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Chapter 9 - Molecular Geometry and Bonding Theories
Vocabulary
29
Chemistry
Undergraduate 1
05/05/2010

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Term
Bond Angle
Definition
the angles (in degrees) defined by lines joining the enters of two atoms to a third atom to which they are covalently bonded
Term
Molecular Geometry
Definition
shape of the molecule; defined by the lowest energy arrangement of its atoms in three-dimensional space
Term
Valence Shell Electron-Pair Repulsion
VSEPR
Definition
predicts the arrangement of valence electron pairs around a central atoms that will minimize their mutual repulsion to produce the lower energy orientations
Term
Steric Number
Definition
the number of atoms bonded to the central atom plus the number of lone pairs of electrons on the central atom
Term
Linear
Definition
results when the bond angle between three atoms is 180
Term
Trigonal Planar
Definition
has a SN of 3 for the central atom of a molecule with no lone pairs and bond angles of 120
Term
Tetrahedral
Definition
has a SN of 4 for the central atom of a molecule with no lone pairs and bond angles of 109.5
Term
Trigonal Bipyramidal
Definition
has a SN of 5 for the central atom of a molecule with no lone pairs; three atoms occupy equatorial sites in the plane around the central atom with ideal bond angles of 120 and the other two atoms occupy axial sites above and below the central atom with a bond angle of 180
Term
Octahedral
Definition
has a SN of 6 for the central atom of a molecule with no lone pairs; all six sites are equivalent and the ideal bond angle for these atoms is 90
Term
Electron-Pair Geometry
Definition
describes the arrangement of atoms and lone pairs of electrons about a central atom
Term
Bond-Dipole
Definition
two covalently bonded atoms with different electonegativites have partial electrical charges of opposite sign
Term
Dipole Moment
Definition
a measured value that defines the extent of separation of positive and negative charge centers in a covalently bonded molecule; a quantitative expression of the polarity of a molecule
Term
Valence Bond Theory
Definition
assumes that covalent bonds form when orbitals on different atoms overlap or occupy the same region in space
Term
Sigma Bond
Definition
a covalent bond in which the highest electron density lies between the two atoms along the bond axis connecting them
Term
Hybridization
Definition
the mixing of atomic orbitals to generate new set of orbital that then are available to overlap and form covalent bonds with other atoms
Term
sp3 Hybrid Orbital
Definition
a tetrahedral orientation of valence electrons is achieved by forming four of these orbitals
Term
sp2 Hybrid Orbital
Definition
the trigonal planar orientation of valence electrons is achieved by this
Term
sp3d2 Hybrid Orbital
Definition
six of these orbitals point towards the vertices of an octahedron
Term
sp3d Hybrid Orbital
Definition
five of these orbitals have lobes that point toward the vertices of a trigonal bipyramid
Term
Pi Bond
Definition
electron density is greatest above and below or in front of an behind the bonding axis
Term
Delocalized
Definition
electrons in the pi bonds in a system with alternating single and double bonds can be this over several atoms or even an entire molecule
Term
Aromatic Compounds
Definition
molecules consisting of flat rings with pi electron cloud delocalized above and below the plan of molecules
Term
Molecular Orbital Theory
Definition
a 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
Term
Molecular Orbital
Definition
a regions of characteristic shape and energy where electrons in a molecule are located
Term
Antibonding Orbitals
Definition
destabilize the molecule because they do not increase the electron density between nuclear centers and therefore do not participate in holding the molecule together
Term
Sigma Molecular Orbital
Definition
when the region of highest density lies along the bond axis between two nuclear centers, electrons in sigmas orbitals form sigma bonds
Term
Molecular Orbital Diagram
Definition
energy level diagram; shows the relative energies and electron occupancy of the molecular orbitals for a molecule
Term
Diamagnetic
Definition
atoms, ions, and molecules have no unpaired electrons and are weakly repelled by a magnetic field
Term
Paramagnetic
Definition
atoms, ions, and molecule contain at least one unpaired electron and are attracted by an external magnetic field; the strength of the attraction increase as the number of unpaired electrons increases
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