Chemistry 130
Practice Exam 1
February 19, 2002
Dr. Nash
100 Points Possible
NAME:__________________
Potentially useful constant: Avogadro's Number = 6.022 x 1023
1. What distinguishes an element from a compound or a mixture? What makes it special
2. Complete the following table (that includes completing the isotopic symbol (if
necessary):
Isotopic Symbol
52
number of protons
number of
neutrons
number of
electrons
Cr3+
242
Cf2+
77 3+
?
135
?
40
Sb3-
Pt2+
104
3. The atomic mass unit (amu) is the standard for measuring masses on the atomic scale.
(a) What is the definition of an atomic mass unit?
(b) What is the approximate mass (in atomic units) of
1 alpha particle (a helium nucleus)?__________
1 7Li isotope ? __________
1 electron? __________
(c) What fraction of a gram is one amu?
4. Copper, gold, and silver (Cu, Ag, and Au) are collectively known as the coinage
metals- because coins are frequently made using them.
(a) What will be the atomic number of the next coinage if it exists? Explain you
answer.
(b) Gold has two naturally occuring isotopes, one in 75% abundance an one in
25% abundance.
The atomic weight of Gold is 196.97 g/mol and the mass of the isotope in least
abundance is
199.212 amu. What is the mass of the heavier naturally occuring isotope?
(c) How many gold atoms are there in 1.0 grams?
(d) How many atoms of gold are there 3.27 x 10-22 g?
bonus:
(e) The atomic weight of Platinum is 195.08 amu and its two stable isotopes have
masses of
192.78 and 198.25. What are their relative abundances?
5. We learned that the Heisenberg Uncertainty Principle means that it is impossible for
someone to simultaneously determine both the position and motion of a subatomic
particle. (actually the statement of the Heisenberg Uncertainly Principle is somewhat
more complicated than this but our definition suffices).
Given this, we can see that it's really not correct to think of electrons 'orbiting' the nucleus
of an atom like a planet orbits the sun- we simply cannot use coordinates in the same way
for electrons as we do for planets. Instead, scientists have derived what are known as
quantum numbers which are used to describe the position and motion of electrons in a
different way. For atoms, we usually use 4 different types of quantum numbers Describe
them and what they stand for.
n
l
ml
ms
6. Using the proper rules for quantum numbers in atoms answer the following
(a) what is the maximum number of electrons allowed in the n=4 shell?
____________ ?
(b) how many subshells are allowed in the n=4 shell
____________ ?
list them______________________
(c) how many orbitals are there in the 4f subshell?
______________ ?
(d) how many electrons are allowed in an individual f orbital
_______________?
(e) how many electrons are allowed in the 4f subshell
_______________?
(f) how many orbitals are there in a 4p subshell
_______________?
(g) how many electrons are allowed in an individual p orbital?
_______________?
(h) how many electrons are allowed in the 4p subshell
_______________?
(i) how many orbitals are there in a 4d subshell?
________________?
(j) how many electrons are allowed in an individual d orbital?
_________________?
(k) how many electrons are allowed in the 4d subshell?
_________________?
(l) how many electrons are allowed in the 4s subshell?
7. Which of the following subshell labels are not allowed:
(a) 5g
(b) 2p
(c) 2f
(d) 7d
(e) 5f
(f) 2d
8. Discuss the trend in atomic radius as one travels from left to right across a row of the
periodic table.
9. For each of the following atoms or ions, circle the one that has higher ionization
energy.
(a) Rb+ or Kr
(b) Br- or Kr
(c) Sr2+ or Rb+
(d) Sr or Rb+
(e) Br- or Cr2+
Kr, Rb+, Br-, and Sr2+ have something in common, what is it?
10. Predict the formulas of the ionic compounds formed by the following pairs of
elements.
(a) K and S
(b) Li and N
(c) Al and Br
(d) Te and H
(e) P and Mg
(f) At and Cs
11. Remember I gold a coinage metal in a previous question It is known that despite its
position on the periodic table, gold has an electron configuration of 6s15d10 and when
forming compounds gold usually loses only its valence s electron. Copper and Silver
exhibit the same ‘odd’ behavior.
(a) Given this, predict the formula for the tarnished silver, that is the oxide of
silver metal.
(b) It is a fact that half-filled and fully filled subshells in atoms are conferred with
a ‘special
stability.’ That is, it is usually favorable for atoms to adopt these electron
configurations and resist changes in them when forming bonds. How does this
explain the odd electronic configurations of copper, silver, and gold?
12. Write the electron configurations for the following atoms or ions:
(a)
(b)
(c)
(d)
(e)
(f)
B
At+
As3+
Ba
Bi+
Ho3+
13. Formaldehyde, H2CO, is a common substance frequently used to preserve the severed
heads of unruly
chemistrh students.
(a) Draw the Lewis Structures for this molecule.
(b) How many unshared pairs of electrons are on the oxygen?
14. Ozone, O3, is a major component of the upper atmosphere and an invaluable source
of protection from solar UVA radiation. (and it really is being destroyed by man made
compounds-the protestations of Rush Limbaugh notwithstanding)
(a) Draw a correct Lewis structure for this molecule.
(b) How many unshared electron pairs on the central oxygen atom does ozone
have?
(c) How many resonance structures does ozone have? Draw them.
15. In comparing two ionic compounds RbF and SrO, we notice that the Rb-F distance is
about the same as the SrO distance. Which bond is stronger and by how much?