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Organic Chemistry
Table of Contents
Unit 1 Overview: Structure and Bonding
1.1 Atomic Structure: The Nucleus
1.2 Atomic Structure: Orbitals
1.3 Atomic Structure: Electron Configurations
1.4 Development of Chemical Bonding Theory
1.5 Describing Chemical Bonds: Valence Bond Theory
1.6 sp3 Hybrid Orbitals and the Structure of Methane
1.7 sp3 Hybrid Orbitals and the Structure of Ethane
1.8 sp2 Hybrid Orbitals and the Structure of Ethylene
1.9 sp Hybrid Orbitals and the Structure of Acetylene
1.10 Hybridization of Nitrogen, Oxygen, Phosphorus, and Sulfur
1.11 Describing Chemical Bonds: Molecular Orbital Theory
1.12 Drawing Chemical Structures

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1.7 sp3 Hybrid Orbitals and the Structure of Ethane

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Ethane's structure showcases the beauty of carbon bonding. Two methyl groups join hands through a single C-C bond, with each carbon sporting a tetrahedral arrangement of sp3 hybrid orbitals. This setup allows for strong, directional covalent bonds and that iconic 109.5° angle.

Diving into the bonds, we see C-H connections outshining their C-C counterparts. These shorter, stronger links result from hydrogen's small size and the electronegativity difference. Meanwhile, the C-C bond's symmetry enables free rotation, a key feature in ethane's flexibility.

Structure and Bonding in Ethane

Structure of ethane molecule

  • Ethane ($CH_3CH_3$) composed of two methyl groups joined by a single C-C bond
  • Each carbon atom undergoes sp3 hybridization combines one 2s and three 2p orbitals forming four equivalent sp3 hybrid orbitals
  • sp3 hybrid orbitals arrange in a tetrahedral geometry surrounding each carbon atom minimizing electron repulsion and maximizing stability
  • C-C bond formed by overlap of one sp3 hybrid orbital from each carbon atom creates a sigma ($\sigma$) bond (single bond)
  • Remaining three sp3 hybrid orbitals on each carbon atom overlap with 1s orbitals of hydrogen atoms forming C-H sigma ($\sigma$) bonds
  • Bond angles in ethane approximately 109.5° result from tetrahedral arrangement of sp3 hybrid orbitals around each carbon atom (tetrahedral geometry)

Carbon-carbon bonding with sp3 orbitals

  • In ethane and saturated hydrocarbons carbon atoms form single bonds using sp3 hybrid orbitals
  • sp3 hybridization process mixes one 2s and three 2p atomic orbitals creating four equivalent sp3 hybrid orbitals
  • sp3 hybrid orbitals orient in a tetrahedral arrangement minimizing electron repulsion and maximizing stability (staggered conformation)
  • C-C bond forms through end-on overlap of one sp3 hybrid orbital from each carbon atom creates a sigma ($\sigma$) bond (strong covalent bond)
  • Remaining sp3 hybrid orbitals on each carbon atom can form additional single bonds with other atoms (hydrogen, carbon)
  • Orbital overlap between sp3 hybrid orbitals results in strong, directional covalent bonds

C-H vs C-C bonds in ethane

  • In ethane C-H and C-C bonds are sigma ($\sigma$) bonds formed by overlap of atomic orbitals
  • C-H bonds:
    • Formed by overlap of sp3 hybrid orbital from carbon and 1s orbital from hydrogen
    • Bond length approximately 1.09 Å (angstroms) shorter than C-C bond
    • Bond energy approximately 99 kcal/mol stronger than C-C bond
  • C-C bond:
    • Formed by overlap of two sp3 hybrid orbitals one from each carbon atom
    • Bond length approximately 1.54 Å (angstroms) longer than C-H bond
    • Bond energy approximately 83 kcal/mol weaker than C-H bond
  • C-H bond shorter and stronger than C-C bond due to:
    • Smaller size of hydrogen atom compared to carbon atom leads to shorter bond length
    • Greater electronegativity difference between carbon and hydrogen leads to more polar and stronger bond (dipole moment)

Hybridization and Bonding in Ethane

  • Electron configuration of carbon (1s² 2s² 2p²) undergoes hybridization to form sp3 hybrid orbitals
  • Hybridization results in four equivalent sp3 hybrid orbitals used in bonding
  • Bond rotation around the C-C single bond in ethane is possible due to the symmetrical nature of the sigma (σ) bond

Key Terms to Review (33)

Urethane: Urethane, also known as ethyl carbamate, is a compound formed from the reaction between an alcohol and an isocyanate group as part of the step-growth polymerization process. It is a key building block in the production of polyurethanes, which are versatile synthetic polymers used in a wide range of applications from foams to elastomers.
Staggered conformation: In organic chemistry, staggered conformation is a specific spatial arrangement of atoms in ethane and similar molecules where the hydrogen atoms attached to adjacent carbon atoms are as far apart as possible, minimizing repulsion between electron clouds. This arrangement results in a more stable, lower energy state for the molecule.
Sp3 hybrid orbitals: sp3 hybrid orbitals are formed by the combination of one s orbital and three p orbitals in an atom, resulting in four equivalent orbitals oriented tetrahedrally around the central atom. This hybridization occurs in atoms that form four covalent bonds, such as carbon in methane (CH4).
Dipole moment (𝜇): A dipole moment is a measure of the separation of positive and negative electrical charges within a molecule, indicating the polarity of a bond or molecule. It is quantitatively expressed in units of Debye (D) and results from differences in electronegativity between bonded atoms.
Electron configuration: Electron configuration describes the distribution of electrons in an atom's atomic orbitals. It follows a set of rules, including the Pauli exclusion principle and Hund's rule, to show how these electrons are arranged around the nucleus.
Bond angle: The bond angle is the geometric angle between two adjacent bonds originating from the same atom. In the context of sp3 hybrid orbitals and the structure of methane, it refers to the angle between any two covalent bonds that join atoms to the central carbon atom.
Bond length: Bond length is the average distance between the nuclei of two bonded atoms in a molecule. It determines the stability and strength of the bond, varying with bond order and atom size.
Electron Configuration: Electron configuration refers to the arrangement of electrons in an atom's orbitals, which determines the atom's chemical properties and behavior. This concept is central to understanding the structure and behavior of atoms, as well as the formation of chemical bonds and the properties of molecules.
Atomic Orbitals: Atomic orbitals are the wave-like functions that describe the behavior and spatial distribution of an electron in an atom. They are the fundamental building blocks of atomic structure and play a crucial role in understanding chemical bonding and reactivity.
VSEPR Theory: VSEPR (Valence Shell Electron Pair Repulsion) theory is a model used to predict the geometry of molecules based on the arrangement of electron pairs around a central atom. It explains how the placement of bonding and non-bonding electron pairs determines the shape of a molecule, which is crucial for understanding its chemical properties and reactivity.
Bond Length: Bond length refers to the distance between the nuclei of two bonded atoms in a molecule. It is a crucial parameter in understanding the structure and stability of chemical bonds, as it directly influences the strength and properties of the bond.
Hybridization: Hybridization is a fundamental concept in chemistry that describes the process of mixing atomic orbitals to form new hybrid orbitals, which are used to explain the geometry and bonding patterns of molecules. This term is closely related to the development of chemical bonding theory, valence bond theory, and molecular orbital theory, as well as the structure and properties of various organic compounds.
Saturated Hydrocarbons: Saturated hydrocarbons are a class of organic compounds consisting solely of carbon and hydrogen atoms, where all the carbon-carbon bonds are single bonds. They have the general formula C$_n$H$_{2n+2}$ and are characterized by the presence of only sp$^3$ hybridized carbon atoms, resulting in a tetrahedral geometry around each carbon.
109.5°: The angle of 109.5° is the bond angle between the four sp³ hybridized orbitals in a methane (CH₄) molecule, as well as the bond angle between the six sp³ hybridized orbitals in an ethane (C₂H₆) molecule. This bond angle is a key structural feature that arises from the tetrahedral arrangement of the hybridized orbitals.
Dipole Moment: Dipole moment is a measure of the separation of electric charge within a molecule or chemical bond. It represents the magnitude and direction of the unequal distribution of positive and negative charges, which can influence the behavior and properties of a molecule.
Sp3 Hybridization: sp3 hybridization refers to the formation of four equivalent hybrid orbitals in an atom, typically observed in carbon compounds. These hybridized orbitals are essential in understanding the structure and bonding patterns of various organic molecules, including alkanes, alkyl halides, and molecules containing nitrogen, oxygen, phosphorus, and sulfur.
Tetrahedral Geometry: Tetrahedral geometry refers to the three-dimensional spatial arrangement of atoms or groups of atoms in a molecule, where the central atom is bonded to four other atoms or groups in a symmetrical tetrahedral configuration. This geometric structure is a fundamental concept in understanding the structure and properties of various organic and inorganic compounds.
Sigma Bond: A sigma bond is a type of covalent chemical bond formed by the overlap of atomic orbitals along the internuclear axis between two atoms. Sigma bonds are the strongest type of covalent bonds and are responsible for the structural stability and geometry of molecules.
Alkane: Alkanes are a class of saturated hydrocarbons composed entirely of single-bonded carbon and hydrogen atoms. They are the simplest organic compounds and form the basis for many other organic molecules and reactions.
Bond Angle: The bond angle refers to the angle formed between the covalent bonds of a molecule. It is a crucial parameter that determines the three-dimensional structure and geometry of molecules, which in turn influences their physical and chemical properties.
Bond Rotation: Bond rotation refers to the ability of atoms in a molecule to rotate around a single covalent bond, allowing the molecule to adopt different spatial arrangements or conformations. This term is particularly relevant in the context of understanding the structure and behavior of alkanes, such as ethane, as well as the concept of sp3 hybridization.
Single Bond: A single bond is a covalent chemical bond where two atoms share a single pair of electrons. It is the simplest and most common type of covalent bond, and it is an essential structural feature in the context of sp3 hybrid orbitals and the structure of ethane.
Molecular Orbitals: Molecular orbitals are the wave functions that describe the behavior of electrons in a molecule. They are formed by the combination of atomic orbitals and play a crucial role in understanding the structure, bonding, and reactivity of chemical compounds.
Angstroms: An angstrom (Å) is a unit of length used to measure the size of atoms, molecules, and other small-scale structures. It is a fundamental unit in the description of chemical bonds and molecular geometry.
Ethane: Ethane is the simplest alkane, a saturated hydrocarbon with the chemical formula C2H6. It is a key term in understanding the concepts of sp3 hybrid orbitals, the structure of alkanes, and their properties.
Covalent Bond: A covalent bond is a chemical bond formed by the sharing of one or more pairs of electrons between two atoms. This type of bond is the fundamental basis for the stability and structure of many molecules, including those found in the topics of 1.5 Describing Chemical Bonds: Valence Bond Theory, 1.6 sp3 Hybrid Orbitals and the Structure of Methane, and 1.7 sp3 Hybrid Orbitals and the Structure of Ethane.
Bond Energy: Bond energy, also known as bond dissociation energy, refers to the amount of energy required to break a chemical bond between two atoms. It is a measure of the strength of the bond and plays a crucial role in understanding the stability and reactivity of molecules.
Sp3 Hybrid Orbitals: sp3 hybrid orbitals are a type of atomic orbital that arise when an atom, such as carbon, undergoes hybridization. This hybridization process combines one s orbital and three p orbitals to form four equivalent sp3 hybrid orbitals, which are essential in understanding the structure and bonding of many organic molecules.
Methyl Group: The methyl group (CH3-) is a functional group in organic chemistry composed of a single carbon atom bonded to three hydrogen atoms. It is a commonly occurring substituent in many organic compounds and plays a crucial role in the structure and properties of various molecules.
C-H Bond: The C-H bond is a covalent bond formed between a carbon atom and a hydrogen atom. This bond is fundamental to organic chemistry and is present in a wide range of organic compounds, from simple alkanes to complex biomolecules. The C-H bond is crucial in understanding the structure, reactivity, and stability of organic molecules.
Orbital Overlap: Orbital overlap refers to the interaction and sharing of electron density between two or more atomic orbitals, which is a fundamental concept in understanding the formation of chemical bonds. This term is particularly relevant in the context of valence bond theory, sp3 hybrid orbitals, and sp hybrid orbitals.
Carbon-Carbon Bond: A carbon-carbon bond is a covalent chemical bond that forms between two carbon atoms, connecting them together in organic molecules. This type of bond is fundamental to the structure and function of many organic compounds, including those found in living organisms.
Staggered Conformation: The staggered conformation is a three-dimensional arrangement of atoms in a molecule where the substituents are positioned as far apart from each other as possible to minimize steric repulsion. This conformation is particularly important in the study of alkanes and their conformations.