Comprehensive Stereochemistry and Molecular Geometry: VSEPR, Hybridization, and Polarity

What is stereochemistry?

The study of the three-dimensional shapes of molecules.

Who is the principal originator of Valence Shell Electron Pair Repulsion Theory (VSEPR)?

R. J. Gillespie in the 1950s.

What does Valence Bond Theory involve?

The use of hybridized atomic orbitals.

Who is the principal originator of Valence Bond Theory?

L. Pauling in the 1930s and 40s.

What is the first step in predicting molecular structure?

Draw the correct Lewis dot structure.

How is electronic geometry determined according to VSEPR Theory?

By the locations of regions of high electron density around the central atom(s).

What does molecular geometry depend on?

The arrangement of atoms around the central atom(s).

What is the relationship between lone pairs and bond angles?

Lone pairs require more volume than bonding pairs, affecting bond angles.

What defines a polar molecule?

It contains one polar bond or one lone pair of electrons on the central atom, and the arrangement does not allow for cancellation of polarities.

What is hybridization in Valence Bond Theory?

The mixing and exchange of atomic orbitals on the central atom to form hybrid orbitals.

What does the notation AB3U represent?

3 bonding pairs and 1 lone pair around the central atom.

What is the electronic arrangement for AB2 species?

Linear electronic arrangement with no lone pairs on the central atom.

Give an example of a linear, nonpolar molecule.

BeCl2.

What is the electronic arrangement for AB3 species?

Trigonal planar electronic arrangement with no lone pairs on the central atom.

Give an example of a trigonal planar, nonpolar molecule.

BF3.

What is the electronic arrangement for AB4 species?

Tetrahedral electronic arrangement with no lone pairs on the central atom.

Give an example of a tetrahedral, nonpolar molecule.

CH4.

What happens to the molecular geometry if there are lone pairs on the central atom?

The electronic and molecular geometries will differ.

What is the order of strength of repulsions of electrons around a central atom?

lp/lp > lp/bp > bp/bp.

What is the significance of the shape in determining molecular polarity?

The shape influences whether polarities cancel out or not.

What is the effect of lone pairs on molecular geometry?

They can distort the shape and affect bond angles.

What is the electronic geometry of methane (CH4)?

Tetrahedral electronic geometry.

What is the molecular geometry of ammonia (NH3)?

Pyramidal shape with tetrahedral electronic geometry.

What does the term 'regions of high electron density' refer to?

Bonding pairs and lone pairs of electrons around the central atom.

What is the role of electronegativity differences in determining molecular polarity?

They help assess whether bonds are polar and if the overall molecule is polar.

What is the molecular geometry of a molecule with two bonding pairs and one lone pair?

Bent or angular shape.

What is the electronic geometry for a molecule with four bonding pairs?

Tetrahedral electronic geometry.

What is the electronic arrangement of AB4 species with no lone pairs on A?

Tetrahedral with a bond angle of 109.5°.

What is the hybridization of AB4 species?

sp3 hybridization.

Which molecule is an example of an AB4 species?

Methane (CH4).

What is the general formula for alkanes?

CnH2n+2.

What is the shape and polarity of AB3U species with one lone pair on A?

Trigonal pyramidal and polar.

Name an example of an AB3U molecule.

Ammonia (NH3).

What is the electronic arrangement of AB2U2 species with two lone pairs on A?

Bent or angular shape and polar.

Give an example of an AB2U2 molecule.

Water (H2O).

What is the shape of ABU3 species with three lone pairs on A?

Linear shape.

What is the hybridization of the central atom in ABU3 species?

sp3 hybridization.

What is the bond angle distortion caused by lone pairs?

Lone pairs cause repulsion, altering bond angles from ideal geometries.

What is the electronic arrangement of AB5 species?

Trigonal bipyramidal.

What are the axial and equatorial positions in a trigonal bipyramidal structure?

Axial positions are above and below the central atom; equatorial positions are in the same base plane.

What is the bond angle between equatorial positions in a trigonal bipyramidal arrangement?

120°.

What is the bond angle between axial and equatorial positions in a trigonal bipyramidal arrangement?

90°.

What is the shape of AB4U molecules?

Seesaw shape and polar.

Provide an example of an AB4U molecule.

SF4.

What is the shape of AB3U2 molecules?

T-shaped and polar.

Give an example of an AB3U2 molecule.

IF3.

What is the shape of AB2U3 molecules?

Linear shape and nonpolar.

Provide an example of an AB2U3 molecule.

XeF2.

What is the electronic arrangement of AB6 species?

Octahedral.

What is the hybridization of the central atom in AB6 species?

sp3d2 hybridization.

What happens to the shape of octahedral molecules when lone pairs are present?

They can form new shapes such as square pyramidal or square planar.

What is the shape of molecules with six bonding pairs and all substituents the same?

Octahedral and nonpolar.

Name an example of an octahedral molecule.

SF6.

What shape does a molecule with one lone pair and five bonding pairs have?

Square pyramidal

What shape does a molecule with two lone pairs and four bonding pairs have?

Square planar

Why do lone pairs occupy axial positions in octahedral arrangements?

They are 90° from four bonding pairs, resulting in decreased repulsions.

What is the hybridization of the iodine atom in IF5?

sp3d2

What is an example of an AB5U molecule?

IF5

What is the hybridization of the xenon atom in XeF4?

sp3d2

What is an example of an AB4U2 molecule?

XeF4

What is the simplest organic compound containing a double bond?

Ethene (C2H4)

What is the Lewis dot formula calculation for ethene?

N = 2(8) + 4(2) = 24; A = 2(4) + 4(1) = 12; S = 12

What hybridization do carbon atoms in ethene undergo?

sp2 hybridization

What type of bond results from the head-on overlap of sp2 hybrid orbitals?

σ bond

What type of bond results from the side-on overlap of p orbitals in a double bond?

π bond

What is the simplest organic compound containing a triple bond?

Ethyne (C2H2)

What is the Lewis dot formula calculation for ethyne?

N = 2(8) + 2(2) = 20; A = 2(4) + 2(1) = 10; S = 10

What hybridization do carbon atoms in ethyne undergo?

sp hybridization

How many bonds does a triple bond consist of?

One σ bond and two π bonds

What is the first step in predicting molecular geometry?

Draw the Lewis structure.

What does VSEPR theory help determine?

The electron group geometry around the central atom.

What is the bond angle for a linear shape?

180°

What is the bond angle for tetrahedral geometry?

109.5°

What is the bond angle for trigonal bipyramidal geometry?

120° and 90°

What is the bond angle for octahedral geometry?

90°

What does the term 'polar molecule' refer to?

A molecule with a net dipole moment due to polar bonds.

How does molecular polarity affect solubility in water?

Polar molecules dissolve well in water due to attraction.

What is Valence Bond Theory?

A theory that describes chemical bonding based on the overlap of atomic orbitals.

What is the geometry of an atom with four electron groups?

Tetrahedral

What hybridization is used for an atom with five electron groups?

sp3d

What hybridization is used for an atom with six electron groups?

sp3d2