CHEMISTRY 150 C

 

HOUR EXAM

Winter 1997

 

Friday, January 24, 1997

 

 

 

Name: ____________________

TA Section: _______________

 

Student Number: ___________

TA Name: ________________

 

 

 

 

SHOW YOUR WORK IN THE SPACE PROVIDED
GOOD LUCK !!

Score: I ________

(of 45)

II ________

(of 40)
 

III ________

(of 15)

 

Extra ________

(of 10)

 

TOTAL ________

(of 110)

 

 

 

PART I (SHORT ANSWER, 3 points each)

 

1. Name the four quantum numbers which uniquely describe each electron in an atom or molecule, and give the range of possible values of each.

2. Rank the following atomic or ionic species in order of INCREASING atomic radius:

 

K

K+

Ne

Na

Ar

3. Rank the following atomic or ionic species in order of INCREASING ionization energy:

 

Na

Na+

Ne

O

Cs

4. What is the maximum number of electrons which can occupy the n=3 energy level of an atom?

5. Fill in the energy level diagram for the O+ ion with arrows ( ! ) indicating spin orientation of the electrons.

2s ____

2p ____ ____ ____

 

 

1s ____

 

6. How does ionization energy (IE) vary across a horizontal row of the periodic table and why?

7. For an oxygen atom O (1s2 2s22p4), write all possible excited electronic configurations for n < 3

8. Which of the following species is paramagnetic? What is the net spin S ?

 

Ca+2

Br - Zn Se

 

9..Consider removing an electron from each of the following iso-electronic species:

 

O-2

F -

Ne

Na+

Mg+2

Below each species, give the corresponding ionization process ( IE(1st), IE(2nd), EA(1st) , etc).

10. Which of the following molecules has non-polar covalent bonding?

 

IBr

PI3

I2

SF4

 

11. Write all possible structural isomers of pentane, C5H12 (Use lines to link carbon atoms, don't show the hydrogens)

12. The adjacent figure shows the amplitude of the wavefunction for an electron in an atom as a function of the distance (r) from the nucleus. On the same figure, draw a curve representing, the square of the wavefunction, which is the probability of finding the electron at that distance. What are the values of (n, l) for this electron?

13. Which of the following compounds contains both ionic and covalent bonds?

KCl

Na2O2

CH2I2

BF3

14. The central atom in each of the following species has a steric number of four EXCEPT (circle one):

 

SF4

H3O+

NH4+

CF3-

 

15. Give the ground state electronic configuration (1s2 2s2.... etc) for each of the following atoms or ions: (You may use the inert gas core short notation)

Fe

 

 

Br-

 

 

As+

 

 

 

 

 

PART II: Lewis Structures and Hybrid Bonding (points as indicated)

1.(30) Draw the Lewis structures for each of the following molecules or ions, including resonance structures if appropriate:

(a) BCl3

(b) NH3

 

(c) O3

(d) SF4

 

(e) NO3-

(f) ICl3

 

 

 

 

2. (10) Complete the following table for hybrid bonding:

Steric no.

Hybridization

Spatial Arrangement

Bond Angles

Example

2

sp

 

180

 

3

sp2

 

 

 

4

sp3

tetrahedral

109

CH4

5

sp3d

 

 

 

What is the general effect on the bond angle in these structures when a bonding atom is replaced by a lone pair of electrons?

 

 

PART III (quantitative, 15 pts) IONIZATION ENERGY

1. Calculate the energy required to ionize 13.7 g of sodium vapor (Na) to form Na+ The first ionization energy of Na is I.E. = 0.496 x10+3 kJ/mol,

NA = 6.022 x10+23

 

EXTRA CREDIT (10 points):

The energy levels of the iso-electronic series (H He+ Li+2 ) are described by a simple equation:

E = - R(Z/n)2

Complete the following chart of ionization energies and related properties:

Species

I.E.(n=1)

I.E.(n=2)

Z

Zeff

H

R

R/4

1

1

He+

 

 

 

 

Li+2

 

 

 

 

Why don't the energy levels of these species depend on the value of the azimuthal quantum number "l" (s,p,d,f...) ?