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CHE 124A > Week 2 > Flashcards

Week 2 Flashcards

(65 cards)

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1
Q

What does n determine?

A

1) The energy levels of an electron (electron shell)

2) The size of the electron’s orbital (radial wave function depends on n)

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2
Q

What about n in the H atom?

A

All orbitals with the same value of n are in the same principal electronic shell and are degenerate (have the same energy)

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3
Q

What is RPD? and what does it show?

A

Radial Probability Distribution Function - it shows the probability of finding an electron in a shell of thickness of dr at a distance of r from the nucleus

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4
Q

What is the equation for solving for probability?

A

Probability = volume x probability density

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5
Q

What does L determine?

A

1) The SHAPE of the orbital
2) The subshell
3) The electron’s orbital angular momentum

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6
Q

Which orbital is a n=4 and l=3?

A

It is a 4f orbital

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7
Q

What is a node?

A

A point or plane at which the wavelength equals 0.

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8
Q

How to calculate nodes?

A

n-1

n being the principal quantum number

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9
Q

How to calculate planar (angular) nodes?

A

= L

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10
Q

How to calculate radial nodes?

A

n-1-L

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11
Q

What does a multielectron atom have that a single electron atom does not?

A

Shielding

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12
Q

What does a 2s electron do better than a 2p electron?

A

Shield the nucleus due to its closer proximity

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13
Q

Shielding ability s,p,d

A

3s>3p>3d

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14
Q

How does the 4s electron penetrate inner shell electrons in comparison to the 3d?

A

More efficiently in neutral atoms

This REVERSES in positive ions

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15
Q

order of orbital filling neutral atoms

A

4s-3d-4p

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16
Q

order or orbital filling for positive ions

A

3d-4s-4p

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17
Q

What is the EC for V3+ if V = [Ar] 4s23d3

A

[Ar]3d2, D orbitals will fill first since we have a positive ion

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18
Q

What are the 5 periodic table trends?

A

Ionization energy, electron affinity, atomic radius, electronegativity, and metallic character

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19
Q

What are the THREE driving forces?

A

1) Effective nuclear charge
2) Shielding
3) Electron-electron repulsion

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20
Q

What is Slater’s eqn?

A

Zeff = Z-S
Z being nuclear charge and S being the shielding constant
Z also equals the atomic number

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21
Q

What do ns, np, (n-1), (n-2) electrons have an S value of for ns and np orbitals?

A

ns,np; S = 0.35
(n-1)d S=0.85
(n-2)f S=1

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22
Q

What do ns, np, (n-1), (n-2) electrons have an S value of for nf and nd orbitals?

A

nd,nf electrons are S= 0.35

All lower level electrons contribute S=1

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23
Q

What are the three ways atomic radius is defined?

A

metallic radius, covalent radius, and Van der waals radius

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24
Q

Define metallic radius

A

Half the distance between the nearest neighbor atoms in a solid state metallic lattice

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25
Define covalent radius
Half the covalent bond length of a homo-nuclear X-X single bond
26
Define Van der waals radius
Half the distance of closest approach to two non bonded atoms of X
27
Define Ionization energy
Energy (or enthalpy) associated with the removal of the first valence electron in the gas phase
28
Is the addition of an electron to an atom usually endo or exo thermic?
The addition of an electron to an atom is usually an exothermic process
29
What are the two forces driving electron affinity?
1) Attraction between nucleus and incoming electrons | 2) Repulsion between extra electrons and valence electrons
30
What are the three different scales of electronegativity?
Pauling, Mulliken, & Alfred-Rochow
31
What is a Coloumbic explosion?
a mechanism for transforming energy in intense electromagnetic fields into atomic motion and are thus useful for controlled destruction of relatively robust molecules. The explosions are a prominent technique in laser-based machining, and appear naturally in certain high-energy reactions
32
What is Hess's Law?
The thermodynamics of metallic ions depends critically on their sizes and formal charges More energy is released when water molecules encapsulate a small highly charged ion due to larger electrostatic forces
33
What are the two main theories in bonding?
Valence bond Theory and molecular orbital theory
34
What is the key to bonding in Lewis structures or according to Lewis?
Atom achieves noble gas configuration, electrons are represented by dots, bonds are represented by a -
35
What are the basic concepts for Lewis
1) Draw a skeletal structure 2) Count valence electrons (factor in negative or positive for ions) 3) Obey octet rule 4) Make sure formal charge on each atom checks out
36
How to calculate formal charges?
FC = V-L-S V= Valence L= Number of loner electrons S- Number of bonds
37
3 rules of where to place the formal charge
1) The sum of atoms FC must equal 0 in a neutral molecule 2) Negative formal charge should be on the most electronegative atom 3 Positive formal charge should be on the most electropositive atom
38
What are the three exceptions to the octet rule?
1) Be & B often have fewer than 8 electrons 2) 2nd row elements always obey the octet rule 3) 3rd & 4th row elements can have more than 8 electrons
39
What does delocalization do?
Spreads electron density and makes the molecule more stable
40
The SEVEN aspects of valence bond theory
1) Separate atoms are brought together to form molecules. 2) The electrons in the molecule pair to accumulate density in the internuclear region. 3) The accumulated electron density “holds”the molecule together. 4) Electrons are localized(belong to specific bonds). 5) Basis of Lewis structures, resonance, and hybridization. 6) Very poor theory for obtaining quantitative bond dissociation energies. 7) Good theory for predicting molecular structure.
41
What is VSEPR theory used for?
To predict the shapes of molecules and ions | *based on the assumption that electron pairs adopt arrangement that minimize repulsion between them
42
What does the coordination number (CN) include?
The number of bonds and lone pairs that will correlate to the geometric nature of the molecule
43
2-coordination molecules can be? (2)
Linear & Bent
44
3-coordination molecules can be? (3)
Trigonal planar, T-shapes, Trigonal pyramidal
45
4-coordinate molecules can be? (3)
Square planar, tetrahedral, disphenoidal
46
5-coordinate molecules can be? (3)
trigonal bi-pyramidal, square based pyramidal, pentagonal planar
47
6-coordinate molecules can be? (1)
Octahedral
48
7-coordinate molecules can be (1)
Pentagonal by-pyramidal
49
8-coordinate molecules can be? (1)
Square antiprismatic
50
What minimizes repulsions between lone pairs?
Placing them on equatorial positions rather than axial positions
51
What does the dipole moment of a polyatomic molecule depend on?
``` Bond polarity (covalent polar bond) Molecular geometry ```
52
What are the FIVE aspects of molecular orbital theory?
1) Molecular orbitals are formed by the overlap and interaction of atomic orbitals. 2) Electrons then fill the molecular orbitals according to the aufbau principle. 3) Electrons are delocalized(don’t belong to particular bonds, but are spread throughout the molecule). 4) Can give accurate bond dissociation energies if the model combines enough atomic orbitals to form molecular orbitals. 5) Model is complex and requires powerful computers for even simple molecules.
53
What do MOs describe?
The circulation of electrons in a molecule
54
What are MOs formed from?
The atomic orbitals of atoms in the molecule (only AOs with similar energies contribute to a given MO
55
What are the two types of covalent bonds?
1) Results from head on overlap of orbitals | 2) Electron density is symmetric about the internuclear axis between nuclei
56
Bonding molecular orbital
–cylindrically symmetrical along the bond axis –No nodal plane between the nuclei g–(from German “gerade” –even) –parity label
57
Anti-bonding molecular orbital
-cylindrically symmetric along the bond axis * -Nodal plane between the nuclei (⊥bond axis) u–(from german“ungerade” –odd) –parity label
58
Does MO change upon rotation around internuclearbond axis (line connecting two nuclei)?
Yes for pi, no for sigma
59
Does MO have nodal plane between two nuclei?
yes, anti-bonding superscript * | no for bonding MO
60
Does MO change upon inversion through the center of molecule?
Yes - subscript U | No - subscript G
61
What is the bond order?
The bond order is a measure of net bonding and is useful in determining relative bond strengths in molecules. 1/2(#bonding electrons - # nonbonding electrons)
62
What is paramagnetic?
Strongly attracted by a magnetic field, O2 is paramagnetic (remember the liquid nitrogen display)
63
What is diamagnetic?
Weakly repelled by a magnetic field
64
What can we say about electrons in molecules that are paramagnetic?
They must have unpaired electrons that enable the magnetic attraction
65
O2
The two unpaired anti-bonding electrons in O2 are what make it paramagnetic

CHE 124A (2 decks)

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