CHM Final Exam

Question 1

T or F - For an electron that is excited from the ground state to the n=3 state in a hydrogen atom, the first excited state corresponds to n=3

Answer 1

False. n=2 is the first excited state, and n=3 is the second excited state.

Question 2

T or F - for an electro that is excited from the ground state to the n=3 state in a hydrogen atom, the wavelength of light emitted if the electron drops from n=3 to n=2 is shorter than the wavelength of light emitted if the electron falls from n=3 to n=1

Answer 2

False. Wavelength and energy are inverse of the other. Less energy from n=3 to n=2 means a longer wavelength

Question 3

T or F - the 1s orbital has a higher probability of being close to the nucleus than the 2s orbital or 2p orbital

Answer 3

True. 1s peaks closer to the nucleus than the others (GRAPH)

Question 4

T or F - the shell number (n) determines approximately how far an electron is from the nucleus on average. Thus, all orbitals in the same shell (s,p,d,f) are, on average, about the same distance from the nucleus.

Answer 4

True. ON AVERAGE the 2s and 3p orbitals have the same distance from the nucleus. The 2s orbital can get closer to the nucleus than the 2p, but on average they are similar distances.

Question 5

T or F - shielding is the reduction of true nuclear charge (Z) to the effective nuclear charge (Zeff) by other electrons in a multi-electron atom or ion

Answer 5

True. Shielding reduces the attractive “pull” that the outer e- feels from the nucleus, b/c e- is closer than the nucleus to “shield” them. Shielding occurs in all elements but H.

Question 6

T or F. Core electrons shield valence electrons, but valence electrons have little effect on the Zeff of core electrons.

Answer 6

True

Question 7

T or F. The ability to shield, and be shielded by, other electrons strongly depends on the electron orbital’s average distance from the nucleus and its penetration; thus shielding depends on both shell (n) and subshell (l)

Answer 7

True

Question 8

T or F. Electrons in the 3s and 3p orbital have identical energies in poly electronic atoms.

Answer 8

False. electrons in different sub shells in the same shell have different energies in multi-electron atoms. 3s has energy in poly electronic atoms.

Question 9

Why is the energy order 3s < 3p < 3d?

Answer 9

Because when multiple electrons present, penetration and shielding make some electrons lower in energy

Question 10

T or F. 3s, 3p, and 3d orbital have the same energy in the hydrogen (H) atom.

Answer 10

True - subshells in the same shell have the same energy in the H atom. In the H atom, the energy of an orbital depends only on its quantum number.

Question 11

T or F. Electrons in the 1s, 2s, and 2p orbitals “shield” the electrons in the 3s orbitals from nuclear charge, so electrons in the 3s orbitals do not spend time near the nucleus

Answer 11

False. The 3s orbital has a small but significant probability of being close to the nucleus cloud. We say it penetrates the shield core electrons and feels more of the nuclear charge.

Question 12

3s 3p 3d. As you to the right, the penetration effect:

Answer 12

Decreases. The electrons in the 3s orbital are more able to penetrate the core electrons to feel nuclear attraction.

Question 13

T or F. Electrons fill the 4s orbital before the 3d orbital.

Answer 13

True

Question 14

T or F. Electrons in the 4s orbital are more likely to spend their time closer to the nucleus than electrons in the 3d orbital due the penetration effect.

Answer 14

False. electrons in the 4s orbitals have a strong penetration effect, so they can get closer to the nucleus, but the majority of their time is spent further away

Question 15

Which is further away from the nucleus on average: 2p or 3s?

Answer 15

3s

Question 16

Which is more penetration: 2p or 3s?

Answer 16

3s

Question 17

Which orbital is lower in energy: 2p or 3s?

Answer 17

2p

Question 18

Which atom, Li or N, has a stronger valence Zeff?

Answer 18

N has a stronger Zeff because it has more protons. Greater atomic number, greater Zeff.

Question 19

T or F. 2s and 2p subshells are completely degenerate (have the same energy) in a hydrogen atom.

Answer 19

False. They are different energies in poly electric atoms, but the same in hydrogen atoms.

Question 20

Which electrons shield others more effectively: 3p or 3d?

Answer 20

3p; p orbitals penetrate more than d orbitals within the same shell

Question 21

Which atom has a smaller radius: Be or F?

Answer 21

F: it has a greater Zeff, meaning it pulls its valence electrons closer to the nucleus.

Question 22

Si, Si+, Si2+, Si3+. As you go right, the ionization energy:

Answer 22

increases

Question 23

T or F. The ionization energy remains constant for each electron removed from an ion.

Answer 23

False. Ionization can change depending on which sub shell you try to remove the electron from

Question 24

T or F. Ionization energies depend upon atomic radius.

Answer 24

True. Atomic radius increases and ionization radius increases.

Question 25

T or F. As the nuclear charge decreases, the ionization energy increases.

Answer 25

False. As nuclear charge increases, there is a greater pull on the electrons by the nucleus and the ionization energy increases

Question 26

T or F. As the distance of an electron from the nucleus increases, the ionization energy decreases.

Answer 26

Outer electrons are easier to remove because they’re shielded by the core electrons and experience less nuclear charge. Even 3p electrons are shielded by 3s electrons in addition to the core electrons (2p electrons)

Question 27

Na has a higher positive charge than Li. However, the ionization energies of removing the outermost electron from Na and Li are 495 and 520 kJ/mol respectively. Why does the outermost electron in Li have the higher ionization energy?

Answer 27

The reasons are increased distance and increased shielding of the outermost electron in Na.

Outermost electron in Na sits in the 3s orbital, while outermost electron in Li sits in the 2s orbital. The electron in the 3s orbital is farther away, making it easier to remove. Also, as the 3s electron is further away, it is also shielding form nuclear charge by core electrons. Both increased distance and increased shielding make a lower ionization energy.

Question 28

Typically, the ionization energy increases as you go to the right in a period, due to increasing nuclear charge. However, for example, the first ionization energy is 735 kJ/mol for Mg and drops to 480 kJ/mol for Al (to the right of Mg in the period). Explain why this is observed.

Answer 28

First ionization energy for Mg corresponds to the removal of the 3s2 electrons, while that for Al corresponds to the removal of 3p1 electrons.

Question 29

T or F. Paired electrons are easier to ionize (remove) than unpaired electrons.

Answer 29

True. Due to electron-electron repulsion.

Question 30

As more energy is released, the electron affinity becomes more positive.

Answer 30

False. The electron affinity becomes more negative as more energy is released.

Question 31

Which group in the periodic table releases most energy when an electron is added?

Answer 31

Halogens, group 7A. They really want another electron to fill the octet shell and become stable like the noble gases.

Question 32

Which atom has the larger ionization energy: As or S?

Answer 32

S. Ionization energy increases as you go up and to the right

Question 33

Elements with very large ionization energies also tend to have highly exothermic electron affinities. Which group of elements would you expect to be an exception to this statement?

Answer 33

Noble gases are the exception. The noble gases have a large IE but an endothermic EA. Because they have a stable arrangement of electrons, adding an electron disrupts this stable arrangement, resulting in unfavorable electron affinities.

Question 34

Ionic compounds have low electrical conductivity as solids and high conductivity in solution or when molten. Why?

Answer 34

For electrical conductivity, charged species must be free to move. In ionic compounds, the charged ions are held rigidly in place. Once the forces are disrupted (melted or dissolution), the ions can move about.

Question 35

T or F. Ionic compounds have relatively high melting points and boiling points.

Answer 35

True. Melting and boiling points disrupts the attractions of the ions for each other. Because these are electrostatic forces (strong too), it will take a lot of energy to accomplish this.

Question 36

Ionic compounds tend to brittle. Explain why.

Answer 36

If we try to bend a piece of ionic material, the ions must slide across each other. Just as the layers begin to slide in an ionic compound, there will be very strong repulsions causing the solid to snap.

Question 37

Photoelectric Effect

Answer 37

Emission of electrons from matter as it is bombarded with protons

Question 38

Double slit experiment

Answer 38

relates to a wave particles duality

Question 39

Blackbody radiation

Answer 39

temperature dependent emission

Question 40

What does it mean when an atom is “quantized”?

Answer 40

It means that there are discrete energy levels within the atom. In particular, there are certain energy levels allowed for an electron. The atom has “steps” not a “ramp” of energy.

Question 41

In 5 valence pair electronic geometry, explain why lone pairs of electrons fill the “equator” of the structure before the “axial” positions

Answer 41

The equatorial have 2 90 degree bond angles, while the axial positions have 3. In order to minimize the repulsive interactions of the bulky lone pair, it will occupy the position with the fewest small bond angles, which happens to be the equator one.

Question 42

Difference between electronic and molecular geometry?

Answer 42

Electronic –> counts for lone pairs and repulsive groups around the bonds
Molecular –> does not care about lone pairs, and only cares about atomic positions so we ignore the lone pairs.