CH. 1 - ATOMS AND MOLECUES; ORBITALS AND BONDINGlightcat-files.s3.amazonaws.com/packets/admin... ·...

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ORGANIC - JONES 5E

CH. 1 - ATOMS AND MOLECUES; ORBITALS AND BONDING

CONCEPT: WHAT IS ORGANIC CHEMISTRY?

Organic Chemistry is the chemistry of life. It consists of the study of molecules that are (typically) created and used by biological systems.

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Technically, an organic molecule is any molecule that contains both __________and ___________.

An organic molecule that contains a mixture of carbon and hydrogen solely is called a ___________________

EXAMPLE: Which molecules are organic? Which of them are also hydrocarbons?

ORGANIC - JONES 5E


CONCEPT: ATOMIC STRUCTURE

The atom is the basic unit of matter.

● The atomic number of an atom is equal to the number of ____________

● The mass number of an atom is equal to

______________________ + ________________________

● Isotopes have the same atomic number but have differing _______________________

EXAMPLE: Hydrogen Isotopes

● Electrons orbit the nucleus in a region of space that is called a ___________

● The region of space within a shell with exactly enough space for a pair of electrons (up/down spin) is called an ________

● When atoms possess a different number of electrons than protons, they are called __________

● Positively charged atoms are called ______________ ● Negatively charged atoms are called ______________

EXAMPLE: Hydrogen Ions

Three Principles of Electron Configuration

ORGANIC - JONES 5E


PRACTICE: Determine the number of protons, neutrons and electrons in the following atoms.

a. b.

PRACTICE: Determine which of the three principles of electron configuration is being broken in the electron diagrams below.

c.

d.

ORGANIC - JONES 5E


CONCEPT: WAVE FUNCTIONS

Quantum Mechanics states that electrons behave both as particles and as ____________.

● The Heisenberg Uncertainty Principle states that we cannot simultaneously know an electron’s speed and ___________

□ Equations called wave functions correspond to the energy state of a given electron ______

□ The relative probability of finding an electron can be derived from the wave function ______

□ The 3-D plot of the _______ is called an atomic _____________: where the chance of finding electrons is high.

As with any type of wave, wave functions have the ability to ________________ with each other upon meeting. ● This can occur either constructively or destructively

EXAMPLE: H2 Molecular Orbitals

ORGANIC - JONES 5E


CONCEPT: MOLECULAR ORBITALS

When atomic orbitals overlap constructively, they create unusual regions of shared electron density called __________

● The type of bond created is determined by how many regions are overlapping

We can use a model called the Linear Combination of Atomic Orbitals (LCAO) using addition and subtraction of orbitals to

indicate the type of interference. This way we can determine the mathematical energy levels of all possible molecular orbitals.

EXAMPLE: H2 LCAO

EXAMPLE: C2 LCAO (simplified)

ORGANIC - JONES 5E


CONCEPT: BOND SUMMARY EXAMPLE: Determine the number of σ-bonds and π-bonds in the following molecules

a. b. PRACTICE: Rank the following bonds from shortest to longest

ORGANIC - JONES 5E


CONCEPT: THE OCTET RULE

Atoms are most stable when they achieve the number of electrons necessary to reach a Noble Gas Configuration.

□ The tendency for atoms to lose or gain electrons in order to reach this configuration is known as the __________ rule

We can use MO theory to prove why atoms are most stable (and will not form bonds) in the Noble gas configuration

EXAMPLE: He2 LCAO

Atoms can satisfy their octet through forming chemical bonds or by possessing lone pairs. These are called octet electrons.

□ First-row elements (H, He, Li) will prefer to possess _____ octet electrons

□ Second-row elements (C, N, O, F) will prefer to possess _______ octet electrons

● Atoms smaller than Carbon will possess less than 8 electrons: (Be) ______ and (B) ________

□ Third-row elements may form expanded octets that can hold (P) _____ and (S) _______

ORGANIC - JONES 5E


CONCEPT: BONDING PREFERENCES

There may be many ways to combine octet electrons to satisfy the octet rule for a certain atom:

● _________________ electrons are the name we give to the octet electrons that the atom actually “owns”. The number of

these determines which of the possible octets will be the most stable.

□ An atom owns every lone electron it has

□ An atom owns ___ electron for every bond that it has

EXAMPLE: Find the total number of octet electrons and valence electrons in the following hydrocarbons. Do all of these

compounds satisfy the octet rule? If so, are they all equally stable?

The amount of electrons that the valence shell of each 2nd row element prefers to “own” is determined by its group number

on the periodic table. This will determine how many bonds it wants to have in its most stable state.

ORGANIC - JONES 5E


CONCEPT: FORMAL CHARGES

Whenever there is a difference between the number of valence electrons that an atom has and its group number, a formal

charge is assigned.

FORMAL CHARGE = Group # - Valence Electrons

● The __________________ is the term that we give to the SUM of all the formal charges of a molecule.

EXAMPLE: Calculate the formal charges of ALL atoms.

PRACTICE: Calculate the formal charges of ALL atoms. Indicate if the molecule has a net charge.

a.

b.

ORGANIC - JONES 5E


CONCEPT: BONDLINE STRUCTURES

The bondline method is a way to simplify the drawings of organic structures, based on the octet rule.

● _____________ are implied: Every corner is assumed to represent a carbon.

● _____________ are implied: Carbon is assumed to possess enough hydrogens to fill its octets.

● _____________ are implied: Heteroatoms are assumed to possess enough electrons to fill their octets.

● ____________ _____________ are used to indicate when an atom does not satisfy its bonding preference.

□ Watch Out: ALL hydrogens on ______________________________ MUST be drawn explicitly.

EXAMPLE: Conversion of ethanol to bondline

PRACTICE: How many implied hydrogens does each labeled carbon have?

a.

b.

ORGANIC - JONES 5E


PRACTICE: Convert each structure into a line-angle structure. Be sure to assign ALL necessary formal and net charges.

a.

b.

c.

d.

ORGANIC - JONES 5E


CONCEPT: LEWIS STRUCTURES Lewis structures are used to determine chemical structures based on based on the octet rule and bonding preferences.

1. Draw the atom with highest bond preference in the middle and propose a σ-bond framework. a. If two atoms have the same bonding preference, place the bigger one in the center

2. Complete octets using lone pairs 3. Calculate the theoretical number of valence electrons 4. Calculate the actual number of valence electrons 5. Actual – Theoretical = Electron Difference

a. If electron difference is positive, create double bonds b. If electron difference is negative, add lone pairs.

EXAMPLE: N2H4 Lewis Structure PRACTICE: Draw the Lewis Structure for the following molecules: HCN

ORGANIC - JONES 5E


PRACTICE: Draw the Lewis Structures for the following molecules a. HNO3 b. H2CO3

ORGANIC - JONES 5E


CONCEPT: CONDENSED STRUCTURES

The condensed method is a common way to describe the _________________________ of a molecule using only text.

● Know how to quickly interconvert between __________________ and condensed

EXAMPLE: Full Condensed Structure

EXAMPLE: Condensed Mixed Structure

PRACTICE: Convert the following condensed structures into bondline

CH2Br(CH2)3CH(CH2CH3)2

ORGANIC - JONES 5E


CONCEPT: RESONANCE STRUCTURES

Resonance theory is used to represent all the different ways that the same molecule can distribute its electrons.

● Atoms ____________ move! The only thing that moves is ______________________

● ________ of these contributing structures will be a realistic representation of what the molecule actually looks like

Rules:

● Use curved arrows to represent electron movement

● Use double-sided arrows and ________________ to link related structures to each other

● Arrows always travel from region of ___ electron density to ___ electron density

● The net charge of each structure must be _____________________

EXAMPLE: Common forms of resonance

ORGANIC - JONES 5E


PRACTICE: Draw all of the contributing structures for the following molecules

a.

b. c.

ORGANIC - JONES 5E


CONCEPT: RESONANCE HYBRIDS

The resonance hybrid represents the mathematical combination of all the contributing structures

● It indicates where the resonating electrons within the molecule are _____________________ to reside

EXAMPLE: Isocyanate Resonance Hybrid

CONCEPT: MAJOR CONTRIBUTORS

Often one of the resonance structures will be more _________ so it will contribute to the __________ more than the others.

Major contributors will often have the following characteristics:

● _______________ structures are almost always more stable than charged ones

□ If possible, every atom should fill its ___________

□ Use electronegativity trends to determine best placement of charges

EXAMPLE: Isocyanate major contributor

ORGANIC - JONES 5E


PRACTICE: Draw all of the contributing structures for the following molecules. Label the major contributor if applicable and draw the resonance hybrid.

a.

b.

ORGANIC - JONES 5E


CONCEPT: ELECTRONEGATIVITY

Chemical bonds are formed when the sharing of valance electrons between two or more atoms takes place.

● The _____________ of sharing will determine the identity and strength of the chemical bond.

● An unequal sharing of electrons in one direction along a bond is called a __________ _____________ (______)

● The charge between any two bonded atoms is related to their difference in electronegativity

Generalizations:

● Bonds to carbon and hydrogen are always _______________

● Bonds between two identical atoms are always _________________

□ Adjacent atoms on the periodic table are _____________

□ Lone pairs are ____________

● ________ ________________ exist when atoms have asymmetrical dipoles

ORGANIC - JONES 5E


PRACTICE: Which of the following molecules contain dipoles? Which contain net dipoles?

PRACTICE: Which of the solvents below is apolar? Which is polar?

ORGANIC - JONES 5E


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