1 - Molecular Structure

Question 1

Rules for Lewis Dot Structures:

1)

2)

3)

Answer 1

1) Find the total number of valence electrons for all atoms in the molecule.
2) Use on pair of electrons to form one bond between each atom.
3) Arrange the remaining electrons around the atoms to satisfy the duet rule for hydrogen and the octet rule for other atoms.

Question 2

The Valency of Carbon, Nitrogen, Oxygen, and Hydrogen

Answer 2

Carbon= tetravalent
Nitrogen= trivalent
Oxygen= divalent
Hydrogen and halogen= monovalent

Question 3

Formal charge=

Answer 3

is the number of electrons in the isolated atom, minus the number of electrons assigned to the atom in the lewis structure.

Question 4

Index of hydrogen deficiency definition and formula?

Answer 4

indicates the number of pairs of hydrogens a compound requires in order to become a saturated alkane. (n= number of carbons & x= number of hydrogens)

_(2n + 2) - x_
  2

Question 5

electrostatic force=

***lowest energy for those that are…***

Answer 5

between the electrons and the nuclei that creates all molecular bonds.

***lowest potential energy level for those objects that are closest together. Electrons are at the lowest energy when they form a bond because they minimize distance from the nuclei.***

Question 6

Sigma bond=

Answer 6

when the bond is directly between two bonding atoms.

Since they are so close they have a positive charge (electrons), and the lowest energy making it a very stable form of covalent bonds.

VERY STRONG; and the first bond to be form ALWAYS between two atoms.

Question 7

Pie bond=

Answer 7

any new bonds in addition to sigma bond. Each additional bond shortens the distance between the two atoms.

They are higher in energy, weaker, and are therefore more reactive; Carbon, nitrogen, oxygen, sulfur, and phosphorous all form pie bonds. Pie bonds prevent rotation!

Question 8

Hyrbid orbitals:

Answer 8

sp, sp2, sp3

Sp—> 180 degree—> linear
Sp2–> 120 degree—>trigonal planar
Sp3–> 109.5 degree–>tetrahedral, pyramidal, or bent

Dsp3–> 90, 120 degree–> trigonal-bypyramidal, seesaw, t-shaped, linear
D2sp3–> 90 degree–> octahedral, square pyramidal, square planar

Question 9

Resonance Structures:

Answer 9

molecules containing delocalized electrons can be represented by a combination of two or more Lewis structures called resonance structures.

Question 10

Dipole Moment:

Answer 10

occurs when the center of positive charge on a molecule or bond does not coincide with the center of negative charge.

u= qd (q is the magnitude, and d is the distance between centers of charge) molecule or bond which has a dipole moment is referred to as polar, and one without a dipole moment is considered non-polar!

Question 11

Induced dipoles:

Instantaneous dipole moment:

Answer 11

the polar molecule or ion creates an electric field, which pushes the electrons and nuclei in opposite directions, separating the centers of positive and negative charge. Weaker than constant dipoles.

arise because the electrons in a bond move about the orbital, and at any given moment may not be distributed exactly between the two bonding atoms even when the atoms are identical.

Question 12

Intermolecular attractions:

Hydrogen bond:

London dispersion forces:

Answer 12

attractions between separate molecules, occur solely due to dipole moments.

the intermolecular bond formed between H+ and nitrogen, oxygen, fluorine on another atom. Strongest type of dipole-dipole interaction. Responsible for the high boiling point of water.

the weakest of dipole-dipole forces (two instantaneous dipoles) BUT they are responsible for the phase changes of nonpolar molecules.

Question 13

Conformational Isomers:

Strutural Isomer:

Answer 13

are not true isomers. They are different spatial orientations of the same molecule. Newman projections: eclipsed, fully eclipsed, antistaggered, and gauche.

have the same molecular formula but different bond-to-bond connectivity.

Question 14

Chirality=

Chiral molecules=

Answer 14

the “handedness” of the molecule.

differ from their reflections; while achiral molecules are exactly the same as their reflections. Any carbon is chiral when it is bonded to four different substituents.

Question 15

Absolute configuration:

Relative configuation:

Answer 15

R and S. CCW=S; CW=R

two molecules that have the same relative configuration about a carbon if they differ by only one substituent and the other substituents are oriented identically about the carbon.

Question 16

Observed rotation:

Specific Rotation:

Answer 16

direction and the degree to which a compound rotates plane-polarized light.

is simply a standardized form of observed rotation that is arrived through calculations using observed rotation and exp. Parameters.

Question 17

Optically inactive:

Optically active

Answer 17

compounds may be compounds with no chiral centers, or they may be chiral compounds containing equal amount of both stereoisomers; called racemic mixture.

if it rotates plane-polarized light to the right or “d/+”, or to the left “l/-“

Question 18

Stereoisomers:

Geometric:

Answer 18

two molecules with the same molecular formula and the same bond-to-bond connectivity that are not the same compound.

cis and trans isomers. Cis have a dipole moment, while trans do not; and they have different physical characteristics!

Question 19

Enantiomers:

Diastereomers:

Answer 19

have the same molecular formula, have the same bond-to-bond connectivity, are mirror images of each other, but are not the same molecule. Opposite absolute configurations are each chiral carbon. Resolution= the separation of enantiomers.

have the same molecular formula, have the same bond-to-bond connectivity, are not mirror images to each other, and are not the same compound.

Question 20

Steric hindrance:

E–>

Z–>

***maximum number of optically active isomer

Answer 20

the substituent groups in the cis position may crowd each other…

E–> opposite
Z–> together

***maximum number of optically active isomers= 2^n; n= chiral centers.***

Question 21

Meso compound:

Epimers:

Coordinate covalent bond:

Answer 21

two chiral centers in a single molecule may offset each other creating an optically inactive molecule.; making them achiral and optically inactive.

diastereomers that differ at only one chiral carbon. These can transfer into anomers when the molecule makes a ring like glucose.

one nucleus can donate both electrons, instead of just one in like a regular covalent bond.