2.2 Polar Covalent Bonds and Dipole Moments
3 min read•may 7, 2024
form when atoms share electrons unequally. This uneven sharing creates partial charges, leading to . Understanding how these charges distribute across molecules is key to predicting their behavior and properties.
Molecular polarity affects everything from boiling points to solubility. By learning to calculate and predict molecular dipoles, you'll gain insight into how molecules interact with each other and their environment.
Polar Covalent Bonds and Molecular Polarity
Origins of molecular polarity
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- Molecular polarity determined by sum of individual and lone pair contributions
- Bond dipole moments arise from differences between bonded atoms
- More electronegative atom attracts bonding electrons more strongly, creating partial negative charge () (oxygen in HO)
- Less electronegative atom has partial positive charge () (hydrogen in HO)
- contribute to molecular polarity
- Nonbonding electrons held closer to atom, creating partial negative charge () (oxygen in HO, nitrogen in NH)
- Bond dipole moments arise from differences between bonded atoms
- of all bond dipole moments and lone pair contributions determines overall molecular
- Bond dipole moments and lone pair contributions cancel each other out, molecule is (CO, CCl)
- Bond dipole moments and lone pair contributions do not cancel each other out, molecule is (HO, NH)
- distribution affects molecular polarity
Calculation of dipole moments
- Dipole moment () measures polarity of molecule
- Calculated using formula:
- : magnitude of partial charges (Coulombs)
- : distance between partial charges (meters)
- Unit for dipole moment is (D)
- 1 D = 3.336 × 10 C·m
- Calculated using formula:
- Calculating dipole moment:
- Determine partial charges () on atoms based on electronegativity differences
- Measure distance () between partial charges
- Multiply partial charge () by distance () to obtain dipole moment ()
Prediction of molecular dipoles
- Molecular geometry and symmetry crucial in determining presence and direction of dipole moments
- Molecules with symmetric charge distribution are nonpolar
- CO: linear geometry, opposing bond dipoles cancel out
- CCl: geometry, bond dipoles cancel out
- BF: geometry, bond dipoles cancel out
- Molecules with asymmetric charge distribution are polar
- HO: , bond dipoles and lone pairs create net dipole
- NH: geometry, bond dipoles and lone pair create net dipole
- CHCl: tetrahedral geometry, C-Cl bond dipole creates net dipole
- Molecules with symmetric charge distribution are nonpolar
- Predicting presence and direction of dipole moments:
- Identify molecular geometry using
- Determine individual bond dipole moments based on electronegativity differences
- Consider contribution of lone pairs to overall molecular polarity
- Visualize vector sum of all bond dipole moments and lone pair contributions
- Vector sum is zero, molecule is nonpolar
- Vector sum is non-zero, molecule is polar, direction of dipole moment is from positive to negative end of molecule
- affects the overall dipole moment of a molecule
Molecular Structure and Polarity
- help visualize electron distribution and predict molecular polarity
- are influenced by molecular polarity
- helps compare relative polarity of different molecules
Key Terms to Review (34)
Bent Geometry: Bent geometry refers to the angular arrangement of atoms in a molecule, where the central atom forms bonds with two or more other atoms resulting in a non-linear, or bent, molecular structure. This geometric configuration is a key characteristic of polar covalent bonds and the determination of dipole moments.
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 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 Dipole Moments: A bond dipole moment is the separation of charge within a covalent bond, resulting in a partial positive charge on one atom and a partial negative charge on the other. This unequal distribution of charge creates a dipole, which is a key concept in understanding the polarity of molecules.
Carboxylic acid, RCO2H: Carboxylic acids are organic compounds characterized by the presence of at least one carboxyl group (-COOH), where "R" represents the rest of the molecule that can be varying carbon-containing structures. These acids are widely recognized for their sour taste and strong odors, playing pivotal roles in biochemical processes and industrial applications.
CCl4: CCl4, or carbon tetrachloride, is a colorless, dense liquid with a characteristic sweet odor. It is a halogenated organic compound consisting of one carbon atom bonded to four chlorine atoms. CCl4 is an important molecule in the context of understanding polar covalent bonds and dipole moments.
CH3Cl: CH3Cl, also known as methyl chloride, is a simple organic compound consisting of a central carbon atom bonded to three hydrogen atoms and one chlorine atom. This chemical formula and structure are essential in understanding the concepts of polar covalent bonds and dipole moments.
CO2: Carbon dioxide (CO2) is a colorless, odorless gas that is a byproduct of cellular respiration and combustion processes. It is a crucial molecule in the context of polar covalent bonds and dipole moments, as well as the conversion of pyruvate to acetyl CoA during cellular metabolism.
Debye: Debye is a unit used to measure the strength of a molecular dipole moment, which is the measure of the separation of positive and negative electrical charges within a molecule. It is named after the Dutch physicist Peter Debye, who made significant contributions to the understanding of dipole moments and their role in molecular structure and properties.
Debyes (D): Debyes are a unit of measurement used to express the dipole moment of a chemical bond or molecule, indicating the strength and direction of its electrical polarity. One Debye is approximately 3.33564 × 10^-30 Coulomb-meters.
Dipole moment: A dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating the direction and magnitude of polarity. It arises when atoms in a bond share electrons unequally due to differences in electronegativity.
Dipole moment, μ: A dipole moment is a measure of the separation of positive and negative charges in a molecule, indicating the molecule's overall polarity. It is calculated as the product of the charge difference and the distance between the charges.
Dipole Moments: A dipole moment is a measure of the separation of electric charge within a molecule or system. It arises when there is an unequal distribution of electrons, resulting in a partial positive charge on one side and a partial negative charge on the other side of the molecule. Dipole moments are a crucial concept in understanding the polarity of covalent bonds and the overall polarity of molecules.
Electron Density: Electron density refers to the distribution and concentration of electrons within a molecule or an atom. It is a fundamental concept in quantum mechanics and plays a crucial role in understanding the properties and behavior of chemical species.
Electronegativity: Electronegativity is a measure of an atom's ability to attract shared electrons in a chemical bond. It is a fundamental concept in understanding the nature and strength of chemical bonds, as well as predicting the polarity and reactivity of molecules.
Electronegativity (EN): Electronegativity is a measure of an atom's ability to attract and hold onto electrons when it is part of a compound. The higher the electronegativity value, the more strongly an atom can pull electrons towards itself.
H2O: H2O, commonly known as water, is a chemical compound consisting of two hydrogen atoms and one oxygen atom. It is a polar molecule that plays a crucial role in various chemical and biological processes, particularly in the context of polar covalent bonds and dipole moments.
Intermolecular forces: Intermolecular forces are the forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). They are crucial for determining the physical properties of substances, such as boiling points, melting points, and solubilities.
Intermolecular Forces: Intermolecular forces are the attractive or repulsive forces that exist between molecules, which determine the physical and chemical properties of substances. These forces play a crucial role in the context of polar covalent bonds and dipole moments, as well as noncovalent interactions between molecules.
Lewis structures: Lewis structures are visual representations of the valence electrons in molecules, showing how atoms are bonded together and the lone pairs of electrons that may exist. They serve as a foundational tool in organic chemistry for understanding molecular geometry, bonding, and reactivity.
Lewis Structures: Lewis structures are a graphical representation of the bonding in molecules and polyatomic ions, where shared or unshared electron pairs are shown as lines or dots, respectively. They are used to visualize the arrangement of atoms and the distribution of valence electrons in a chemical species.
Lone Pairs: Lone pairs are pairs of valence electrons that are not involved in covalent bond formation and exist independently on an atom. They are an important concept in understanding the hybridization of certain elements and the polarity of covalent bonds.
Molecular Polarity: Molecular polarity refers to the unequal distribution of electrons within a molecule, resulting in an asymmetric charge distribution and the creation of a dipole moment. This concept is essential in understanding the behavior and properties of molecules in various chemical contexts.
NH3: NH3, also known as ammonia, is a colorless gas with a pungent odor. It is a key compound in the context of polar covalent bonds, dipole moments, as well as acid-base chemistry based on the Brønsted-Lowry definition.
Nonpolar: Nonpolar refers to a molecule or bond in which the electrons are evenly distributed, resulting in no separation of charge or dipole moment. This term is particularly relevant in the context of understanding polar covalent bonds and dipole moments.
Polar: Polarity refers to the unequal distribution of electrons within a chemical bond, resulting in one end of the bond having a partial positive charge and the other end having a partial negative charge. This creates a dipole moment, which is a key characteristic of polar molecules.
Polar covalent bonds: Polar covalent bonds are a type of chemical bond where two atoms share a pair of electrons, but the electrons are not shared equally due to differences in electronegativity between the atoms. This unequal sharing creates a partial positive charge on one atom and a partial negative charge on the other.
Polar Covalent Bonds: Polar covalent bonds are a type of chemical bond where the shared electrons between atoms are unequally distributed, resulting in a separation of charge and the creation of a dipole moment. This type of bond is crucial in understanding the behavior and properties of many chemical compounds.
Polarity Scale: The polarity scale is a measure of the degree of charge separation within a covalent bond, ranging from nonpolar to highly polar. It is a crucial concept in understanding the properties and behavior of molecules, particularly in the context of polar covalent bonds and dipole moments.
Tetrahedral: Tetrahedral refers to a three-dimensional molecular geometry in which a central atom is bonded to four other atoms, forming a shape resembling a pyramid with a triangular base. This arrangement is a fundamental concept in chemistry, particularly in the context of chemical bonding theory, organic chemistry, and stereochemistry.
Trigonal Planar: Trigonal planar is a molecular geometry in which a central atom is bonded to three other atoms, with all four atoms lying in the same plane and forming a triangle. This arrangement is a key characteristic of sp2 hybridized atoms and is observed in many organic compounds, such as ethylene.
Trigonal Pyramidal: Trigonal pyramidal is a molecular geometry in which a central atom is bonded to three other atoms, forming a three-dimensional structure with a triangular base and a single atom at the apex, creating a pyramid-like shape.
Vector Sum: The vector sum, also known as the resultant vector, is the combined effect of two or more vectors acting on an object. It represents the net direction and magnitude of the combined forces or displacements acting on a system.
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.