Chemistry Quiz 1
Hybridization facts:
1. A linear electron geometry corresponds to sp hybridization. 2. A trigonal planar geometry corresponds to sp2 hybridization. 3. A tetrahedral geometry corresponds to a sp3 hybridization. 4. A trigonal bipyramidal geometry corresponds to a sp3d hybridization. 5. An octahedral geometry corresponds to a sp3d2 hybridization.
What are the five basic electron geometries? State the number of electron groups corresponding to each.
1. Linear- two electron groups. 2. Trigonal Planar- three electron groups. 3. Tetrahedral- four electron groups. 4. Trigonal Bipyramidal- five electron 5. Octahedral- six electron groups.
Here are just a few examples of some funky molecular geometries based on the presence of electron groups around the central atom :)))))))
1. Trigonal Pyramidal- four electron groups: 3 bonding, 1 lone pair 2. Bent: 4 electron groups: 2 bonding, 2 lone pairs 3. Seesaw- 5 electron groups: 4 bonding groups, 1 lone pair 4. T Shaped- 5 electron groups; 3 bonding, 2 lone pairs 5. Linear- 5 electron groups: 2 bonding, 3 lone pairs 6. Square pyramidal- 6 electron groups: 5 bonding, 1 lone pair 7. Square planar- 6 electron groups: 4 bonding, 2 lone pais
What is an antibonding molecular orbital?
An antibonding molecular orbital is higher in energy than the atomic orbitals for which it was formed. There is less electron density in the internuclear region which results in a node.
continued.... MOLECULAR ORBITAL THEORY
An even more complex quantum-mechanical model is molecular orbital theory. In molecular orbital theory, a chemical bond occurs when the electrons in the atom can lower their energy by occupying the molecular orbitals of the resultant molecule. The chemical bonds in MO theory are not localized between atoms, but spread throughout the entire molecule. Molecular orbital theory uses trial functions to solve the Schrödinger equation for the molecules. To determine how well the trial function works, you calculate the energy, trying to minimize the energy. However, no matter how "good" you guess, you can never do better than nature at minimizing energy. These minimum-energy calculations for orbitals must be done by computer.
In molecular orbital theory, what is a nonbonding orbital?
Nonbonding orbitals are atomic orbitals not involved in a bond that remain localized on the atom.
Why is polarity important?
Polarity is important because polar and nonpolar molecules have different properties. Polar molecules interact strongly with other polar molecules, but do not interact with nonpolar and vice versa.
Why does the energy ordering of the molecular orbitals of the period 2 diatomic molecules change in going from N2 to O2?
The degree of mixing between two orbitals decreases with increasing energy difference between them. Mixing of the 2s and 2px orbitals is greater in B2, C2 and N2 than in O2, F2, and Ne2 because in B, C, and N, the energy levels of the atomic orbitals are more closely spaced than in O, F, and Ne. This mixing produces a change in energy ordering for the pi 2p and sigma 2p molecular orbitals.
In the Lewis model, the 2 bonds in a double bond look identical. However, valence bond theory shows that they are not. Describe a double bond according to valence bond theory. Explain why rotation is restricted with a double bond but not a single bond.
The double bond in Lewis Theory is simply two pairs of electrons that are shared between the same two atoms. However, in valence bond theory we see that the double bond is made up of two different kinds of bonds- one pi and one sigma. Valence bond theory shows that rotation about a double bond is severely restricted. Because of the side-by-side overlap of the p orbitals, the pi bond must essentially break for rotation to occur. The sigma bond consists of end to end overlap. Because the overlap is linear, rotation is not restricted.
What constitutes an electron group?
An electron group is defined as a lone pair of electrons, a single bond, a multiple bond, or even a single electron.
In molecular orbital theory, what is bond order? Why is it important?
BO in a diatomic molecule= (# bonding electrons - # antibonding electrons)/ 2. The higher the bond order, the stronger the bond. A negative or zero bond order indicates that a bond will not form between the atoms.
Be able to sketch all five different hybrid orbitals.
Bond Angles: sp: 180 sp2: 120 sp3: 109.5 sp3d: 90 and 120 sp3d2: 90 https://socratic.org/questions/what-are-the-steps-associated-with-the-process-of-constructing-a-hybrid-orbital- https://socratic.org/questions/what-are-the-steps-associated-with-the-process-of-constructing-a-hybrid-orbital-
continued.... Flaws of Valence Bond Theory
However, valence bond theory falls short in explaining certain phenomenon, such as magnetism, and certain bond properties. Valence bond theory treats the electrons as if they reside in the quantum-mechanical orbitals we calculate for an atom. This is an oversimplification that is partially compensated for by the concept of hybridization.
How does hybridization of the atomic orbitals in the central atom of a molecule help lower the overall energy of the molecule?
Hybrid orbitals minimize the energy of the molecule by maximizing the orbital overlap in a bond.
What is hybridization? Why is hybridization necessary in valence bond theory?
Hybridization is a mathematical procedure in which the standard atomic orbitals are combined to form new atomic orbitals called hybrid orbitals. Hybrid orbitals are still localized on individual atoms, but they have different shapes and energies from those of standard atomic orbitals. Hybrid orbitals are necessary to valence bond theory because they correspond more closely to the actual distribution of electrons in chemically bonded atoms.
Summarize the three different models for representing molecules. LEWIS THEORY
In Lewis theory, a chemical bond is the transfer or sharing of electrons represented as dots. Lewis theory allows us to predict the combination of atoms that form stable molecules and the general shape of a molecule. Lewis theory is a quick way to predict the stability and shapes of molecules based on the number of valence electrons. However, it does not deal with how the bonds that we make are formed.
What is a chemical bond according to molecular orbital theory?
In molecular orbital theory, atoms will bond when the electrons in the atoms can lower their energy by occupying the molecular orbitals of the resultant molecule.
Explain the difference between hybrid atomic orbitals in valence bond theory and LCAO (linear combination of atomic orbitals) molecular orbitals in molecular orbital theory.
In valence bond theory, hybrid orbitals are weighted linear sums of the valence atomic orbitals of a particular atom, and the hybrid orbitals remain localized on that atom. In molecular orbital theory, the molecular orbitals are weighted linear sums of the valence atomic orbitals of all the atoms in a molecule, and many of the molecular orbitals are delocalized over the entire molecule.
Fact about valence bond theory
In valence bond theory, the interaction energy between the electrons and nucleus of one atom with the electrons and nucleus of another atom is usually negative (stabilizing) when the interacting atomic orbitals contain a total of 2 electrons that can spin pair.
How do you apply VSEPR theory to predict the shape of molecules with more than one interior atom?
Larger molecules may have two or more interior atoms. When predicting the shapes of these molecules, determine the geometry about each interior atom and use these geometries to determine the geometry about each inerior atom and use these geometries to determine the entire three-dimensional shape of the molecule.
Be able to sketch the molecular orbitals for bonding and antibonding sigma and pi 2s and 2p
Look it up :))))))
How is the number of molecular orbitals approximated by a linear combination of atomic orbitals related to the number of atomic orbitals used in approximation?
Molecular orbitals can be approximated by a linear combination of atomic orbitals. The total number of molecular orbitals formed from a particular set of atomic orbitals will always equal the number of atomic orbitals used.
Be able to draw an energy diagram for the molecular orbitals for period 2 diatomic molecules. Show the difference in ordering for B2, C2, and N2, when compared to O2, F2, and Ne2.
https://www.google.com/search?q=energy+diagrams+for+period+2+diatomic+molecules&rlz=1C5CHFA_enUS696US696&espv=2&biw=1440&bih=826&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjk8tPJgtnRAhXk34MKHY1zDAkQ_AUIBigB#imgrc=xEYehQe-PqPi3M%3A
In valence bond theory, what determines the geometry of the molecule?
According to valence bond theory, the shape of the molecule is determined by the geometry of the overlapping orbitals.
What is a bonding molecular orbital?
A bonding molecular orbital is lower in energy than the atomic orbitals from which it is formed. There is an increased electron density in the internuclear region.
Explain the difference between a paramagnetic species and a diamagnetic species.
A paramagnetic species has unpaired electrons in one or more molecular orbitals. A paramagnetic species is attracted to a magnetic field. The magnetic property is a result of the unpaired electrons. The spin and angular momentum of the electrons generate tiny magnetic fields. F Diamagnetic species have all electrons paired. The magnetic field caused by the electron spin and angular momentum tend to cancel each other out. A diamagnetic species is not attracted to a magnetic field and is in fact slightly repelled.
What is a chemical bond according to valence bond theory?
According to valence bond theory, a chemical bond results from the overlap of 2 half-filled orbitals with spin pairing of the two valence electrons.
Explain the difference between electron geometry and molecular geometry. Under what circumstances are they not the same?
The electron geometry is the geometrical arrangement of the electron groups around the central atom. The molecular geometry is the geometrical arrangement of the atoms around the central atoms. The electron geometry and the molecular geometry are the same when every electron group bonds two atoms together. The presence of unbonded lone pair electrons gives a different molecular geometry and electron geometry.
What is the role of wave interference in determining whether a molecular orbital is bonding or antibonding?
The electrons in orbitals behave like waves. The bonding molecular orbital arises from the constructive interference between the atomic orbitals is lower in energy than the atomic orbitals. The antibonding molecular orbital arises from the destructive interference between the atomic orbitals and is higher in energy than the atomic orbitals.
How is the number of hybrid orbitals related to the number of standard atomic orbitals that are hybridized?
The number of standard atomic orbitals added together always equals the number of hybrid orbitals formed. The total number of orbitals is conserved.
Why is molecular geometry important? Cite some examples.
The properties of molecules are directly related to their shapes. The sensation of taste, immune response, the sense of smell and many types of drug action all depend on shape-specific interactions between molecules and proteins.
According to VSEPR theory, what determines the geometry of a molecule?
The repulsion between electron groups on interior atoms of a molecule determines the geometry of the molecule.
How do you determine whether a molecule is polar?
To determine if a molecule is polar, do the following: 1. Draw the Lewis structure for the molecule and determine the molecular geometry. 2. Determine whether the molecule contains polar bonds (If the difference in electronegativity for the atoms in a bond is greater than 0.4, we consider the bond polar. If the difference in electronegativity is less than 0.4, the bond is essentially nonpolar). 3. Determine whether the polar bonds add together to form a net dipole moment.
continued... VALENCE BOND THEORY
Valence bond theory is a more advanced bonding theory that treats electrons in a quantum-mechanical manner. A quantitative approach is extremely complicated, but a qualitative approach allows an understanding of how the bonds are formed. In valence bond theory, electrons reside in quantum-mechanical orbitals localized on individual atoms. When two atoms approach each other, the electrons and nucleus of one atom interact with the electron and nucleus of the other atom. If the energy of the system is lowered, a chemical bond forms. So valence bond theory portrays a chemical bond as the overlap of two half-filled atomic orbitals. The shape of the molecule can be predicted from the geometry of the overlapping orbitals. Also, valence bond theory explains the rigidity of the double bond.
When applying molecular orbital theory to heteronuclear diatomic molecules, the atomic orbitals used may be of different energies. If two atomic orbitals of different energies make two molecular orbitals, how are the energies of the molecular orbitals related to the energies of the atomic orbitals? How is the shape of the resultant molecular orbitals related to the shape of the atomic orbitals?
When two atomic orbitals are different, the weighting of each orbital in forming a molecular orbital may be different. When a molecular orbital is approximated as a linear combination of atomic orbitals of different energies, the lower atomic orbital makes a greater contribution to the antibonding molecular orbital. The shape of the molecular orbital shows a greater electron density at the atom that has the lower atomic orbital energy.
