Homework Packet / Unit 2
HW #2.1: Contained in separate handout
HW #2.2
1. Explain the difference between:
a. heterogeneous and homogeneous mixtures
b. a pure substance and a mixture
c. a compound and an element
d. physical and chemical changes
2. (a) Classify each of the following as a pure substance or a mixture and
(b) For each pure substance, indicate whether it is an element or a
compound. Which of the mixtures are solutions vs. crude mixtures?
a. air
f. gasoline
k. silicon
b. uranium
g. salted popcorn
l. pure water
c. wood
h. sulfur
m. tap water
d. table salt (non-iodized)
i. sweetened tea
n. lead
e. sugar
j. carbon dioxide
o. oxygen gas
3. Classify the following changes as physical or chemical:
a. pumping oil out of a well
b. separation of components of oil by distillation
c. burning gasoline
d. grinding up beef in a meat grinder
e. digestion of beef
f. baking bread
g. mixing flour with yeast
h. fermentation to produce beer
i. smashing a car against a tree
j. burning your chemistry book
k. burning toast
4. What kind of experiment would you carry out to demonstrate that
seawater is a solution rather than a pure substance.
HW #2.3
1. For the following compounds, determine the number of molecules/formula
units and the number and type of atoms contained in the molecules/FU:
a. NaOH
d. 3 HNO3
g. 2 N2O5
j. 4 Ba(OH)2
b. NH3
e. 4 Ag
h. Mg2(PO4)3
c. K2SO4
f. 6 Cl2
i. 3 C12H22O11
Example:
1.a. 1 formula unit; 1 atom Na, 1 atom O, 1 atom H
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2. Illustrate how the atoms rearrange in the following reactions using
spheres for atoms (don't worry about the atoms being in the correct
arrangement; just make sure you have the correct number of each atom.
We will study correct arrangements of atoms in later units).
a.
b.
c.
d.
SO3
H2O  H2SO4
CaCO3
 CO2 +
+ 5 O2 
2 P2O5
+ KCl
 AgCl +
+
P4
AgNO3
CaO
KNO3
HW #2.4
1. Which part of Dalton's Atomic Theory was affected by the discovery of
subatomic particles?
2. What are cathode rays? Why are they called cathode rays? How do cathode
rays act differently than ordinary light?
3. What evidence from Rutherford's gold-foil experiment led him to propose
that the atom had a central region he called the nucleus?
4. Where are the protons, neutrons, and electrons located in Rutherford's atomic model?
5. Compare the mass and volume of the nucleus to that of the whole atom.
6. Explain what each of the following scientists contributed to atomic theory.
a. John Dalton b. J.J. Thomson
c. Ernest Rutherford
7. Complete the following table in your homework:
Nuclear
Symbol
a.
b.
c.
d.
No. of
Protons
No. of
Neutrons
No. of
Electrons
Atomic
Number
Mass
Number
12 C
6
Charge/
Valence
0
5
6
13
12
4
9
8. A particular atom of potassium contains 19 protons, 19 electrons, and 20
neutrons. What is the atomic number of this atom? What is the mass number
of this atom? Write the symbol for this nucleus.
9. Yttrium was discovered in 1794. It is one of the elements used in
superconductors. How many electrons, neutrons, and protons are in atoms
of yttrium with mass number 88?
10. Why is the mass of the atom (mass number) found by adding the protons
and neutrons and does not include the electrons?
HW #2.5
1. Which part of Dalton's Atomic Theory was affected by the discovery of isotopes?
2. What is the difference between 23892U and 23592U?
3. What is meant by "relative abundance?"
4. Compute the average atomic mass of silver, if 51.83% of the silver atoms
occurring in nature have a mass of 107 amu and 48.17 % of the atoms have a
mass of 109 amu.
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5. A certain element consists of two isotopes which have atomic masses of
10.0 and 11.0. Their abundances are 18.8% and 81.2% respectively. What is
the average atomic mass of the element? Which element is it?
6. Give the number of protons and electrons in the following ions:
a. Li+
b. Fc. Mg2+
d. S27. Complete the following table in your homework:
Nuclear
Symbol
No. of
Protons
No. of
Neutrons
No. of
Electrons
10
Atomic
Number
Mass
Number
Charge/
Valence
a. 168O2b. 2713Al3+
c.
8
8
12
12
+2
d.
17
19
-1
-2
8. Write the equation that shows the formation of these ions from their
neutral atoms:
a. Ca2+
b. K+
c. O2d. Brexample: Cl + e-  Cl9. Draw the formation of Mg2+ ion using simple atom diagrams.
anion
HW #2.6
1. How is an x-ray able to generate an image on film?
2. Compare the penetrating power of the three types of radiation emitted by
radioactive elements.
3. What is meant by "radioactive decay"?
4. Why is radioactivity potentially harmful to humans?
5. What was Marie Curie's contribution to atomic theory?
6. Fill in the missing parts of the following nuclear equations and identify the type
of radiation emitted:
a. 21082Pb  21083Bi + ____
b. 146C  ____ + 0-1e
c. 22688Ra  ____ + 42He + gamma ray
HW #2.7
1. Explain what each of the following scientists contributed to atomic theory.
a. Niels Bohr
b. Erwin Schrodinger
2. Give two uses of the phenomena whereby atoms give off colorful light when
supplied with energy.
3. Explain what led Bohr to believe that electrons could only be found at
certain energy states/levels?
4. What is meant by "ground state" and "excited state" in describing an electron?
5. Bohr's atomic theory was originally thought to be brilliant. What went wrong?
6. Schrodinger was able to solve the puzzle of the atom's structure by using
probability. What is probability?
7. What does an electron cloud tell us about the location of an electron?
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HW #2.8
1. A baseball game is being played in a circular stadium with a sell-out crowd.
Draw a probability diagram to show the probability of finding a spectator at a
given distance from the pitcher's mound (located at the center of the stadium).
Use heavy shading to indicate where there is a heavy density of spectators.
2. Redraw the probability diagram for the following:
a. there was a riot on the field in which many spectators took part.
b. the stadium was only half-full of spectators.
3. How many orbitals are there in the following subshells: s, p, d, and f?
4. How many electrons will fill each of the following subshells: s, p, d, and f?
5. Give the total capacity for electrons of the principal energy level (shell) for which:
a. n = 1
b. n = 2
c. n = 3
d. n = 4
6. Write the electron configuration for the following atoms:
a. B
d. Cl
g. Zn
j. I
b. Ne
e. Ca
h. As
c. Al
f. Sc
i. Rb
7. Which of the following subshells do not exist?
a. 2p b. 1p c. 2d d. 3d e. 3f
8. Identify the atoms which have the following electron configurations:
a. [Ne]3s23p1
b. [Ar]4s2
c. [Ar]4s23d5
HW #2.9
1. Draw an orbital diagram for the following atoms:
a. Mg
b. Ar
c. Rn
2. Which of the following electron configurations corresponds to an atom in its
ground state? Which could be formed if one or more electrons were
excited to higher energy sublevels? Which are impossible?
a. 1s22s22p4
d. 1s22s12p2
2
2
3
1
b. 1s 2s 2p 2d
e. 1s22s22p1
c. 1s22s22p33s1
f. 1s22s3
3. How many total orbitals are filled in the following atoms? a. Ar b. Zn
4. In what group(s) of the periodic table do all the elements have:
a. 2 valence electrons
b. 5 valence electrons
c. 6 valence electrons
5. Identify the atoms that have the following valence electron configurations:
a. 3s23p3
b. 4s1
c. 6s26p5
d. 5s25p4
6. Give the number of electrons in each of the 3p orbitals in each element
from Al through Ar.
e.g.  _ _ 3p = 2, 1, 1
7. Give the total number of half-filled orbitals in atoms which have the
following electron configurations:
a. [Ar]4s23d3
b. [Ar]4s23d5
c. [Ar]4s23d7
8. Write the electron configurations for the following ions:
a. K+
b. Fc. O2d. Al3+ e. Zn2+ f. Pb2+
9. What is unique about the electron configurations of the noble gases and
what bearing does this have on their chemical properties?
10. Give the symbols of three atoms and/or ions which are isoelectronic.
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HW #2.10
Diagram the atomic structure of the following elements by completing a-h below:
1. fluorine
4. neon
2. sulfur
5. aluminum
3. magnesium
6. nitrogen
List the following for each element (see example below):
a. atomic number
b. mass number
c. number of protons, neutrons, and electrons
d. the energy levels, sublevels, and orbitals that the electrons occupy by writing
the electron configuration
e. orbital diagram (can be drawn horizontally across the page)
f. the valence electron structure by writing the Lewis dot symbol
g. the number of electrons the atom would want to gain or lose to become stable
h. the valence/charge of the ion
Example:
Potassium K
a. 19 b. 39
e. 
1s
f. K.
c. 19 p+, 20 n0, 19e-

   
2s
2p
3s
g. lose 1 e
h. +1 (K+)
d. 1s22s22p63s23p64s1
  
3p
__
4s
HW #2.11
1. What was Mendeleev’s system for ordering the elements in his table?
2. What part of Mendeleev’s early periodic table eventually provided it with great creditability?
3. How are the elements ordered in the modern periodic table? Who is credited
with the modern Periodic Law?
4. What causes elements in the same column of the periodic table to have similar
chemical and physical characteristics?
5. Where do you find the elements called
a. alkali metals?
d. the actinide series?
g. transition metals?
b. halogens?
e. the lanthanide series?
h. inner transition metals?
c. noble gases?
f. alkaline earth metals?
i. rare earth metals?
6. What would be the atomic number of the element that completes the 7th
period? What group would it be in?
7. What is the charge/valence of the ions formed by the elements in group: a. 1 b. 2 c. 17
8. Name several characteristic properties of the:
a. noble gases
b. halogens
c. alkali metals d. alkaline earth metals
9. List five uses of halogens.
10. Why are the alkali metals so reactive? Why is lithium the least reactive?
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HW #2.12
1. Classify each of the following statements as true or false.
a. The physical properties of Ti are expected to be intermediate between those of Sc and V.
b. The formula of the chloride of Ti is expected to be the same as those of Sc and V.
c. The formula of the oxide of Ti is expected to be the same as those of Zr and Hf.
d. There are fewer metallic elements than nonmetallic elements.
e. Metalloids lie along a diagonal line which runs from the upper right to the lower left.
2. List four general ways in which metals differ from nonmetals.
3. What is an alloy? Provide two examples of alloys.
4. Explain what is meant by a "periodic" property.
5. Why do the elements show a decrease in size as one proceeds across a period? Why
do the elements show an increase in size as one proceeds down a group?
6. Place the following atoms in order of increasing size: S, Rb, K, C, O, Al, P
7. What happens to the size of an atom when it loses an electron? Gains an electron?
8. Place the following atoms and ions in order of increasing size: Cl, Cl-, Mg, Mg2+
9. Which element is the most common in the universe?
10. What is characteristic of all the elements after #92?
11. What important chemical process happens on stars? What causes stars to shine?
12. What are synthetic elements? How are they formed?
13. What is the difference between a nuclear reaction and a chemical reaction?
HW #2.13
1. If calcium had been chosen as the standard for the relative atomic mass scale and
assigned a value of 10.0 amu, what would be the relative atomic mass of oxygen?
2. What is the mass (with correct units) of one single atom of nickel?
3. List the atomic mass and the molar mass (with correct units) of each of
the following elements:
a. Fe
b. Na
c. P
d. W
4. How many atoms of beryllium would it take to have a mass of 27.0 amu?
5. If a single Si atom has a mass of 28.1 amu, how many Si atoms would have to be
placed on a balance before it would register 28.1 g?
HW #2.14
Use the factor-label method to solve the following problems. Show your units and
the identity of the substance. Cancel units that you have converted. It would be
valuable to estimate your answers before you solve the problem. Round final
answer according to sig figs.
1. Calculate the number of moles of:
a. aluminum atoms represented by a 6.40 g aluminum bottle cap.
b. silver atoms are represented by a 51.0 g silver coin.
c. sodium atoms represented by 1.65 x 1023 sodium atoms.
2. Calculate the number of grams of:
a. helium gas represented by 1.23 mol of helium.
b. gold represented by 0.0022 mol of gold.
c. magnesium represented by 3.45 x 1023 atoms of magnesium.
3. Calculate the number of:
a. atoms represented by 0.400 mol of carbon.
b. atoms represented by 15.0 g of lead.
4. If Arnold Schwarzeneggar is lifting a barbell containing 4.0 x 10 27 iron
atoms, how many pounds is he lifting?
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Selected Answers:
1.a. 0.237 mol Al
b. 0.473 mol Ag
2.a. 4.92 g He
b. 0.43 g Au
3.a. 2.40 x 1023 atoms C
HW #2.15
1. What is the mass of 2.58 x 1022 atoms of nickel?
2. How many atoms are there in 0.789 mol of sodium?
3. How many atoms are there in 15.0 g of potassium?
4. If you have 10.0 g pieces of gold, copper, and silver, which piece would have the
most atoms in it? *try without calculation
5. What is the mass of 9.03 x 1023 atoms of each of the elements K and S.
6. What is the mass of one atom of mercury (in amu and grams)?
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