CEM 141 Chapter 3 Exam Questions| Already answered| GRADED A+
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Course
CEM 141
Institution
CEM 141
they have similar causes: electrostatic attraction of the electron of one atom to the nucleus of the other
- ANSWER-Similarities between LDF and Covalent Bond
1. magnitude of attraction
2. how the electrons are arranged in the new species formed by the interaction - ANSWER-Differences
between L...
CEM 141 Chapter 3 Exam Questions|
Already answered| GRADED A+
they have similar causes: electrostatic attraction of the electron of one atom to the nucleus of the other
- ANSWER-Similarities between LDF and Covalent Bond
1. magnitude of attraction
2. how the electrons are arranged in the new species formed by the interaction - ANSWER-Differences
between LDF and Covalent Bond
because valence electrons are attracted to the nuclei of other atoms - ANSWER-Why do bonds form
between atoms?
1. valence electrons from one atom become attracted to the nucleus of the other atom
2. each nucleus is attracting both electrons
3. when bonds form energy is released to surrounding - ANSWER-Covalent Bonds
the most stable distance between atoms (lowest PE) - ANSWER-What is bond length?
1. atomic orbitals can combine constructively to form a molecular orbital of lower energy (in phase)
2. atomic orbitals can combine destructively to form a molecular orbital of higher energy (out of phase)
3. combine n atomic orbitals--> n molecular orbitals
4. Bonding and Anti-bonding orbitals
a. both are in the same place of space, just at different energies - ANSWER-Molecular Orbital Theory
1. of lower energy than the atomic orbitals (typically)--> stabilizing
a. electrons in bonding orbitals make the species more stable - ANSWER-Bonding Orbitals
1. of higher energy than the atomic orbitals and destabilizing
a. electrons in anti-bonding orbitals make the species less stable - ANSWER-Anti-bonding Orbitals
,1. In H2: 2 electrons in a bonding orbital make 1 bond (H2 has one bond between 2 H atoms)
2. In He: 2 electrons in a bonding MO is stabilizing, but 2 electrons in an anti-bonding MO cancel out
stabilization (so no bonds between He atoms) - ANSWER-Why do 2 H atoms form a bond while 2 He
atoms don't?
1. In hydrogen-hydrogen, only the bonding MO is occupied, leading to a net stabilization of the
interaction
a. to break the bond, enough energy has to be added to raise an electron to the anti-bonding orbital
2. In helium-helium, both bonding and anti-bonding molecular orbitals are occupied. Because their
energies (negative for bonding orbital and positive for anti-bonding orbital) are equal and opposite,
there is no net stabilization for interaction - ANSWER-Bonding in H and He
20 - ANSWER-If we combine 2 atoms with 10 atomic orbitals each, how many molecular orbitals will
result?
1. O: 1s2 2s2 2p6
a. there are 5 atomic orbitals from each O being combined, 5+5= 10
i. Answer: 10 - ANSWER-If 2 elements in the second row (ex. 2 O atoms) were to interact, how many
molecular orbitals would be generated by the atomic orbitals in the core and valence shells?
2 bonds (only concerned with valence electrons) - ANSWER-How many bonds form between 2 O atoms?
1. shiny
2. conduct electricity and heat
a. because electrons can move freely
3. malleable and ductile
a. malleable because atoms can move with respect to one another
4. may be colored (gold, copper)- silver is colorless (like most metals) - ANSWER-What properties do
metals have?
1. lots of atomic orbitals combine with each other to form molecular orbitals (an equal number)
, 2. As the number of Molecular Orbital's increases, the energy distance between them decreases and
they form bands of Molecular Orbitals (of almost continuous energy)
3. electrons can move freely between Molecular Orbitals and over whole system - ANSWER-How does
bonding in metals explain their properties?
1. Absorption of a photon will promote an electron to a higher energy level
2. It immediately falls back down-emitting a photon-the metal shines
3. the metal interacts with light of many wavelengths, so the metal appears white or colorless (silvery)
a. metals are shiny because photons of many wavelengths are absorbed and then emitted - ANSWER-
Why are metals shiny? (properties of metals)
1. In Metallic bonding, the electron is promoted to a higher energy level, then comes back down to a
lower energy level (why it shines)
a. In Photoelectric Effect, the electron is completely leaving the atom - ANSWER-How is metallic
bonding, which causes the metal to shine, different from the photoelectric effect?
In metals, the valence band (bonding MO's) overlaps with the conduction band (antibonding MO's) -
ANSWER-Band Theory of Metals
1. In semi-conductors, there is a small gap between the bands
a. these materials are often used for solar cells and in computer equipment - ANSWER-Band Theory of
Semiconductors
Materials that are insulators (diamonds for ex.) have a large energy gap between the valence and
conduction band - ANSWER-Band Theory in Insulators
1. the interactions at the atomic/ molecular level
a. if we know the properties of a substance, we can use them to predict the type of bonding that is
present in that substance - ANSWER-What causes the properties of metals?
1. requires energy because you have to overcome attractive interactions (between molecules)
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