CH231 Chapter 1: Covalent Bonding & Shapes of Molecules

Vocabulary flashcards covering atomic structure, electronic configurations, bonding models (Lewis, VB, MO), hybridization, and functional groups in organic chemistry.

Organic Chemistry

The study of the compounds of carbon.

Principle energy levels (shells)

Regions of space where electrons are confined, designated by $n = 1, 2, 3, 4\text{...}$ and capable of holding $2n^2$ electrons.

Orbitals

Subshells within shells designated by the letters $s$, $p$, $d$, and $f$, which represent specific regions of electron density.

Aufbau (“Build-Up”) Principle

The principle stating that orbitals fill in order of increasing energy, from lowest to highest.

Pauli Exclusion Principle

The rule that no more than two electrons may be present in an orbital, and if two are present, their spins must be paired.

Hund’s Rule

The rule that when orbitals of equal energy are available, one electron is placed in each before a second is added, with the spins of single electrons aligned.

Energy-level diagram

A pictorial designation of the electron configuration of an atom, showing where electrons are placed in the ground state.

Valence shell

The outermost occupied electron shell of an atom.

Valence electrons

Electrons in the outermost shell of an atom used to form chemical bonds and participate in chemical reactions.

Lewis dot structure

A representation where the symbol of an element represents the nucleus and inner shell electrons, and dots represent valence electrons.

Ionic bond

A chemical bond formed by the electrostatic attraction between anions and cations.

Covalent bond

A chemical bond formed by the sharing of electron pairs between atoms.

Polar covalent bond

A chemical bond where electrons are shared unequally, resulting in partially ionic and partially covalent character.

Electronegativity

A measure of an atom's attraction for electrons on the Pauling scale.

Nonpolar covalent (EN Difference)

A classification of chemical bonds where the difference in electronegativity between bonded atoms is less than $0.5$.

Polar covalent (EN Difference)

A classification of chemical bonds where the difference in electronegativity between bonded atoms is between $0.5$ and $1.9$.

Ionic formation (EN Difference)

The process occurring when the difference in electronegativity between bonded atoms is greater than $1.9$, resulting in the transfer of electrons.

Bond dipole moment ($\mu$)

A measure of the polarity of a covalent bond calculated as the product of the charge on either atom times the distance between the two nuclei.

Electrostatic potential maps

Computer graphics used to identify sites of chemical reactivity by tracking overall molecular electron density distributions.

Octet rule

The tendency of atoms to interaction until they acquire a configuration with eight valence electrons, similar to the nearest noble gas.

Octet rule exceptions

Atoms such as Hydrogen ($2$ electrons), Boron and Aluminum (often $6$ electrons), and second-row elements like Phosphorus and Sulfur (can exceed $8$ electrons).

Resonance

A concept used when no single Lewis structure provides an accurate representation for a molecule or ion, requiring multiple contributing structures.

Curved arrow

A symbol used in organic chemistry to show the redistribution or movement of valence electrons; double-headed for two electrons and single-headed for one.

Hybridization

The mixing of atomic orbitals to create equivalent hybrid orbitals such as $sp^3$, $sp^2$, or $sp$.

$sp^{3}$ hybridization

The mixing of one $2s$ and three $2p$ orbitals to create four equivalent orbitals in a tetrahedral arrangement with bond angles of $109.5^\circ$.

$sp^{2}$ hybridization

The mixing of one $2s$ and two $2p$ orbitals to create three equivalent orbitals in a trigonal planar arrangement with bond angles of $120^\circ$, leaving one unhybridized $2p$ orbital.

$sp$ hybridization

The mixing of one $2s$ and one $2p$ orbital to create two equivalent orbitals in a linear arrangement with bond angles of $180^\circ$, leaving two unhybridized $2p$ orbitals.

Molecular Orbital (MO) Model

A model where orbitals in molecules arise from the combination of $n$ atomic orbitals to give $n$ molecular orbitals.

Bonding molecular orbital

A molecular orbital in which electrons have a lower energy than they would have in isolated atomic orbitals.

Antibonding molecular orbital

A molecular orbital in which electrons have a higher energy than they would have in isolated atomic orbitals.

Sigma ($\sigma$) bonding MO

A molecular orbital in which electron density is concentrated between two nuclei along the axis joining them.

Pi ($\pi$) bonding MO

A molecular orbital in which electron density lies above and below the internuclear axis.

Functional group

An atom or group of atoms within a molecule that shows a characteristic set of chemical reactivities and serves as the basis for naming organic compounds.

Alkane

A hydrocarbon consisting only of carbon-carbon single bonds.

Alkene

A hydrocarbon containing at least one carbon-carbon double bond.

Alkyne

A hydrocarbon containing at least one carbon-carbon triple bond.

Aromatic compound

A compound containing a benzene ring as its characteristic functional group.

Alkyl halide

A compound where a halogen atom ($F$, $Cl$, $Br$, or $I$) is single-bonded to a carbon atom.

Alcohol

A functional group containing a hydroxyl ($-OH$) group bonded to a carbon atom.

Ether

A functional group in which an oxygen atom is bonded to two carbon atoms ($R-O-R$).

Amine

A functional group containing a nitrogen atom bonded to one, two, or three carbon atoms by single bonds.

Thiol

A functional group containing a sulfhydryl ($-SH$) group.

Carbonyl group

A functional unit consisting of a carbon atom double-bonded to an oxygen atom ($C=O$).

Aldehyde

A compound containing a carbonyl group bonded to at least one hydrogen atom.

Ketone

A compound containing a carbonyl group bonded to two carbon groups.

Carboxylic acid

A compound containing a carboxyl ($-COOH$) group.

Ester

A derivative of a carboxylic acid in which the carboxyl hydrogen is replaced by a carbon group.

Amide

A derivative of a carboxylic acid in which the $-OH$ of the carboxyl group is replaced by an amine group.

Nitrile

A nitrogen-containing functional group characterized by a carbon-nitrogen triple bond ($C \equiv N$).

What are the steps to determine the most important resonance structure?

1.Structures where all atoms have filled valence shells (octets) contribute more than those with atoms with unfilled shells.
2. Structures with greater number of covalent bonds contribute more than those with fewer.
3. Structures without separation of unlike charges are more important than those with separation of charges.
4. Structures that place negative charge on more electronegative atom
and positive charge on less electronegative contribute more.