Chapter 5 - Bonding Theories: Explaining Molecular Geometry

Optical isomers

Optical isomers

________: stereoisomers that can rotate plane polarized light (electric fields oscillating in one plane) are optically active.

Repulsion

________ is minimized when distance is maximized.

Paramagnetic

________: substance is attracted by a magnetic field, increases as amount of unpaired electrons increases.

Conjugation

________: alternating single and multiple bonds in molecular compounds in which adjacent atoms have unhybridized p orbitals.

Diasteromers

________: stereoisomers that are not enantiomers.

High energy

________ is designated π*,* electrons occupying π* detract from π bond formation.

VESPR

________ is based on the principle that electrons have negative charges and repel each other and applies that idea by assuming that valence electrons are arranged around central atoms to minimize repulsions.

Intercalation

________: when polycyclic aromatic hydrocarbons (PAH) bind to cellular DNA.

Trigonal Bipyramidal

________: SN= 5, bond angles between equatorial are 120, angle between equatorial and axial bond is 90 and the bond between the two axial is 180.

Electrons

________ can undergo absorption and emission.

Trigonal planar

________: SN= 3, three bonding atoms are as far apart as possible, bond angle is 120.

Trigonal Pyramidal

________: SN= 4 (3 bonds, one lone pair) with an angle of 107.

Isomers

________: compounds with the same chemical formula but different molecular structures.

Lewis

________ structures account for the bonding in molecules and polyatomic ions- they show what atoms are connected but they dont show how the atoms are oriented in three dimensions or the overall shape.

Stereoisomers

________: identical lewis structures but three dimensional bonds /orientations are not the same.

Hybridization

________: mixing of atomic orbitals to generate new sets of orbitals that may form sigma bonds with other atoms.

Diamagnetic

________: substances are repelled slightly by a magnetic field.

lone pairs

Linear: SN= 5 (2 bonds, 3 ________) has an angle of <180.

Enantiomers

________: same composition, bonds but different three- dimensional shapes; nonsuperimposable mirror images.

Sigma molecular orbital

________: oval shaped and spans two atomic center, two electrons create a single σ bond.

Square Pyramidal

________: SN= 6 (5 bonds, 1 lone pair) has an angle of <90.

Square Planar

________: SN= 6 (4 bonds, 2 lone pairs) has an angle of 90.

Chirality

________: also known as stereocenter, contains 1+ chiral atoms, determined by the presence of any sp3 carbon groups bonded to four different atoms or groups of atoms.

Electron pair

________ geometry: relative positions in 3- D space of all bonding and lone pairs of valence electrons.

lone pair

Seesaw: SN= 5 (4 bonds, one ________) has an angle of <90, <120.

Repulsion

________ between lone pairs and bonding pairs is greater than ________ between bonding pairs.

lone pairs

T- shaped: SN= 5 (3 bonds, 2 ________) has an angle of <90.

Repulsion

________ caused by a double bond is greater than ________ caused by a single bond.

Repulsion

________ caused by lone pair is greater than ________ caused by double bond.

Lewis structures account for the bonding in molecules and polyatomic ions

they show what atoms are connected but they dont show how the atoms are oriented in three dimensions or the overall shape

Bond angle

the angle in degrees defined by lines joining the centers of two atoms to a third atom to which they are chemically bonded

Electron-pair geometry

relative positions in 3-D space of all bonding and lone pairs of valence electrons

Molecular geometry

relative positions of atoms in a molecule

Steric Number (SN)

is the sum of the number of atoms bonded to that atom and the number of lone pairs on it

Linear pair

SN=2, three atoms in a straight line, angle between two bonds is 180

Trigonal planar

SN=3, three bonding atoms are as far apart as possible, bond angle is 120

Tetrahedral

SN=4, four bonding pairs form angles of 109.5

Trigonal Bipyramidal

SN=5, bond angles between equatorial are 120, angle between equatorial and axial bond is 90 and the bond between the two axial is 180

Octahedral

SN=6, two pairs in each set are 180 to each other and 90 to the other two pairs

Angular or Bent

SN=3 (two bonds, one lone pair) with a bond angle of 117

Trigonal Pyramidal

SN=4 (3 bonds, one lone pair) with an angle of 107

Seesaw

SN=5 (4 bonds, one lone pair) has an angle of <90, <120

T-shaped

SN=5 (3 bonds, 2 lone pairs) has an angle of <90

Linear

SN=5 (2 bonds, 3 lone pairs) has an angle of <180

Square Pyramidal

SN=6 (5 bonds, 1 lone pair) has an angle of <90

Square Planar

SN=6 (4 bonds, 2 lone pairs) has an angle of 90

Bond Dipole

separation of charge caused by the electronegativity difference between two atoms

Permanent Dipole

the permanent separation of charge in a molecule resulting from unequal distributions of bonding and/or lone pairs

Valence bond theory

evolved in 1920s when Pauling merged quantum mechanics with Lewis model; states that a chemical bond forms when the atomic orbitals of two atoms overlap and are then attracted to the nuclei of both bonded atoms, lowering potential energy and greater stability

Sigma Bond

a covalent bond in which the highest electron density resides between two atoms along the internuclear axis

Pi Bond

covalent bond in which electron densities are highest above and below the internuclear axis; one bond formed through two points of contact

Hybridization

mixing of atomic orbitals to generate new sets of orbitals that may form sigma bonds with other atoms

Molecular Recognition

process by which molecules interact with receptors or active sites in your tissues, usually does not involve forming covalent bonds

Conjugation

alternating single and multiple bonds in molecular compounds in which adjacent atoms have unhybridized p orbitals

Intercalation

when polycyclic aromatic hydrocarbons (PAH) bind to cellular DNA

Isomers

compounds with the same chemical formula but different molecular structures

stereoisomers

identical lewis structures but three dimensional bonds/orientations are not the same

enantiomers

same composition, bonds but different three-dimensional shapes; nonsuperimposable mirror images

diasteromers

stereoisomers that are not enantiomers

optical isomers

stereoisomers that can rotate plane polarized light (electric fields oscillating in one plane) are optically active

Chirality

also known as stereocenter, contains 1+ chiral atoms, determined by the presence of any sp3 carbon groups bonded to four different atoms or groups of atoms

Molecular Orbital Theory

bonding theory based on the mixing of atomic orbitals of similar shapes and energies to form molecular orbitals that belong to the molecule as a whole; total number of molecular orbitals must match the number of atomic orbitals involved in forming them

bonding orbitals

lobes of high electron density that lie between bonded pairs of atoms, lower energies than the atomic orbitals that combined to form them; closer in energy to atomic orbitals of more electronegative atom

antibonding orbitals

lobes of high electron density not located between bonding atoms, higher energies than the atomic orbitals that combined to form them; closer in energy to atomic orbitals of less electronegative atom

Sigma molecular orbital

oval shaped and spans two atomic center, two electrons create a single σ bond

Pi molecular orbital

mixing of molecular orbitals oriented above/below or front/behind internuclear axis

Diamagnetic

substances are repelled slightly by a magnetic field

Paramagnetic

substance is attracted by a magnetic field, increases as amount of unpaired electrons increases