Chapter 2 Bonding and Structure of Organic Compounds - Until Index of Hydrogen Deficiency

Ionic

Covalent

Ionic Compound
Covalent Compound

__________ bond – electrons are transferred from one atom to another

__________ bond – one or more pairs of electrons are shared between atoms

__________ compounds contain charged particles held together by extremely strong electrostatic interactions.

__________ - It is a compound whose structural units are called molecules. A molecule is a neutral collection of atoms held together by covalent bonds.

Bond length

Bond strength

Bond angle

Bond polarity

_____________ - the equilibrium distance between the nuclei of two atoms that are bonded to each other

_____________ - alternative name for bond dissociation energy - the amount of energy needed to break a bond homolytically and produce two radical fragments

_____________ - the angle formed between two adjacent bonds

_____________ - a measure of the distribution of electrons between two bonded atoms

consumed; liberated

Bond strength

the amount of energy ___________ when a bond is broken is equal to the amount of energy ____________ when a bond is formed

Electronegativity

_________________ - intrinsic ability of an atom to attract the shared electrons in a covalent bond

Dispersion or London Forces

polarizability

surface area

Polarizability

Factors that affect the magnitude of London dispersion forces:

a. relative ______________ of electrons of the atoms involved

b. relative ______________ of the molecules involved

_____________ – a measure of how the electron cloud around an atom responds to changes in its electronic environment

Dipole-dipole

_________________ forces - an interaction between molecules having permanent dipole moments

Hydrogen bonds

________________ - a strong dipole-dipole interaction that occurs between hydrogen atoms bonded to small strongly electronegative atoms and the nonbonding electron pairs on other such electronegative atoms

Quantum Mechanical Model of the Atom

_________________________ - the motion of an electron around a nucleus can be described mathematically by a wave equation

orbital

shell

node

___________ - a wave function which describes the volume of space around a nucleus in which an electron is most likely to be found

_____________ - a group of an atom’s electrons with the same principal quantum number

________ - region of zero electron density

Aufbau
Pauli exclusion

Hund’s rule

___________ principle - rules for determining the electron configuration of an atom

_______________ principle - no more than two electrons can occupy the same orbital, and those two electrons must have spins of opposite sign

______________ - if two or more empty orbitals of equal energy are available, one electron occupies each, with their spins parallel, until all are half-full

Valence Bond Theory (VBT)

Key ideas of VBT

a) covalent bonds are formed by overlap of two atomic orbitals, each of which contains one electron

b) each of the bonded atoms retains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms

c) the greater the amount of orbital overlap, the stronger the bond

________________ - a covalent bond results when two atoms approach each other closely so that a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom

Molecular Orbital Theory (MOT)

Key ideas of MOT

a) molecular orbitals are to molecules what atomic orbitals are to atoms

b) molecular orbitals are formed by combining atomic orbitals

the number of molecular orbitals formed is equal to the number of atomic orbitals combined

c) relative energies of molecular orbitals:

• bonding MO (lower E than AO)

• nonbonding MO (same E as AO)

• antibonding MO (higher E than AO)

__________________ - describes covalent bond formation as arising from a mathematical combination of atomic orbitals to form molecular orbitals

Hybridization

______________- combination of two or more atomic orbitals to form the same number of hybrid orbitals, each having the same shape and energy

sp² hybridization

There are two covalent bonds formed between the two carbon atoms of ethene:

• one σ bond from the end-on overlap of two sp2 hybrid orbitals

• one π bond from the side-to-side overlap of two 2p orbitals

There are three covalent bonds formed between the two carbon atoms of ethyne:

• one σ bond from the end-on overlap of two sp hybrid orbitals

• two π bonds from the side-to-side overlap of two sets of 2p orbitals

Hybridization Summary

Lewis

Kekulé

Structure Writing

__________ structures - valence electrons of an atom are represented as dots
__________ structures - a two-electron covalent bond is indicated as a line drawn between atoms

Formal Charge

________________-

• the electronic charge assigned to individual atoms in a Lewis structure

• the number of valence electrons in an isolated atom minus the number of electrons assigned to that atom in a Lewis structure

• FC = VE – ½ BE - NBE

Resonance structures

______________________

• two or more structures of a molecule that differ in the placement of pi (π) bonds and nonbonded electrons

• the placement of atoms and sigma (σ) bonds stay the same

• the true structure is a composite or hybrid of the different contributing structures

Rules for Resonance Forms

Rules for Resonance Forms

1. Individual resonance forms are imaginary, not real.

2. Resonance forms differ only in the placement of their π or nonbonding electrons.

   • a curved arrow always indicates the movement of electrons, not the movement of atoms

3. Different resonance forms of a substance don’t have to be equivalent

   

4. Resonance forms must be valid Lewis structures and obey normal rules of valency.

   

5. The resonance hybrid is more stable than any individual resonance form.

• Molecular

• Structural

Representation of Structures

• _____________ formula – specifies the actual number of each kind of atom in the molecule

• _____________ formula – shows the connectivity of the atoms in a molecule

Index of Hydrogen Deficiency

• also called degree of unsaturation

• gives a count of how many molecule of H2 needs to be added to a structure in order to obtain the corresponding saturated or acyclic form

ρ = C – ½ H + ½ N – ½ X + 1

What is the formula for the Index of Hydrogen Deficiency?

Index of Hydrogen Deficiency

• takes a count of how many rings or multiple bonds are in the structure

• must be an integer