Inorganic Chemistry 422
Exam 1
Feb. 8, 2005

All work must be shown for any credit to be given.

(6 pts.)    1. Describe the trends in atomic radius across a period and down a group. Your description should include as a minimum what the trend is and what causes it.

The atomic radius decreases left to right across a period. As electrons are added to the electron cloud of each additional element, protons are added to the nucleus. These protons act as a point charge witht the elctrons acting as individual charged species. This causes the nucleus to pull all of the electrons closer to the nucleus.

The atomic radius increase top to bottom down a group of the periodic table. This is the result of the outer electrons being somewhat shielded from the nuclear charge by the inner electrons allowing the electron cloud to expand to a larger radius.

(6 pts.)    2. Coordination number 4 has two different shapes.  What are their shapes and what is the hybridization of each shape?

square planar: dsp² or sp²d

and

tetrahedral: sp³

(4 pts.) 3. Compare allotropes to isotopes of elements.  Give an example of an element (other than carbon) that exhibits both.

Allotropes are examples of the sample element with different molecular forms. Isotropes are atoms of the same element with different numbers of neutrons.

oxygen: O₂ and O₃ allotropes; O-16, O-17, and O-18 isotopes

(6 pts.)    4. Complete the nuclear reaction by supplying the missing information:

               (a.)    ₉₂U²³⁸  +  ₀n¹  à ₉₂U²³⁹ +  ₀g⁰

               (b.)  ₉₂U²³⁵  +  ₀n¹  à  ₃₄Se⁸⁵  + ₅₈Ce¹⁴⁸ + 3 ₀n¹

(2 pts.)    5. What is the value of the “l” quantum number for a “g” electron?

l = 4 for a "g" electron

(4 pts.) 6. Draw the bonding and antibonding orbital resulting from the end-to-end overlap of a p_z and another p_z atomic orbital.

(6 pts.)    7. Give the ground-state electron configuration of:

(a.)    Cr atom 1s²,2s²,2p⁶,3s²,3p⁶,4s²,3d⁴ or [Ar]4s²,3d⁴

(b.)    Cr⁺³ ion 1s²,2s²,2p⁶,3s²,3p⁶,4s⁰,3d³ or [Ar]4s⁰,3d³

(4 pts.)    8.  Iron, cobalt, and nickel are grouped together because of their magnetic characteristics.  What type of magnetism do they possess?  Explain this type of magnetism.

They possess ferromagnetism where the electron spins within a domain are aligned and all of the domains are likewise aligned.

(2 pts.)    9. Consider the structure of cesium chloride.

What is the coordination number of the anion and cation?
8 and 8

(3 pts.) 10. Why is cesium chloride not body-centered cubic?

Body centered cubic unt cells have the same element in the corners of the unit cell as well as the center of the body. Cesium chloride has different elements at the corners of the unit cell than the one in the center of the body.

(3 pts.)    11. Why is sodium chloride face-centered cubic?

With sodium chloride, both sodium ions and chloride ions form the face-centered cubic lattice of have ions at the corners of the unit cell and at the center of each face.

(4 pts.)    12. Write the Lewis electron dot structure for the CO₃^-2 ion.

one of three resonance structures

(6 pts.)    13. What angle or angles are found for the following hybridizations:

(a.)   sp             180^o

(b.)   sp²            120^o

(c.)   sp³            109.5^o

(d.)  dsp²           90^o

(e.)  dsp³           90^o and 120^o

(f.)     d²sp³         90^o

(8 pts.)    14. The colorless gas N₂O₄ is a dimer of the reddish-brown gas NO₂.  Draw two of the possible resonance Lewis electron dot structures of N₂O₄.

or

(6 pts.)   15. Draw the molecular orbital energy level diagram for paramagnetic O₂ and give its bond order.

for O₂

bond order = (bonding electrons - antibonding electrons)/2 = (6-2)/2 = 2

There are two unpaired electrons, making it paramagnetic.

Name ___________________________

Inorganic Chemistry
Take Home Exam 1
Due by 4 P.M. Feb. 10, 2005

All work must be shown for any credit to be given.

(4 pts.)    16. Using the Slater Rules, calculate the effective nuclear charge for the 4p electrons in Ge.

[1s²][2s²2p⁶][3s²3p⁶][3d¹⁰][4s²4p²]
n - 2 group => 10 * 1.0
n - 1 group => 18 * 0.85
n group => 3 * 0.35

Z* = 32 - ((10 * 1.0) + (18 * 0.85) + (3 * 0.35)) = 32 - 10 - 15.3 - 1.05 = 5.65

(16 pts.)  17. Using the VSEPR theory, predict the shape of the following using the Lewis electron dot structure, the number of bonding pairs, and number of lone pairs of electrons.

(a.)            PF₆^-1 ion


6 bond pairs; 0 lone pairs; thus octahedral shape

(b.)           IF₃  molecule


3 bond pairs; 2 lone pairs; thus T-shape

(2 pts.)    18. Draw a “delta” bond (the fourth bond in a quadruple bond) showing the atomic orbitals that are combined in its formation.

(4 pts.)    19. Explain the pattern of the First Ionization Energies of the elements Atomic Number 1-18 shown in the chart below.

As the atom gets smaller, the ionization energy increases, and, by the same token, as the size increases the ionization energy decreases. The ionization energy reaches its maximum with a completed energy level or shell. In this chart, the First Ionization Energy increases from H to He where the shell is completed. The next shell is further from the nucleus, thus the First Ionization Energy (FIE) falls from He to Li. The FIE increases to Be as the 2s subshell is filled and the size decreases. This is followed by a small decrease as the 2p subshell begins to fill. The FIE now increases steadily from B to C to N as the 2p subshell becomes half filled. There is then a small decrease in FIE as the first 2p orbital has a pair of electrons in O. The steady increase returns for the O to F to Ne filling of a second electron in the other 2p orbitals. As expected the start of the 3rd shell results in a decrease in FIE for Na followed by an increase to Be as the 3s in filled, followed by a slight increase as the 3p begins filling for Al, followed by steady increase Al to Si to P, followed by slight decrease in S as the pairing of 3p electrons begins, and then followed by a staedy increase S to Cl to Ar as the 3p electrons are paired in the completion of the 3rd shell.

(4 pts.)    20. What is the ratio of the radius of the cation to the radius of the anion for the face-centered cubic arrangement of anions about the cations in the NaCl structure.  Assume that there is anion-anion contact along the body face diagonal of the unit cell.

As shown above, the gray anions on the corners and center of the face are in contact. The diagonal across this face is equal to 4 radii of the anion. The blue cations touch the gray anions along the edge. The edge dimenion is 2 radii of anion plus 2 radii of cations.

face-diagonal = 4r_a

edge = 2r_a + 2r_c

(4r_a)² = (2r_a + 2r_c)² + (2r_a + 2r_c)²

(4r_a)² = 2(2r_a + 2r_c)²

4r_a = 2^1/2(2r_a + 2r_c)

2r_a = 1.41r_a + 1.41r_c

0.59 r_a = 1.41r_c

0.414 = r_c/r_a

I neither received nor gave assistance on this take home exam, nor did I see others giving or receiving assistance.

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