharing of one or more pairs of electrons between atoms. This type of bond is responsible for the formation of many stable molecules and is a fundamental concept in understanding the structure and properties of various substances, including those covered in the topics of 8.3 Multiple Bonds, 18.1 Periodicity, 18.3 Structure and General Properties of the Metalloids, 18.5 Occurrence, Preparation, and Compounds of Hydrogen, and 18.7 Occurrence, Preparation, and Properties of Nitrogen.
Double bond: A double bond is a type of covalent bond in which two pairs of electrons are shared between two atoms. Double bonds are commonly found in organic molecules and influence molecular geometry and reactivity.
Double Bond: A double bond is a covalent bond in which two pairs of electrons are shared between two atoms, resulting in a stronger and more stable bond compared to a single bond. This type of bond is commonly observed in organic chemistry and plays a crucial role in the structure and reactivity of many chemical compounds.
Electron delocalization: Electron delocalization refers to the phenomenon where electrons are not confined to a specific bond or atom but are spread out over several atoms, allowing for a more stable arrangement. This concept is crucial in understanding how molecules can have multiple resonance structures, which reflect the shifting nature of electron distribution and enhance stability in certain compounds, especially those with multiple bonds and complex bonding scenarios.
Electron Density: Electron density is a fundamental concept in quantum mechanics that describes the probability distribution of electrons within an atom or molecule. It is a crucial factor in understanding the behavior and properties of chemical systems.
Ethene: Ethene, also known as ethylene, is a simple unsaturated hydrocarbon with the molecular formula C2H4. It is a colorless, flammable gas that is widely used in the chemical industry and is a key intermediate in the production of many organic compounds.
Hybridization: Hybridization is the concept in chemistry where atomic orbitals combine to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. This idea helps explain molecular geometry and bonding properties, linking the arrangement of atoms in a molecule to their electron configurations and the types of bonds formed.
Hydrogen: Hydrogen is the simplest and lightest element in the periodic table, with a single proton and electron in its neutral state. It is a highly reactive nonmetal that plays a crucial role in various chemical processes and is a fundamental component of many compounds, making it a key topic across several areas of chemistry.
Hydrogen bonding: Hydrogen bonding is a strong type of dipole-dipole interaction that occurs between molecules when hydrogen is covalently bonded to electronegative atoms like oxygen, nitrogen, or fluorine. This bond results in higher boiling and melting points for substances.
Linear Geometry: Linear geometry refers to the spatial arrangement of atoms or groups in a molecule where the bonds between the central atom and the surrounding atoms form a straight line. This geometric configuration is a key characteristic of certain molecular structures.
Methane: Methane is a colorless, odorless gas with the chemical formula CH₄, primarily composed of carbon and hydrogen. It is the simplest alkane and serves as a primary component of natural gas, making it an important fuel source and a significant greenhouse gas contributing to climate change.
Molecular orbital theory: Molecular orbital theory is a method used to describe the electronic structure of molecules by combining atomic orbitals to form molecular orbitals that are spread over multiple atoms. This theory explains how electrons are shared between atoms, leading to bonding and anti-bonding interactions that dictate the stability and properties of molecules. Understanding this concept is crucial when examining the behavior of electrons in resonance structures, hybridization, and the formation of multiple bonds.
Nitrogen: Nitrogen is a chemical element with the atomic number 7 and the symbol N. It is a colorless, odorless, and tasteless gas that makes up approximately 78% of the Earth's atmosphere. Nitrogen is an essential element for life, playing crucial roles in various chemical and biological processes.
Nitrogen fixation: Nitrogen fixation is the process by which molecular nitrogen ($N_2$) in the atmosphere is converted into ammonia ($NH_3$) or related nitrogenous compounds in soil. This process is essential for making nitrogen available to living organisms.
Oxygen: Oxygen is a highly reactive nonmetallic element that is essential for most forms of life. It is the third most abundant element in the universe and the most abundant element on Earth's crust. Oxygen plays a crucial role in various chemical and biological processes, including respiration, combustion, and oxidation-reduction reactions.
Pi bond: A pi bond is a type of covalent bond formed when two atomic orbitals overlap laterally, resulting in an electron density that is concentrated above and below the internuclear axis. This bond occurs alongside a sigma bond in double or triple bonds, and plays a critical role in the structure and reactivity of molecules by influencing their geometry and electronic properties.
Resonance Energy: Resonance energy is the stabilizing energy that arises from the delocalization of electrons in a molecule, particularly in aromatic compounds. It is the difference in energy between the actual molecule and a hypothetical molecule with localized bonds, and it contributes to the stability and reactivity of the compound.
Sigma Bond: A sigma bond is a type of covalent chemical bond formed by the head-on overlap of atomic orbitals, resulting in a high electron density concentrated along the internuclear axis between two bonded atoms. This type of bond is the strongest and most common type of covalent bond, and it plays a crucial role in the stability and structure of molecules.
Sigma bonds (σ bonds): Sigma bonds (σ bonds) are covalent bonds formed by the head-on overlap of atomic orbitals. They allow for free rotation around the bond axis.
Single Bond: A single bond is a covalent chemical bond in which two atoms share a single pair of electrons. It is the simplest and most common type of chemical bond, forming a stable connection between atoms.
Sp Hybridization: sp Hybridization is a type of atomic orbital hybridization where an atom's s orbital and one of its p orbitals combine to form two equivalent hybrid orbitals. This hybridization occurs in molecules with linear geometry, such as carbon dioxide and acetylene, and is crucial in understanding the formation of multiple bonds between atoms.
Sp² Hybridization: sp² hybridization is a type of orbital hybridization that occurs in carbon atoms and other elements, where one s orbital and two p orbitals combine to form three equivalent sp² hybrid orbitals. This hybridization is crucial in understanding the structure and bonding of many organic compounds, especially those with multiple bonds.
Sp³ Hybridization: sp³ hybridization is a type of atomic orbital hybridization that occurs when an atom's s orbital and three p orbitals combine to form four equivalent hybrid orbitals. This hybridization is commonly observed in carbon compounds with four single bonds, such as methane (CH₄).
Tetrahedral Geometry: Tetrahedral geometry refers to the three-dimensional arrangement of atoms or groups of atoms in a molecular structure, where the central atom is bonded to four other atoms or groups in a tetrahedral configuration. This specific geometric arrangement is a key concept in understanding the behavior and properties of multiple bonds in chemistry.
Trigonal Planar Geometry: Trigonal planar geometry is a molecular geometry in which a central atom is covalently bonded to three other atoms, resulting in a flat, triangular arrangement around the central atom. This geometry is commonly observed in molecules with multiple bonds, such as those described in the context of Section 8.3: Multiple Bonds.
Triple bond: A triple bond is a type of chemical bond where three pairs of electrons are shared between two atoms. It is typically found in molecules like nitrogen (N₂) and acetylene (C₂H₂).
Triple Bond: A triple bond is a covalent bond in which three pairs of electrons are shared between two atoms, resulting in a very strong and stable chemical connection. This type of bond is found in various chemical structures and plays a crucial role in understanding valence bond theory, multiple bonds, and the properties of nitrogen.