6.3 Hybridization and molecular geometry
3 min read•august 7, 2024
Hybridization blends atomic orbitals, shaping molecules and influencing bonding. It's key to understanding how atoms connect and form specific structures. This concept ties into molecular orbital theory by explaining electron behavior in chemical bonds.
predicts molecular shapes based on electron pair repulsion. It's crucial for grasping 3D molecular structures and their properties. This links to electronic structure by showing how electron arrangement affects molecular geometry.
Hybridization and Bonding
Hybrid Orbitals and Bond Types
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- Hybridization involves the mixing of atomic orbitals to form new hybrid orbitals with specific shapes and orientations
- hybridization occurs when one s and one p orbital combine to form two sp hybrid orbitals arranged in a geometry (180° bond angle)
- sp2 hybridization occurs when one s and two p orbitals combine to form three sp2 hybrid orbitals arranged in a geometry (120° )
- sp3 hybridization occurs when one s and three p orbitals combine to form four sp3 hybrid orbitals arranged in a geometry (109.5° bond angles)
- Sigma (σ) bonds are formed by the direct overlap of atomic orbitals along the internuclear axis resulting in a single covalent bond (C-C single bond)
- Pi (π) bonds are formed by the sideways overlap of unhybridized p orbitals resulting in a weaker secondary covalent bond (C=C double bond)
Valence Bond Theory
- describes the formation of covalent bonds through the overlap of atomic orbitals
- Hybrid orbitals are used to explain the observed molecular geometries and bond angles in molecules
- The number of hybrid orbitals formed is equal to the number of atomic orbitals that participate in the hybridization process
- Hybrid orbitals are oriented in space to minimize electron repulsion and maximize bond stability
- The type of hybridization (sp, sp2, or sp3) determines the shape and bond angles of the molecule (linear, trigonal planar, or tetrahedral)
- Valence bond theory provides a qualitative understanding of chemical bonding but does not account for the delocalization of electrons in molecules
Molecular Geometry
VSEPR Theory and Molecular Shapes
- VSEPR (Valence Shell Electron Pair Repulsion) theory predicts the geometry of molecules based on the repulsion between electron pairs
- Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule determined by the number and type of electron pairs (bonding and nonbonding) around the central atom
- Electron pairs (bonding and nonbonding) repel each other and arrange themselves to minimize repulsion leading to specific molecular geometries (linear, trigonal planar, tetrahedral, , or )
- Lone pairs of electrons occupy more space than bonding pairs resulting in slightly distorted geometries (, trigonal pyramidal, or seesaw) compared to the ideal geometries predicted by VSEPR theory
Bond Angles and Molecular Polarity
- Bond angles are the angles formed between the imaginary lines connecting the nuclei of the bonded atoms in a molecule
- The ideal bond angles for common geometries are 180° (linear), 120° (trigonal planar), 109.5° (tetrahedral), 90° and 120° (trigonal bipyramidal), and 90° (octahedral)
- The presence of lone pairs causes a slight decrease in bond angles due to their greater repulsive effect compared to bonding pairs (H2O bond angle is 104.5° instead of the ideal 109.5° for a tetrahedral arrangement)
- Molecular polarity depends on the geometry of the molecule and the polarity of individual bonds ( have an uneven distribution of charge, while have a balanced distribution of charge)
- Molecules with symmetric geometries and no lone pairs are typically nonpolar (CO2 is linear and nonpolar), while molecules with asymmetric geometries or lone pairs are typically polar (NH3 is trigonal pyramidal and polar)
Key Terms to Review (21)
Bent: In molecular geometry, 'bent' refers to a molecular shape where three atoms form an angle, typically due to the presence of lone pairs on the central atom. This geometry results in a non-linear arrangement, affecting the molecule's polarity and reactivity. The bent shape often occurs in molecules with a central atom that is bonded to two other atoms and has one or more lone pairs, influencing both physical and chemical properties.
Bond angles: Bond angles are the geometric angles between adjacent bonds in a molecule, measured at the atom that is bonded to two other atoms. These angles play a crucial role in determining the three-dimensional shape of a molecule, which in turn influences its reactivity and interactions with other molecules. Understanding bond angles helps to explain how hybridization alters molecular geometry and affects the overall properties of a substance.
Ethene: Ethene, also known as ethylene, is a colorless gas with the formula C₂H₄, which is the simplest alkene. It consists of two carbon atoms connected by a double bond, along with four hydrogen atoms. This unique structure contributes to its reactivity and makes it an important building block in organic chemistry and various industrial processes.
Linear: In chemistry, 'linear' refers to a specific molecular geometry where atoms are arranged in a straight line, typically with bond angles of 180 degrees. This configuration arises from the hybridization of atomic orbitals, particularly in molecules with two bonding pairs and no lone pairs. Linear shapes are commonly observed in diatomic molecules and certain polyatomic compounds, showcasing how geometry influences molecular properties.
Linus Pauling: Linus Pauling was an influential American chemist, biochemist, and peace activist known for his groundbreaking work in the fields of quantum chemistry and molecular biology. His contributions to the understanding of hybridization and molecular geometry significantly advanced the knowledge of chemical bonding and molecular structure.
Methane: Methane is a colorless, odorless gas with the chemical formula CH₄, and it is the simplest alkane and a major component of natural gas. In the context of hybridization and molecular geometry, methane serves as a classic example of sp³ hybridization, where one s orbital and three p orbitals from carbon combine to form four equivalent hybrid orbitals. This leads to a tetrahedral molecular geometry with bond angles of approximately 109.5 degrees, illustrating the principles of molecular shape and bonding.
Nonpolar molecules: Nonpolar molecules are chemical species that have an equal distribution of electrical charge, resulting in no permanent dipoles. These molecules typically consist of atoms with similar electronegativities, which leads to a balanced sharing of electrons and a lack of significant charge separation. Nonpolar molecules often exhibit specific behaviors in hybridization and molecular geometry, impacting their physical properties and interactions with other substances.
Octahedral: Octahedral refers to a molecular geometry where a central atom is surrounded by six other atoms or groups of atoms, arranged at the vertices of an octahedron. This geometry arises from the hybridization of orbitals and is characterized by bond angles of 90 degrees and 180 degrees, reflecting the symmetrical arrangement of atoms around the central atom.
Pi bonds: Pi bonds are a type of covalent bond that occurs when two atomic orbitals overlap laterally, resulting in the sharing of electrons above and below the bond axis. These bonds typically form in conjunction with sigma bonds, allowing for the creation of double or triple bonds between atoms. In terms of molecular geometry, pi bonds play a crucial role in determining the shape and reactivity of molecules, especially in organic compounds.
Polar molecules: Polar molecules are molecules that have a partial positive charge on one end and a partial negative charge on the other due to uneven distribution of electron density. This polarity arises from the differences in electronegativity between atoms, leading to dipole moments that affect molecular interactions, geometry, and properties like solubility and boiling points.
Robert S. Mulliken: Robert S. Mulliken was an influential American theoretical chemist who made significant contributions to molecular orbital theory and the understanding of hybridization. His work laid the foundation for the modern interpretation of how atomic orbitals combine to form molecular orbitals, and he developed methods that are crucial for predicting molecular geometries and electron distributions in conjugated systems.
Sigma bonds: Sigma bonds are a type of covalent bond formed when two atomic orbitals overlap head-on, allowing for the sharing of electron density along the axis connecting the two nuclei. This bond is characterized by its cylindrical symmetry around the bond axis, making it the strongest type of covalent bond. Sigma bonds are fundamental in determining molecular geometry as they provide the framework for how atoms connect and arrange themselves in three-dimensional space.
Sp: The 'sp' hybridization refers to a specific type of atomic orbital hybridization that involves the mixing of one s orbital and one p orbital from the same atom to form two equivalent sp hybrid orbitals. This hybridization is significant because it leads to linear molecular geometries, which can explain the bonding patterns seen in molecules like acetylene (C2H2) and carbon dioxide (CO2). The sp hybridization affects bond angles, molecular shape, and overall reactivity of compounds, illustrating the connection between electronic structure and molecular geometry.
Sp²: sp² hybridization refers to a type of hybrid orbitals formed when one s orbital and two p orbitals combine to create three equivalent orbitals. These hybrid orbitals are arranged in a trigonal planar geometry, with bond angles of approximately 120 degrees, which is crucial in determining the shape and bonding properties of molecules.
Sp³: sp³ refers to a specific type of hybridization that occurs when one s orbital and three p orbitals combine to form four equivalent sp³ hybrid orbitals. This hybridization is crucial in determining the geometry and bonding properties of molecules, leading to a tetrahedral molecular shape with bond angles of approximately 109.5 degrees. The concept of sp³ hybridization plays a vital role in understanding the three-dimensional arrangement of atoms in various organic and inorganic compounds.
Tetrahedral: Tetrahedral refers to a molecular geometry where a central atom is surrounded by four other atoms positioned at the corners of a tetrahedron. This arrangement results from sp³ hybridization, where one s orbital and three p orbitals mix to form four equivalent hybrid orbitals. The tetrahedral shape minimizes repulsion between the bonding pairs of electrons, leading to a stable molecular structure.
Trigonal bipyramidal: Trigonal bipyramidal refers to a molecular geometry where a central atom is surrounded by five other atoms or groups of atoms, arranged in a specific three-dimensional shape. This geometry features two distinct types of bond angles: 90° between the axial and equatorial positions, and 120° between the equatorial atoms, creating a unique spatial arrangement that plays a significant role in determining the properties of the molecule.
Trigonal planar: Trigonal planar refers to a molecular geometry where a central atom is surrounded by three other atoms, positioned at the corners of an equilateral triangle, all in the same plane. This arrangement typically occurs when the central atom has three bonding pairs and no lone pairs of electrons, leading to bond angles of approximately 120 degrees. This geometry is often seen in molecules with sp ext{ } hybridization, where the central atom uses three hybrid orbitals for bonding.
Valence Bond Theory: Valence Bond Theory (VBT) is a fundamental concept in chemistry that describes how atomic orbitals combine to form chemical bonds. The theory emphasizes the role of overlapping atomic orbitals and the pairing of electrons with opposite spins, which leads to bond formation. This approach helps to explain the geometric arrangement of atoms in a molecule through hybridization, linking it to molecular shapes and reactivity.
VSEPR Theory: VSEPR Theory, or Valence Shell Electron Pair Repulsion Theory, is a model used to predict the three-dimensional shape of molecules based on the repulsion between electron pairs surrounding a central atom. It emphasizes that electron pairs, both bonding and lone pairs, will arrange themselves in a way that minimizes repulsion, resulting in specific molecular geometries. This theory is crucial in understanding how hybridization leads to different molecular shapes and bond angles.
Water: Water is a simple molecule consisting of two hydrogen atoms covalently bonded to one oxygen atom, forming the chemical formula H₂O. Its unique properties, such as being a polar molecule and exhibiting hydrogen bonding, significantly influence molecular geometry and hybridization in various compounds and reactions.