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Chapter 10

Chem Bond 2: Molecular Shapes, Valence Bond Theory, and Molecular Orbital Theory

TermDefinition
Valence Shell Electron Pair Repulsion(VESPR) Theory Electron groups repel one another through couloumbic forces. The repulsions between electron groups on interior atoms of a molecule determine the geometry of the molecule
Electron Groups Lone pairs, single bonds, multiple bonds, and even single electrons
Linear Geometry Central atom has two electron groups. 2D. The molecular geometry of three atoms with a bond angle of 180 degrees due to the repulsion of two electron groups. Ex: BeCl2 and CO2
Trigonal Planar Geometry Central atom has three electron groups. 2D.The molecular geometry of four atoms with bond angles of 120 degrees in a plane. Ex: BF3
Tetrahedral Geometry Central atom has four electron groups. 3D. The molecular geometry of five atoms with bond angles of 109.5 degrees. Ex: CH4
Trigonal Bypyrimidal Central atom has five electron groups. 3D. The molecular geometry of six atoms with bond angles of 120 degrees between the three equatorial electron group and bond angles of 90 degrees between the two axial electron groups and the trigonal plane. Ex: PCl5
Octahedral Geometry Central atom has six electron groups. 3D. The molecular geometry of seven atoms with all 90 degree angles. Ex: SF6
Electron Geometry The geometrical arrangement of the electron groups
Molecular Geometry The geometrical arrangement of the atoms
Bent When a central atom has four electron groups(two bonding pairs and two lone pairs), its electro geometry is also tetrahedral, but its molecular geometry is bent. Bond angles smaller than 109.5 degrees. Bond angles are 104.5 degrees. Ex: H2O
Electron Group Repulsion Level Lone pair - Lone pair > Lone pair - Bonding pair > Bonding pair - Bonding pair
Seesaw The molecular geometry of a molecule with trigonal bypyrimidal electron geometry and on lone pair in an axial position. Resembles a seesaw. Ex: SF4
T-Shaped The molecular geometry of a molecule with trigonal bypyrimidal electron geometry and two lone pairs in axial position. Ex: BrF3
Square Pyramidal The molecular geometry of a molecule with octahedral electron geometry and one lone pair. Two of the six electron groups around the central are lone pairs. Ex: XeF4
1, Summarizing VESPR Theory The geometry of a molecule is determined by the number of electron groups on the central atom(or on all interior atoms, if there is more than one)
2, Summarizing VESPR Theory The number of electron groups is determined from the Lewis structure of the molecule. If the Lewis structure contains resonance structures, use any one of the resonance structure to determine the number of electron group
3, Summarizing VESPR Theory Each of the following counts as a single electron group: a lone pair, a single bond, a double bond, a triple bond, or a single electron(as in a free radical)
4, Summarizing VESPR Theory The geometry of the electron group is determined by their repulsions. In general, electron group repulsions vary as follows... Lone pair - lone pair > lone pair - bonding pair > bonding pair - bonding pair
5, Summarizing VESPR Theory Bond angles can vary from the idealized angles becuase double and triple bonds occupy more space than single bonds(they are bulkier even though they are shorter), and lone pairs occupy more space than bonding groups.
6.Summarizing VESPR Theory The presence of lone pairs usually makes bond anlges smaller than the ideal angle for the particular geometry
Steps for Predicting Molecular Geometries 1. Draw Lewis Structure of molecule.. 2. Determine total # electron groups around central atom.. 3. Determine # bonding groups and # lone pairs around central atom.. 4. Refer to table 10.1 to determine the electron geometry and molecular geometry
Straight Line For Drawing Molecules Bond in plane of paper
Hatched Wedge For Drawing Molecules Bond going into the page
Solid Wedge For Drawing Molecules Bond coming out of the page
Summarizing Molecular Shape and Polarity 1. Draw the Lewis structure for the molecule and determine its molecular geomtetry.. 2. Determine if the molecule contains polar bonds.. 3. Determine if the polar bonds add together to form a net dipole moment
Valence Bond Theory An advanced model of chemcial bonding in which electron reside in quantum-mechanical orbitals localized on individual atoms that are a hybridized blend of standard atomic orbitals; chemical bonds result from an overlap of these orbitals
Hybridized Atomic Orbitals A kind of blend or combination of two or more standard atomic orbitals
Hybridization A mathematical procedure in which the stardard atomic orbitals are combined to form new atomic orbitals, hybrid orbitals
Hybrid Orbitals Orbitals formed from the combination of standard atomic orbitals that correspond more closely to the actual distribution of electron in a chemically bonded atom
1st General Statement Regarding Hybridization The number of standard atomic orbitals added together always equals the number of hybrid orbitals formed. The total number of orbitals is conserved
2nd General Statement Regarding Hybridization The particular combinations of standard atomic orbitals added together determines the shape and energies of hybrid orbitals formed
3rd General Statement Regarding Hybridization The particular type of hybridization that occurs is the one that yields the lowest overall energy for the molecule
Pi(π) Bond Forms when orbitals overlap side by side
Sigma(σ) Bond Forms when orbitals overlap end-to-end
Single Bond Consists of a sigma bond
Double Bond Consists of a sigma bond and a pi bond
Triple Bond Consists of a sigma bond and 2 pi bonds
Molecular Geometries that Are Always Polar 1. Bent 109 degrees.. 2. Bent 120 degrees.. 3. Trigonal Pyramid.. 4. Seesaw.. 5. T-shaped.. 6. Square Pyramid.. All pyramid, all bent, t-shaped, and seesaw
Molecular Orbital Theory An advanced model of chemical bonding in which electrons reside in molecular orbitals delocalized over the entire molecule. In the simplest version, the molecular orbitals are simply linear combinations of atomic orbitals
Bonding Orbital A molecular orbital that is lower in energy than any of the atomic orbitals from which it was formed
1. Hybridization Scheme from Electron Geometry 1. #E Groups(2)..E Geom(Linear)..Hybridization Scheme(sp)... 2. #E Groups(3)..E Geom(Trigonal Planar)..Hybridization Scheme(sp^2)... 3. #E Groups(4)..E Geom(Tetrahedral)..Hybridization Scheme(sp^3)
2. Hybridization Scheme from Electron Geometry 4. #E Groups(5)..E Geom(Trigonal Bypyramidal)..Hybridization Scheme(sp^3d)... 5. #E Groups(6)..E Geom(Octahedral)..Hybridization Scheme(sp^3d^2)...
Antibonding Orbital A molecular orbital that is higher in energy than any of the atomic orbital from which it was formed. Tend to raise the energy of the system(relative to the unbonded atoms)
Bond Order For a molecule, the number of bonds divided by the number of atoms bonded to that atom.
Types of Intermolecular Forces 1. Dispersion(London Forces, van der Waals force).. 2. Dipole - dipole.. 3. Hydrogen bonding.. 4. Ion - dipole
Dispersion(London forces) Present in all molecules and atoms
Dipole - Dipole Present in polar molecules
Hydrogen Bonding Present in molecules containing H bonded to F, O, or N
Ion - Dipole Present in mixtures of ionic compounds and polar compounds
Strength of Intermolecular Forces from Least to Greatest Dispersion < Dipole-dipole < Hydrogen bonding < Ion-dipole
Created by: TimChemistry1