[VOCAB] Chapter 10: The Shapes of Molecules

Question 1

Axial Group

Answer 1

An atom (or group) that lies above or below the trigonal plane of a trigonal bipyramidal molecule, or a similar structural feature in a molecule

Question 2

Bent

Answer 2

(also V-shaped) A molecular shape that arises when a central atom is bonded to two other atoms and has one or two lone pairs; occurs as the AX2E shape class (bond angle < 120°) in the trigonal planar arrangement and as the AX2E2 shape class (bond angle < 109.5°) in the tetrahedral arrangement

Question 3

Bond Angle

Answer 3

The angle formed by the bonds joining the nuclei of two surrounding atoms to the nucleus of the central atom, which is at the vertex

Question 4

Dipole Moment (μ)

Answer 4

A measure of molecular polarity; the magnitude of the partial charges on the ends of a molecule (in coulombs) times the distance between them (in meters)

Question 5

Electron Deficient

Answer 5

Referring to a bonded atom, such as Be or B, that has fewer than eight valence electrons

Question 6

Electron-Pair Delocalization

Answer 6

(also delocalization) The process by which electron density is spread over several atoms rather than remaining between two

Question 7

Equatorial Group

Answer 7

An atom (or group) that lies in the trigonal plane of a trigonal bipyramidal molecule, or a similar structural feature in a molecule

Question 8

Expanded Valence Shell

Answer 8

A valence level that can accommodate more than eight electrons by using available d orbitals; occurs only with central nonmetal atoms from Period 3 or higher

Question 9

Formal Charge

Answer 9

The hypothetical charge on an atom in a molecule or an ion, equal to the number of valence electrons minus the sum of all the unshared and half the shared valence electrons

Question 10

Free Radical

Answer 10

A molecular or atomic species with one or more unpaired electrons, which typically make it very reactive

Question 11

Lewis Structure

Answer 11

(also Lewis formula) A structural formula consisting of electron-dot symbols, with lines as bonding pairs and dots as lone pairs

Question 12

Linear Arrangement

Answer 12

The geometric arrangement obtained when two electron groups maximize their separation around a central atom

Question 13

Linear Shape

Answer 13

A molecular shape formed by three atoms lying in a straight line, with a bond angle of 180° (shape class AX2 or AX2E3)

Question 14

Molecular Polarity

Answer 14

The overall distribution of electronic charge in a molecule, determined by its shape and bond polarities

Question 15

Molecular Shape

Answer 15

The three-dimensional arrangement of the atomic nuclei in a molecule

Question 16

Octahedral Arrangement

Answer 16

The geometric arrangement obtained when six electron groups maximize their space around a central atom; when all six groups are bonding groups, the molecular shape is octahedral (AX6; ideal bond angle = 90°)

Question 17

Resonance Hybrid

Answer 17

The weighted average of the resonance structures for a species

Question 18

Resonance Structure

Answer 18

(also resonance form) One of two or more Lewis structures for a species that cannot be adequately depicted by a single structure. Resonance structures differ only in the position of bonding and lone electron pairs

Question 19

Seesaw Shape

Answer 19

A molecular shape caused by the presence of one equatorial lone pair in a trigonal bipyramidal arrangement (AX4E)

Question 20

Square Planar Shape

Answer 20

A molecular shape (AX4E2) caused by the presence of two lone pairs at opposite vertices in an octahedral electron-group arrangement

Question 21

Square Pyramidal Shape

Answer 21

A molecular shape (AX5E) caused by the presence of one lone pair in an octahedral electron-group arrangement

Question 22

T-shaped

Answer 22

A molecular shape caused by the presence of two equatorial lone pairs in a trigonal bipyramidal arrangement (AX3E2)

Question 23

Tetrahedral Arrangement

Answer 23

The geometric arrangement formed when four electron groups maximize their separation around a central atom; when all four groups are bonding groups, the molecular shape is tetrahedral (AX4; ideal bond angle 109.5°)

Question 24

Trigonal Bipyramidal Arrangement

Answer 24

The geometric arrangement formed when five electron groups maximize their separation around a central atom. When all five groups are bonding groups, the molecular shape is trigonal bipyramidal (AX5; ideal bond angles, axial-center-equatorial 90° and equatorial-center-equatorial 120°)

Question 25

Trigonal Planar Arrangement

Answer 25

The geometric arrangement formed when three electron groups maximize their separation around a central atom. When all three groups are bonding groups, the molecular shape is trigonal planar (AX3; ideal bond angle 120°)

Question 26

Trigonal Pyramidal Shape

Answer 26

A molecular shape (AX3E) caused by the presence of one lone pair in a tetrahedral arrangement

Question 27

Valence-Shell Electron-Pair Repulsion (VSEPR) Theory

Answer 27

A model explaining that the shapes of molecules and ions result from minimizing electron-pair repulsions around a central atom