Mahase Chapter 9 Concepts Flashcards
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Questions and Answers

What is the Valence-Bond Theory?

A model of chemical bonding in which an electron pair bond is formed between two atoms by the overlap of orbitals in the two atoms.

What is an example of orbital overlap in H2?

In the coming together of 2 H atoms to form H2, as the orbitals overlap, electron density is concentrated between the nuclei.

What is an example of orbital overlap in HCl?

The Cl has a configuration of [Ne]3s23p5, and this 3p electron pairs with the single 1s electron from H to form a covalent bond.

What is the relationship between potential energy and orbital overlap?

<p>Increased overlap brings the electrons and nuclei closer together while decreasing electron-electron repulsion.</p> Signup and view all the answers

What is developing the concept of hybrid orbitals?

<p>The concept helps reconcile the notion that covalent bonds are formed from the overlap of atomic orbitals with molecular geometries from the VSEPR model.</p> Signup and view all the answers

What are hybrid orbitals?

<p>An orbital that results from the mixing of different kinds of atomic orbitals on the same atom.</p> Signup and view all the answers

What is hybridization?

<p>The mixing of different types of atomic orbitals to produce a set of equivalent hybrid orbitals.</p> Signup and view all the answers

What is the relationship between the number of electron domains and the number of hybrid orbitals?

<p>The total number of atomic orbitals on an atom remains constant, so the number of hybrid orbitals equals the number of atomic orbitals that are mixed.</p> Signup and view all the answers

What is electron promotion?

<p>The process in which an electron from a lower energy orbital is excited to a higher energy orbital to facilitate bonding.</p> Signup and view all the answers

What is the solution to the dilemma of equivalency: 'sp' hybridization?

<p>The dilemma can be solved by mixing 2s and 2p orbitals to generate new orbitals, with one lobe larger than the other.</p> Signup and view all the answers

What is the diagram representation of 'sp' hybrids in a molecule?

<p>The two new orbitals formed are hybrid orbitals called sp hybrid orbitals.</p> Signup and view all the answers

What are the 'sp2' and 'sp3' hybrid orbitals?

<p>Mixing a specific number of atomic orbitals results in the same number of hybrid orbitals which are equivalent but oriented differently.</p> Signup and view all the answers

What is an example of 'sp2' orbitals in BF3?

<p>In BF3, mixing 2s and two of the 2p atomic orbitals yields three equivalent sp2 hybrid orbitals.</p> Signup and view all the answers

What is an example of 'sp3' orbital in CH4?

<p>In CH4, the bonding involves the overlap of four equivalent sp3 hybrid orbitals on C with the 1s orbitals of H atoms.</p> Signup and view all the answers

What is hybrid bonding in molecules with nonbonding pairs?

<p>Hybridization describes bonding in molecules with nonbonding pairs, for example in H2O where the oxygen has a tetrahedral electron domain geometry.</p> Signup and view all the answers

Why can't expanded-octet molecules cannot be represented by the valence-theory orbital model?

<p>Hypervalent elements cannot form six hybrid orbitals because the energy needed exceeds that returned from bonding.</p> Signup and view all the answers

What is the hybrid orbital summary?

<p>For a given electron domain geometry, hybridization can describe the atomic orbitals used by the central atom in bonding.</p> Signup and view all the answers

What is the step-by-step process of identifying hybrid orbitals?

<p>Draw the Lewis structure, use VSEPR to determine electron domain geometry, then specify the hybrid orbitals needed.</p> Signup and view all the answers

What are sigma (σ) bonds?

<p>A covalent bond in which electron density is concentrated along the internuclear axis.</p> Signup and view all the answers

What are pi bonds?

<p>A covalent bond in which electron density is concentrated above and below the internuclear axis.</p> Signup and view all the answers

Why are pi bonds weaker than sigma bonds?

<p>The sideways orientation of p orbitals in a pi bond makes for weaker overlap.</p> Signup and view all the answers

What is molecular architecture?

<p>The shape and size of molecules; effectiveness of drugs depends on molecular shape and size; relates to 2D Lewis structures and 3D molecular shapes.</p> Signup and view all the answers

What are Lewis structures vs. molecular shapes?

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What are bond angles?

<p>The angles made by lines joining the nuclei of atoms in a molecule, determining the shape of the molecule.</p> Signup and view all the answers

What is the CCl4 molecular shape?

<p>The molecule is tetrahedral with bond angles of 109.5°.</p> Signup and view all the answers

What are conventional ABn molecules?

<p>Molecules with a single central atom bonded to 'n' atoms of the same type, represented by the formula ABn.</p> Signup and view all the answers

What are the possible shapes of AB2 and AB3 molecules?

<p>AB2 can be linear or bent; AB3 can be trigonal planar, trigonal pyramidal, or T-shaped.</p> Signup and view all the answers

What are the five shapes that maximize separation of outer atoms?

<p>Trigonal bipyramid and octahedron.</p> Signup and view all the answers

What is the Valence-Shell Electron-Pair Repulsion (VSEPR) model?

<p>A model predicting geometric arrangements of shared and lone electron pairs around a central atom.</p> Signup and view all the answers

What is a bonding pair?

<p>A pair of electrons shared by two atoms in a Lewis structure.</p> Signup and view all the answers

What is a nonbonding pair/lone pair?

<p>A pair of electrons assigned completely to one atom in a Lewis structure.</p> Signup and view all the answers

What determines the shape of a molecule?

<p>The repulsion between electron pairs, both bonding and nonbonding.</p> Signup and view all the answers

What is an electron domain?

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What is an example involving determining the number of electron domains?

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What is the Valence Shell Electron Pair Repulsion Theory (VSEPR)?

<p>The theory stating that the best arrangement minimizes repulsions among electron domains.</p> Signup and view all the answers

What is electron-domain geometry?

<p>The three-dimensional arrangement of electron domains around an atom according to VSEPR.</p> Signup and view all the answers

What are the electron-domain geometries as a function of the number of electron domains?

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What is molecular geometry?

<p>The arrangement in space of the atoms in a molecule, excluding nonbonding pairs.</p> Signup and view all the answers

How do you predict the shape of a molecule (molecular geometry)?

<p>Use VSEPR to determine electron-domain geometry, then adjust for nonbonding pairs.</p> Signup and view all the answers

What is the step-by-step process of predicting molecular geometry?

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What is an example of determining the molecular geometry of an NH3 molecule?

<p>NH3 has a trigonal pyramidal shape with bond angles deviating from ideal due to a nonbonding pair.</p> Signup and view all the answers

What is an example of predicting molecular geometry of CO2?

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What are the electron domain and molecular geometries for two, three, and four electron domains around a central atom?

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What is the linear electron domain?

<p>The domain with only one molecular geometry: linear with a bond angle of 180°.</p> Signup and view all the answers

What is the trigonal planar electron domain?

<p>Trigonal planar if all domains are bonding (120°) and bent if one is nonbonding (118°).</p> Signup and view all the answers

What is the tetrahedral electron domain?

<p>Tetrahedral (109.5°), trigonal pyramidal (107°), or bent (about 105°).</p> Signup and view all the answers

What is an example involving predicting molecular geometries?

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What is the effect of nonbonding electrons and multiple bonds on bond angles?

<p>Nonbonding pairs decrease bond angles, while multiple bonds increase repulsion.</p> Signup and view all the answers

What are the physical differences between nonbonding and bonding electron pairs?

<p>Bonding pairs experience attraction from both nuclei, while nonbonding pairs primarily from one nucleus.</p> Signup and view all the answers

What is the effect of multiple bonds on bond angles?

<p>Multiple bonds exert greater repulsive forces on adjacent electron domains.</p> Signup and view all the answers

What is an example of the effect of multiple bond angles on CCl2O?

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What are the electron domain geometries of molecules with expanded valence shells?

<p>Molecules can have more than 4 e- pairs; geometries can be trigonal bipyramidal or octahedral.</p> Signup and view all the answers

What are the properties of five electron-domains (trigonal bipyramidal)?

<p>Stable geometry with bonds in axial and equatorial positions.</p> Signup and view all the answers

What are axial positions?

<p>Domains that form a 90° angle with equatorial domains.</p> Signup and view all the answers

What are equatorial positions?

<p>Positions minimizing repulsion, crucial in trigonal bipyramidal shapes.</p> Signup and view all the answers

What are the electron-domain and molecular geometries for five and six electron domains around a central atom?

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What is the trigonal bipyramid electron domain?

<p>Geometry with five domains yielding distinct shapes: trigonal bipyramidal, seesaw, T-shaped, and linear.</p> Signup and view all the answers

What is the octahedral electron domain?

<p>Geometry with six domains leading to octahedral, square pyramidal, and square planar shapes.</p> Signup and view all the answers

What are all possible molecular geometries as a function of ABn?

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What are six electron domains (octahedral)?

<p>Stable arrangement with bond angles of 90°; atoms positioned at vertices of an octahedron.</p> Signup and view all the answers

What is an example involving determining the molecular geometries of molecules with expanded valence shells?

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What are the shapes of larger molecules that deviate from the ABn convention?

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What is an example involving determining the shape of acetic acid?

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What is an example involving predicting bond angles of larger molecules?

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What is a bond dipole?

<p>The dipole moment due to unequal electron sharing in a covalent bond.</p> Signup and view all the answers

What is the overall dipole moment of a molecule?

<p>The vector sum of all bond dipoles, considering both magnitude and direction.</p> Signup and view all the answers

What is an example of determining polarity of a CO2 molecule?

<p>The bond dipoles in CO2 cancel each other, making it nonpolar.</p> Signup and view all the answers

What is an example of determining polarity of an H2O molecule?

<p>H2O is bent, leading to a net dipole moment, making it polar.</p> Signup and view all the answers

What are the six symmetrical shapes for which ABn molecules must be nonpolar?

<p>Linear, trigonal planar, tetrahedral, square pyramidal, trigonal bipyramidal, and octahedral.</p> Signup and view all the answers

What are some examples of polar and nonpolar molecules containing polar bonds?

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What is an example involving determining the polarity of molecules?

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What is the development of the valence-bond theory?

<p>Explains how covalent bonds form through sharing electrons.</p> Signup and view all the answers

Study Notes

Molecular Architecture

  • Molecular architecture refers to the shape and size of molecules, critical for drug effectiveness.
  • The relationship between two-dimensional Lewis structures and three-dimensional shapes is essential.

Lewis Structures vs. Molecular Shapes

  • Lewis structures depict electron arrangements, while molecular shapes represent the spatial arrangement of atoms.

Bond Angles

  • Bond angles are formed by lines connecting atom nuclei in a molecule.
  • The shape and size of a molecule depend on bond angles and lengths.

CCl4 Molecular Shape

  • Carbon tetrachloride (CCl4) has a tetrahedral shape with bond angles of 109° and bond lengths of 1.78 Å.

Conventional ABn Molecules

  • ABn molecules consist of a central atom (A) bonded to "n" identical atoms (B).
  • The shape of ABn molecules varies with "n"; examples include CO2 (AB2) and NH3 (AB3).

Possible Shapes of AB2 and AB3 Molecules

  • AB2 can be linear (180°) or bent.
  • AB3 typically has trigonal planar (120°) or trigonal pyramidal shapes, with some being T-shaped.

Maximum Separation Shapes

  • Five shapes maximize distances between outer atoms: trigonal bipyramidal and octahedral.

Valence-Shell Electron-Pair Repulsion (VSEPR) Model

  • This model predicts geometric arrangements based on electron pair repulsions around a central atom.
  • It helps explain molecular shapes, especially for representative elements.

Bonding Pair

  • A bonding pair of electrons is shared between two atoms, defining a region of electron density.

Nonbonding Pair/Lone Pair

  • A nonbonding pair of electrons is located on one atom; affects molecular shape but not the structure directly.

Determinants of Molecular Shape

  • Electron pairs repel each other, allowing predictions on molecule shape based on their arrangement.

Electron Domain

  • An electron domain consists of bonding or nonbonding pairs around a central atom.

Predicting Molecular Geometry

  • The VSEPR model aids in discerning the electron domain geometry, guiding the prediction of molecular shapes.

Molecular Geometry Definition

  • Molecular geometry pertains to the arrangement of only the atoms in a molecule, excluding nonbonding pairs.

Effects of Nonbonding Electrons on Bond Angles

  • The presence of nonbonding pairs alters bond angles compared to idealized geometries due to increased repulsion.

Multiple Bonds and Bond Angles

  • Multiple bonds exert greater repulsive forces compared to single bonds, influencing adjacent bond angles.

Expanded Valence Shells

  • Atoms in period 3 and beyond can accommodate more than four electron pairs, resulting in octahedral or trigonal bipyramidal geometries.

Electron-Domain Geometries

  • Various geometries arise from two to six electron domains around a central atom, influencing molecular shapes.

Symmetrical Shapes and Molecular Polarity

  • Certain symmetrical configurations lead to nonpolar molecules despite individual bond polarities.

Bond Dipole and Overall Dipole Moment

  • A bond dipole is linked to unequal electron sharing, contributing to the overall dipole moment, derived from vector summation of individual bond dipoles.

Valence-Bond Theory Development

  • This theory explains chemical bonding as resulting from orbital overlap, focusing on the concentration of electron pairs between atoms.

Orbital Overlap Examples

  • In H2, electron density forms between nuclei due to overlapping orbitals.
  • HCl exhibits orbital overlap between hydrogen and chlorine, leading to covalent bonding.

Relationship Between Potential Energy and Orbital Overlap

  • Optimal overlap reduces energy due to increased attraction, but excessive proximity raises energy due to nuclear repulsion.

Concept of Hybrid Orbitals

  • Hybrid orbitals reconcile bonding through orbital overlap with geometrical shapes predicted by the VSEPR model.### Hybrid Orbitals
  • Hybrid orbitals are formed by mixing different atomic orbitals (e.g., sp3 hybrid from one s and three p orbitals).
  • They explain the equivalent bond formations around a central atom.

Hybridization

  • Mixing atomic orbitals generates equivalent hybrid orbitals.
  • This mathematical process aids in understanding bond equivalency around central atoms.

Electron Domains and Hybrid Orbitals

  • The number of hybrid orbitals corresponds to the number of atomic orbitals mixed.
  • Specific hybridizations relate to molecular geometries:
    • linear (sp),
    • bent (sp2, sp3),
    • trigonal planar (sp2),
    • tetrahedral (sp3).
  • The number of electron domains determines the type of hybridization.

sp Hybrid Orbitals

  • "sp" hybridization involves mixing one s and one p orbital to create two equivalent sp hybrid orbitals.
  • These orbitals point in opposite directions, facilitating linear arrangements.

Diagram Representation of sp Hybrids

  • sp hybrid orbitals are depicted with one large lobe and one smaller lobe.
  • The hybridization supports a linear arrangement of electron domains.

sp2 and sp3 Hybrid Orbitals

  • Combining different atomic orbitals produces equivalent hybrid orbitals that point in varying directions.
  • sp2 hybrid orbitals (2s + 2p) yield a trigonal planar geometry, while sp3 hybrid orbitals (1s + 3p) yield tetrahedral geometry.

Examples of sp2 Orbitals in BF3

  • In BF3, three equivalent sp2 orbitals form bonds with fluorine atoms, leading to a trigonal planar structure with 120° angles.
  • An unhybridized p orbital remains.

Examples of sp3 Orbital in CH4

  • CH4 features four sp3 hybrid orbitals arranged tetrahedrally, facilitating distinct bonding with hydrogen atoms.

Hybrid Bonding with Nonbonding Pairs

  • Hybridization also describes bonding in molecules with lone pairs, as seen in H2O, where two sp3 hybrid orbitals contain lone pairs, and the other two form bonds with hydrogen atoms.

Limitations of the Valence Theory Orbital Model

  • Expanded-octet molecules require more than the standard model allows, as hybridization must consider energy levels.
  • For hypervalent elements, the model fails to effectively represent bonding in compounds like SF6.

Hybrid Orbital Summary

  • Knowing the electron domain geometry allows prediction of hybridization types:
    • 2 electron domains = sp (linear)
    • 3 electron domains = sp2 (trigonal planar)
    • 4 electron domains = sp3 (tetrahedral)

Process of Identifying Hybrid Orbitals

  • Draw the molecule's Lewis structure.
  • Use VSEPR theory to ascertain electron domain geometry.
  • Identify the corresponding hybrid orbitals based on the arrangement of electron pairs.

Valence Bond Theory

  • Covalent bonds form through overlapping atomic orbitals, resulting in sigma (σ) and pi (π) bonds.
  • Sigma bonds involve electron density between atomic nuclei, providing strong bond strength.

Sigma Bonds

  • Characterized by concentrated electron density along the internuclear axis.
  • Formed via overlaps of atomic orbitals (s-s or s-p).

Pi Bonds

  • Feature electron density above and below the internuclear axis.
  • A double bond consists of one σ and one π bond; a triple bond consists of one σ and two π bonds.

Strength of Bonds

  • π bonds are generally weaker than σ bonds due to the less effective sideways overlap of p orbitals.
  • σ bonds benefit from strong attraction between electron clouds and atomic nuclei due to their positioning.

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Explore the fundamental concepts of Molecular Architecture and Lewis Structures through these flashcards. Understand how the shape and size of molecules influence drug effectiveness and the distinction between two-dimensional representations and three-dimensional molecular shapes.

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