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Types of bonding, what type of element they're between, and how e- react
- ionic (metals to nonmetals) - e- are transferred
- covalent (nonmetals to nonmetals) - e- are shared
- metallic (metal to metal) - e- are pooled
Bond type by electronegativitiy
- 0.0 = pure covalent
- 0.1 - 0.4 = nonpolar covalent
- 0.5 - 1.9 = polar covalent
- 2.0 - 4.0 = ionic
Octet rule exceptions
- H, He have only 2 e-
- Group IIIA elements may have 6 e- only
- Elements in period 3+ may have 8, 10, 12, or 14 e-
The only 3 free radical compounds (exceptions to lone pair rule)
NO, NO2, and ClO2
How do you check a Lewis Dot Diagram?
- Correct # of e-?
- Octet rule?
- Σ Formal Charges = charge of molecule?
Trends in bond length
- More e- shared by atoms = shorter covalent bond
- Bond length decreases from left to right across period
- Bond length increases down the column
Trends in bond energy (energy needed to break a bond)
- More e- shared by atoms = stronger covalent bond
- Shorter covalent bond = stronger covalent bond
Using bond energies to estimate ΔHrxn
ΔHrxn = ΣnΔH(bonds broken) - ΣnΔH(bonds formed)
Evaluating resonance structures
- Better structures have fewer formal charges
- Better structures have smaller formal charges
- Better structures have negative formal charges on more electronegative atoms
Possible shapes of molecules with VSEPR formula and bond angle
- AX2 - linear - 180˚
- AX3 - trigonal planar - 120˚
- AX2E - v shaped/bent
- AX4 - tetrahedral - 109.5˚
- AX3E - trigonal pyramidal
- AX2E2 - v shaped/bent
- AX5 - trigonal bipyramidal - 120˚ (equatorial) and 90˚ (axial to equatorial)
- AX4E - irregular tetrahedral / seesaw
- AX3E2 - T shaped
- AX2E3 - linear
- AX6 - octahedral - 90˚
- AX5E - square pyramidal
- AX4E2 - square planar
How do lone pairs affect bond angle?
Lone pair "take up more space" and decrease the bond angle between atoms
How to draw 3D object on 2D plane
- solid line - on the same plane as the paper
- solid bar - in front of plane
- dashed bar - behind plane
Which shapes result in non-polar molecules (through vector cancellation) and which shapes result in polar molecules (uncancelled vectors)?
- Nonpolar: linear, trigonal planar, tetrahedral, tigonal bipyramidal, octahedral, square planar
- Polar: bent, trigonal pyramidal, seesaw, t-shaped, square pyramidal
How does Valence bond theory explain bonding? List the hybrids, and their corelation to Lewis dot.
- VBR states that a bond is the overlap of atomic (or hybrid) orbitals.
- Hybrids are created based on the lewis dot structure, based on how many e- densitites the atom has.
- 2 (sp), 3 (sp2), 4 (sp3), 5 (sp3d), 6 (sp3d2)
How do you know how MANY hybrid orbitals to use?
- The number of atomic orbitals combined = the number of hybrids formed
- eg combining a 2s with a 2p gives 2 sp orbitals
Describe the different types of bonds using greek letters, and how each overlaps in depth.
- 1 single bond = 1 δ bond
- 1 double bond = 1 δ bond and 1 π bond
- 1 triple bond = 1 δ bond and 2 π bonds
- δ bonds overlap once, along the axis of the bond using hybrid orbitals
- π bonds overlap twice, perpendicular to axis using unhybridized p orbitals
Explain the steps in proving a hybridization
- Draw the lewis dot structure
- Get the electron configuration for the element
- Establish hybridization based on lewis dot
- Draw energy levels using electron configuration
- Create hybrids and fill in the electrons, make sure it matches (remember p orbitals are unhybridized in π bonds
How does Molecular orbit theory explain bonding?
Electrons belong to whole molecule, orbitals belong to whole molecule (delocalization)
Differences between VBT, MO, and Lewis
- VBT predicts many properties better than Lewis (bonding schemes, bond length, bond strengths, bond rigidity)
- VB presumes electrons are localized, and does not account for delocalization
- VB cannot predict perfectly (magnetic behavior)
- MO can predict bond order, energies, magnetic properties
- Both are used, but have strengths and weaknesses
What forms a bonding molecular orbital? What are the symbols?
- When the two wave functions combine constructively the resulting molecular orbital has less energy than the original atomic orbital
- δ and π are bonding orbitals (most electon density between nuclei)
What forms a antibonding molecular orbital? What are the symbols?
- When the two wave functions combine deconstructively the resulting molecular orbital has more energy than the original atomic orbitals
- δ* and π* are antibonding orbitals (most electon density outside nuclei)
- nodes (spaces without electrons) between nuclei
What is bond order?
- (Bonding electrons - antibonding electrons) / 2
- Only use valence electrons
- higher bond order = stronger/shorter bonds
- fractions possible
MO paramagnetic vs diamagnetic
- paramagnetic (attracted to magnets) if MO diagram has unpared electrons
- diamagnetic (not attracted to magnets) if MO diagram has all electrons paired
LUMO, HOMO, and what they are used for.
- Lowest Unpaired Molecular Orbit
- Highest Occupied Molecular Orbit
- Difference is used to determine wavelength absorpotion by molecule
Name of structure that ions form?
What is lattice energy (ΔHlattice)? Formulaic definition? What formula/factors affect lattice energy?
- Energy released when 1 mol solid crystal forms from ions in gas state
- ΔHlattice = cation(g) + anion(g) -> 1 mol molecule(s)
- Always exothermic
- Depends on size/charge of ions [direct] and distance between ions [inverse]
- E = C x q1q2/r
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