EXAM 2: 08 Molecules In 3d Flashcards
Electron domains are distributed around central atoms to minimize…
Electron-pair repulsion
What is the Valence Shell Electron Pair Repulsion model (VSEPR)
A model to represent the arrangement of atoms so that electron pairs are as far from each other as possible
What is the bond angle and shape name for AX2
180 angle
Linear shape
What is the bond angle and shape name of AX3 (three bonding partners)
Trigonal Planar geometry
120 angles
What is the bond angle and shape for AX4 (four bonding partners)
Tetrahedral
109.5 angle
What is the bond angle and shape of AX5
Trigonal bipyramid
120 angles between equatorial bonds
90 angles between any pair of equatorial and axial bonds
What is an equatorial bond
The three bonds that are arranged in a trigonal plane in a trigonal bipyramidal geometry
What is an axial bond
Two bonds that form an axis perpendicular to the trigonal plane
- pointing toward the apexes of the pyramids
What is the bond angle and shape name of AX6
Octahedron
Bond angles are 90 or 180
What do canonical structures represent
The optimal possible spatial arrangement of atoms bonded to the central atom
What is steric number
The number of electron domains around any central atom
What is the difference between electron-domain geometry and molecular geometry
Electron geometry is the arrangement and number of electron groups while molecular geometry depends on the number of electron groups and the number of lone pairs
- molecular geometry is more specific
What is the molecular geometry of a molecule with a steric number of 2 and zero lone pairs
Linear
What is the molecular geometry of a molecule with a steric number of 3 and zero lone pairs
Trigonal planar
What is the molecular geometry of a molecule with a steric number of 3 and one being a lone pair
Bent
What is the molecular geometry of a molecule with a steric number of 4 with zero lone pairs
Tetrahedral
What is the molecular geometry of a molecule with a steric number of 4, one being a lone pair
Trigonal pyramidal
What is the molecular geometry of a molecule with a steric number of 4, two being lone pairs
Bent
What is the molecular geometry of a molecule with a steric number of 5 and zero lone pairs
Trigonal bipyramidal
What is the molecular geometry of a molecule with a steric number of 5, one being a lone pair
Seesaw
What is the molecular geometry of a molecule with a steric number of 5 and two lone pairs
T-shape
What is the molecular geometry of a molecule with a steric number of 5 and three lone pairs
Linear
What is the molecular geometry of a molecule with a steric number of 6 and zero lone pairs
Octahedral
What is the molecular geometry of a molecule with a steric number of 6 and one lone pairs
Square pyramidal
What is the molecular geometry of a molecule with a steric number of 6 and two lone pairs
Square planar
What tells us the electron domain geometry
The steric number
Only 5 options: linear, trigonal planar, tetrahedral, trigonal bipyramidal or octahedral
What does the molecular geometry depend on
The number of nonbonding pairs
(Cannot determine bond angles for lone pairs)
Molecules with a steric number of 3 can have what molecular geometries
Trigonal planar or bent
Molecules with a steric number of 4 can have molecular geometries of
Tetrahedral, trigonal pyramidal, or bent
What are the possible molecular geometries of molecules with a steric number of 5
Trigonal bipyramidal, seesaw, t-shaped, or linear
Are nonbonding domains more or less repulsive than bonding domains
More repulsive
What are the possible molecular geometries of molecules with a steric number of 6
Octahedral, square pyramidal or square planar
Is the repulsion caused by lone pair electron domains greater or less than the repulsion caused by multiple bond domains
Greater
Are multiple bonds more or less repulsive than single bonds
Somewhat more repulsive, although less than lone pair
Molecules with a steric number or 3 have bond angles close to the canonical angle of…
120
Molecules with a steric number of 4 have bond angles close to the canonical angle of…
109.5
Molecules with a steric number of 5 have bond angles close to the canonical angles of…
90 and 120
Molecules with a steric number of 6 have bond angles near the canonical angle of..
90
Molecules are polar if..
They have polar bonds and a geometry such that their bond dipoles do not cancel each other out
What are the two conditions that have to be satisfied for a molecule to show a net dipole moment
- The molecule has to have polar bonds, i.e. bonds between atoms of differing electronegativity. The larger the electronegativity difference, the bigger the magnitude of the resulting bond dipoles.
- The bond dipoles must not cancel. The bond dipole moments are vectors that have magnitude and direction. The magnitude of the vectors is dictated by the electronegativity differences between bonded atoms. The relative spatial positions of the vectors and their orientation (the direction they points in) is determined by the 3d shape of the molecule
Symmetrical molecules with identical atoms bonded to the central atom have ____ net dipole moments, even if they have polar bonds
NO!
What shapes are symmetrical molecules where the bond dipoles cancel and the net dipole is zero
Linear, octahedral, square planar, trigonal planar and tetrahedral
Along the lone pair axis, where are dipole moment vectors pointing
Away from the nucleus
Usually small contributions
Molecular dipole moments are..
Vector sums of bond dipoles
