Write Lewis structures and predict the molecular structures...

Write Lewis structures and predict the molecular structures of the following. (See Exercises 105 and 106 .) a. $\mathrm{OCl}_{2}, \mathrm{KrF}_{2}, \mathrm{BeH}_{2}, \mathrm{SO}_{2}$ b. $\mathrm{SO}_{3}, \mathrm{NF}_{3}, \mathrm{IF}_{3}$ c. $\mathrm{CF}_{4}, \mathrm{SeF}_{4}, \mathrm{KrF}_{4}$ d. $\mathrm{IF}_{5}, \mathrm{AsF}_{5}$ Which of these compounds are polar?

Write Lewis structures and predict the molecular structures of the following. (See Exercises 105 and 106 .)
a. $\mathrm{OCl}_{2}, \mathrm{KrF}_{2}, \mathrm{BeH}_{2}, \mathrm{SO}_{2}$
b. $\mathrm{SO}_{3}, \mathrm{NF}_{3}, \mathrm{IF}_{3}$
c. $\mathrm{CF}_{4}, \mathrm{SeF}_{4}, \mathrm{KrF}_{4}$
d. $\mathrm{IF}_{5}, \mathrm{AsF}_{5}$
Which of these compounds are polar?

Key Concepts

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. While VSEPR theory provides the basic framework for predicting shape based on electron pair repulsion, molecular geometry focuses on the positions of the atoms (ignoring the lone pairs). Common geometries include linear, bent, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral, and the specific geometry has a significant effect on the molecule's physical and chemical properties.

Lewis Structures

Lewis structures are diagrams that represent the valence electrons of atoms within a molecule. They are used to predict how atoms bond to each other, illustrating the distribution of shared and lone electron pairs. Drawing a correct Lewis structure involves counting the total number of valence electrons, assigning electron pairs to form bonds between atoms, and placing remaining electrons as lone pairs to satisfy the octet rule (or duet for lighter atoms).

VSEPR Theory

The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the geometry of a molecule based on the repulsions between electron pairs in the valence shell of the central atom. According to VSEPR, electron pairs, whether in bonds or as lone pairs, will arrange themselves as far apart as possible to minimize repulsion, thereby determining the overall shape of the molecule.

Molecular Polarity

Molecular polarity is determined by the distribution of electrical charge within a molecule, which depends on both the polarity of the individual bonds (due to differences in electronegativity) and the geometry of the molecule. Even if a molecule has polar bonds, its overall polarity may be canceled out by symmetric arrangements of these bonds. Conversely, molecules with an asymmetrical arrangement of polar bonds will have a net dipole moment, making them polar.

Transcript

00:01 Okay, for 121a, you've got ocl2 with two bonded groups and two lone pairs of electrons.

00:08 So this is a bent geometry, and your electronegativities for chlorine and oxygen are 3 and 3 .5.

00:18 So that difference is going to give you a polar bond.

00:21 That means since it's bent, the bond polarities, the bond dipoles won't cancel.

00:25 This is a polar molecule.

00:27 In krf2, you've got two bonded groups.

00:30 And then you've got three lone pairs of electrons on the central atom.

00:34 This is linear and that's a symmetrical geometry.

00:37 So this is going to be a non -polar molecule.

00:40 For beh2, you have two bonded groups, no lone pairs of electrons on the central atom.

00:46 This is linear, which is a symmetrical geometry.

00:49 Since i have the same atoms bonded to the central atom, the bond dipoles cancel, and this is a non -polar molecule.

00:56 For s .o2, i have two bonded groups, one lone pair of electrons on the central atom.

01:00 This is a bent geometry, and i have 2 .5 for the electronegativity on sulfur and 3 .5 on oxygen.

01:09 That difference is going to give me a polar bond.

01:11 And so since those bond dipoles don't cancel since it's bent, it's going to be a polar molecule.

01:16 If we're looking at b, we've got three bonded groups, no lone pairs of electrons.

01:21 This is going to be a trigonal planar geometry.

01:25 And then your bond dipoles will cancel since it's symmetrical.

01:29 So this is a non -polar molecule.

01:32 In nf3, i have three bonded groups, one lone pair of electrons.

01:37 So this is a trigonal pyramidal geometry.

01:41 And my fluorine is four.

01:44 My nitrogen is three in terms of electronegativity.

01:47 That gives me a polar bond.

01:48 The bond dipoles do not cancel because this is not symmetrical.

01:52 So this is going to be a polar molecule...

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