Gen Chem I Exam # 3

Which of the following statements are true? Check all that apply. -The average speed of gas molecules decreases with decreasing temperature. -The temperature of a gas sample is independent of the average kinetic energy. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increases with increasing temperature

-The average speed of gas molecules decreases with decreasing temperature. -All the gas molecules in a sample cannot have the same kinetic energy. -There are gas molecules that move faster than the average. -The average kinetic energy of gas molecules increase with increasing temperature.

What is the difference between hybrid orbitals and molecular orbitals?

-hybrid orbitals are mixtures (linear combinations) of atomic orbitals from a single atom hybrid orbitals remain on central atom -molecular orbitals are combinations of atomic orbitals from 2 or more atoms. associated with entire molecule, not a single atom

molecular orbitals have what differences to atomic orbitals?

-molecular orbitals represent entire molecule, not a single atom -whenever 2 atomic orbitals overlap, 2 molecular orbitals are formed --> 1 bonding, 1 anti bonding

Trigonal bipyramidal can have 2 distinct positions in their geometry. What are they?

1. axial 2. equatorial (lone pairs occupy equatorial positions)

molecular orbitals have what similarities to atomic orbitals?

1. maximum of 2 electrons per orbital 2. electrons in same orbital have OPPOSITE spin 3. definite energy of orbital 4. can visualize electron density by a contour diagram

1. a single bond has how many sigma and pi bonds? 2. a double bond has how many sigma and pi bonds? 3. a triple bond has how many sigma and pi bonds?

1. single = 0 pi, 1 sigma 2. double = 1 pi, 1 sigma 3. triple = 2 pi, 1 sigma

what is the bond angle of H2O?

104.5 (NOT 90) tetrahedral, bent sp3 hybridization

mixing of the s and p orbitals yields what?

2 degenerate orbitals that are hybrids of the 2 orbitals and align themselves 180deg. from each other *sp orbitals have 2 lobes that look like a p orbital *1 of the lobes is larger and more rounded, as is the s orbital

Who's law is this? volume of gas at constant temperature and pressure is directly proportional to the # of moles of the gas

Avogadro's Law V1/n1 = V2/n2

Who's law is this? volume of fixed amount of gas at constant pressure is directly proportional to its ABSOLUTE temperature

Charles's law V1/T1 = V2/T2

If you combine 2 atomic orbitals on 2 different atoms to make a new orbital, is this a hybrid orbital or a molecular orbital?

MO b/c the AOs come from 2 DIFFERENT atoms

Which statements about a sample of gas containing molecules of different masses are true?

More massive gas molecules in the sample have lower rms speed than less massive ones. The average kinetic energy depends only on the temperature. However, a heavier molecule will move more slowly than a lighter molecule if both have the same kinetic energy.

Refrigerators are usually kept at about 5∘C, while room temperature is about 20∘C. If you were to take an "empty" sealed 2-liter soda bottle at room temperature and place it in the fridge, would you expect it to contract to one-fourth its original volume? 1. Yes, because 5 is one-fourth of 20. 2. No, because there is no gas inside the bottle. 3. No, because Celsius is not an absolute temperature scale.

No, because Celsius is not an absolute temperature scale. Note that 20∘C=293K and 5∘C=278K . So the absolute temperature has not decreased by very much at all, certainly not by a factor of 4. Therefore, the change in size of the plastic bottle would not be very noticeable.

According to Charles's law, for a fixed quantity of gas at constant pressure, which of the given quantities is constant?

V/T = constant

Avogadro's Law states that at a given temperature and pressure, what quantity is constant?

V/n Since V and n are directly proportional, the quantity V/n will always have the same value at a given pressure and temperature.

what is a chemical bond is in terms of electron density between 2 atoms?

a concentration of electron density b/t nuclei of 2 atoms. this concentration takes place b/c orbitals on the 2 atoms overlap

_______ - destructive combinations of atomic orbitals

anti bonding orbitals *a nodal plane occurs where electron density equals 0

_______ - constructive combinations of atomic orbitals

bonding orbitals

the sharing of space b/t 2 electrons of opposite spin in the valence-bond theory results in what kind of bond?

covalent bond *also know that --> the overlap of orbitals is when electrons of 2 atoms begin to occupy the same space

sigma and pi bonds are ______ bonds.

covalent bonds

double and triple bond electron domains vs. single bond electron domains

double and triple bonds have LARGER electron domains and exert a greater repulsive force --> making bond angles greater

How many electrons can be placed into each MO of a molecule?

each MO, like each AO or hybrid, can hold a maximum of 2 electrons

what is a hypervalent molecule?

elements that have MORE than an octet

_______ form by mixing of atomic orbitals to create new orbitals of EQUAL energy called _____ ______

hybrid orbitals degenerate orbitals

If you combine 2 atomic orbitals on 1 atom to make a new orbital, is this a hybrid orbital or a molecular orbital?

hybrid orbitals b/c the AOs are on the SAME atoms

how does a double or triple bond form?

it CANT if we only use hybridized orbitals. If you use orbitals that are NOT hybridized there is a "side-ways" overlap

Lewis structures vs Valence Shell Electron Pair Repulsion model (VSEPR)

lewis --> shows bonding and lone (nonbonding) pairs, but do NOT denote shape (they can help to determine shapes) VSEPR --> shows bonding and lone (nonbonding) pairs, but DO determine shape of molecule

_______ - bonding electrons (sigma or pi) that are specifically shared b/t 2 atoms

localized electrons vs. delocalized electrons - unable to describe all electrons as localized due to resonance

For the VSEPR model, "the best arrangement of a given # of electron domains is the one that ________ the repulsions among them."

minimizes

nonbonding/lone pair size vs. bonding pair size

nonbonding pairs --> physically LARGER causing their repulsions to be greater and compress bond angles

- side to side overlap -electron density above and below internuclear axis Is this describing a sigma or pi bond?

pi bond *multiple bonds have 1 sigma bond, all other bonds are pi bonds

-head to head overlap -cylindrical symmetry of electron density about internuclear axis - always single a single bond* -strongest form of covalent bonds Is this describing a sigma or pi bond?

sigma bond

what is an electron domain?

the direction to which electrons point In this example, the central atom(A) has 4 electron domains

What is meant by the term orbital overlap?

this occurs when a valence atomic orbital on 1 atom shares the same space with a valence atomic orbital on an adjacent atom

which electron domains can break the octet rule and have more than 4 bonds?

trigonal bipyramidal (5) octahedral (6)

All positions are equivalent in the octahedral domain. T/F?

true

For larger molecules, look at the geometry about each atom rather than the molecule as a whole. T/F?

true

Can antibonding molecular orbitals have electrons in them?

yes

Does the Pauli exclusion principle apply to MOs? Explain.

yes. the pauli exclusion principle states that no 2 electrons can have the same 4 quantum #s, meaning that the orbital can hold at most 2 electrons. this is true for atomic and molecular orbitals.