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Unit 1. Materials: Formulating Matter
B. Periodic Trends. How can the periodic table be used to help explain and predict the properties of
chemical elements?
More than 100 chemical elements have been discovered and explored. Of those, a small number are considered
highly prized and used for coins, jewelry, and art. Why are some more valuable than others? How do scientists
classify and organize the characteristics of the elements? In this section, you will examine properties of some
elements and construct statements about groups of elements and their reactivity. As you study the ideas in this
section, think about how the periodic table could help you to explain the use of certain elements in forms of
currency.
Elements are arranged in the periodic table based on their properties. Elements with similar chemical
properties are placed in the same columns. Physical properties vary in predictable patterns across
rows and down columns.
1. Give another term for these features of the periodic table.
a. Row
b. Column
2. Give the names and symbols of two elements other than lithium in the alkali metal family.
3. Consider the noble gas family.
a. Where are they located on the periodic table?
b. Name one physical property that they share.
c. Name one chemical property that they share.
4. Do you expect carbon, C, to be more similar to nitrogen, N, oxygen, O, or silicon, Si? Why?
5. The element krypton (Kr) was not known in Mendeleev’s time. Given that the boiling
point of argon (Ar) is -186˚C and of xenon (Xe) is -112˚C, estimate the boiling point of
krypton.
Ar
bp -186°C
Kr
Xe
bp -112°C
6. Estimate the melting point of rubidium (Rb). The melting point of potassium (K) and cesium (Cs) are 337K
and 302K, respectively. (Hint: show how the elements are arranged in the periodic table.)
7. Would you expect the melting point of sodium (Na) to be higher or lower than that of rubidium (Rb)?
Explain.
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8. The melting points of sulfur (S) and tellurium (Te) are 115°C and 450°C, respectively. Estimate the melting
point of selenium (Se).
9. Mendeleev knew that silicon tetrachloride (SiCl4) existed. Using his periodic table, he correctly predicted
the existence of ekasilicon, an element just below silicon on the Periodic Table. Predict the formula for the
compound formed by Mendeleev’s ekasilicon (now called germanium, Ge) and chlorine.
10. Here are formulas for some known compounds: NaBr, MgCl2. Predict the formula for a compound formed
from
a. K and Br
c. Ca and Cl
b. Na and Cl
d. Mg and I
11. Here are formulas for some known compounds: CaO, Al2O3. Predict the formula for a compound formed
from
a. Mg and O
c. Mg and S
b. B and O
d. Ga and S
12. Suppose you have equal amount of calcium, Ca, in two beakers. You react the calcium in one beaker with
oxygen, O, and the other with sulfur, S. The reaction with oxygen forms the compound calcium oxide,
CaO.
a. What do you predict is the chemical formula of the compound formed from the reaction between
calcium and sulfur?
b. Which compound has more mass, the compound containing calcium and oxygen, or the compound
containing calcium and sulfur? Explain your thinking.
Building Skills: Properties and Uses of Copper.
13. Consider the uses of copper shown below. For each use, identify
those particular properties that make copper an appropriate.
choice. Use the table to the right as reference.
Uses of Copper
Properties of Copper
Malleability and ductility
High
Electrical conductivity
High
Thermal conductivity
High
Resistance to corrosion
High
Useful alloys formed
Bronze, brass, etc.
Color and luster
Reddish, shiny
Properties Required for Use
Electrical
Plumbing
Coins
Jewelry
Pots and Pans
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14. How would increased recycling of scrap copper affect future availability of copper?
Is there a limit to the role copper recycling can play? (In other words, can we fill all our copper needs
through recycling?) Why?
15. For each use below, describe a technological change that could decrease the demand for copper:
a. Coins
b. Communications
c. Power generation
d. Indoor electrical wiring
The Electrical Nature of Matter
16. What force do the following pairs of particles experience: attraction (A), repulsion (R), or none (N)?
a. proton, proton
c. neutron, proton
b. proton, electron
d. electron, electron
Counting Subatomic Particles: Atoms and Ions
An atom is composed of smaller particles (protons, neutrons, and electrons), each possessing a
17.
characteristic mass and electrical charge. The number of protons in an atom of a given element
18.
distinguishes it from atoms of all other elements. Atoms containing the same number of protons
19.
but different numbers of neutrons are considered isotopes.
20.
17. For each element, identify the number of protons or electrons needed for an electrically neutral atom.
a. carbon:
b. aluminum:
c. lead:
d. chlorine:
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protons
____
electrons
____
protons
13
electrons
82
protons
____
protons
_____ electrons
17
electrons
3
18. Decide whether each of these atoms is electrically neutral and, if not, calculate the net charge.
a. chlorine:
17 protons
18 electrons
Neutral? _____
Charge: ______
b. cobalt:
27protons
24 electrons
Neutral? _____
Charge: ______
c. gold:
79 protons
76 electrons
Neutral? _____
Charge: ______
d. strontium:
38 protons
36 electrons
Neutral? _____
Charge: ______
e. argon:
18 protons
18 electrons
Neutral? _____
Charge: ______
19. Complete the table below for each electrically neutral atom.
Element Name
a. hydrogen
Element
Symbol
Number of
Protons
Number of
Neutrons
Number of
Electrons
H
1
0
1
b. sodium
12
c.
d.
5
B
e.
f.
5
6
115
Pa
77
140
20. How is the atom in 15c different from that in 15d?
21. A scientist announces the discovery of a new element. The only characteristic given in the report is the
element’s mass number of 266. Is this information sufficient, by itself, to justify the claim of the
discovery of a new element? Explain.
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POGIL Chemical Formulas and Names of Ionic Compounds
WHY?
Going back to pre-historic times, humans have experimented with chemical processes that helped them to
make better tools, pottery and weapons. In the middle-ages, alchemists combined various compounds in the
search for the philosopher’s stone and the elixir of life. However, as chemistry became a real science,
chemists realized that all mater was made of atoms and that chemical processes were simply a rearrangement
of these atoms. Chemists needed some simple, shorthand way to show this fact, and thus created chemical
formulas.
Model 1: An atomic look at three compounds
The diagrams below represent some ionic compounds at the atomic level.
Name: Sodium chloride
Na+ Cl- Na+ Cl- Na+ ClCl- Na+ Cl- Na+ Cl- Na+
Na+ Cl- Na+ Cl- Na+ Cl-
Calcium chloride
Cl-
Cl-
Cl-
Cl-
Aluminum oxide
Cl-
Ca2+ Ca2+ Ca2+ Ca2+ Ca2+
Cl-
Cl-
Cl-
Cl-
Cl-
O2-
O2-
O2-
Al3+ Al3+ Al3+ Al3+
O2-
O2-
O2-
Chemical formula:
NaCl
CaCl2
Al2O3
22. How does the name of the elements in each compound differ from that of the individual elements when
they are not combined with other compounds?
23. How many sodium ions are there in the sodium chloride sample shown above? __________ How many
chloride ions are there in the sodium chloride sample shown above? _________ What is the simplest,
whole number ratio between sodium and chlorine in sodium chloride? Na:Cl =
____________________
24. How many calcium ions are there in the calcium chloride sample shown above? __________ How
many chloride ions are there in the calcium chloride sample shown above? __________ What is the
simplest, whole number ratio between calcium and chlorine in calcium chloride? Ca:Cl =
_______________
25. What is the simplest, whole number ratio between the aluminum and oxide ions in aluminum oxide?
26. What is the relationship between the chemical formula for the compounds above and the ratio of the ions
in them?
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27. What is the electrical charge of one sodium ion in sodium chloride? __________ What is the electrical
charge of one chloride ion in sodium chloride? __________
28. All samples of sodium chloride have a ratio of one sodium ion for one chloride ion. What must be true of
the total (net) charge for any crystal of sodium chloride?
29. What is the electrical charge of one calcium ion in calcium chloride? __________ What is the electrical
charge of one chloride ion in calcium chloride? __________
30. All samples of calcium chloride have a ratio of one calcium ion for two chloride ions. What must be true
of the total (net) charge for any sample of calcium chloride?
31. From the pattern seen in the last two questions, what is the rule for the total charge for any ionic
compound?
I32. Write the chemical formula for the compound depicted here:
I-
I-
I-
I-
Ba2+ Ba2+ Ba2+ Ba2+ Ba2+
I-
I-
I-
I-
I-
Model 2: Ionic Charges
Many ions have the same charge whenever they are found in a compound. Some of these ions are listed in
the table below.
Group:
Charge:
1
+1
2
+2
13
+3
15
-3
16
-2
17
-1
Lithium
Li+
---
---
Nitride
N3
Oxide
O2
Fluoride
F
Sodium
Na+
Magnesium
Mg2+
Aluminum
Al3+
Phosphide
P3
Sulfide
S2
Selenide
Se2
Calcium
Ca2+
Rubidium
Rb+
Cesium
Cs+
Barium
Ba2+
---
---
---
---
Bromide
Br
---
33. What patterns do you notice about the charges of the ions formed, compared to the location of the
element in the Periodic Table?
34. Use your own Periodic Table to fill in the gaps in the table above (ignore the cells with ---).
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Neutral Ionic Compounds
The size of each shape below represents the relative amount of charge on an ion. Cations (positive ions) and
anions (negative ions) combine to make neutral compounds; some charge combinations are shown below.
[An ionic compound almost always contains only one kind of cation and one kind of anion, so compounds
like NaKO and CaClBr do not normally exist.]
Ion shapes showing magnitude of ion charge:
1+
2+
1-
2-
B
Neutral combinations:
3+
D
C
A
E
3-
F
35. Simple Ionic Compounds. Give the simplest neutral compound that results from each combination of
ions, and choose the letter (A-F) that matches the arrangement of ions.
Ions
a. Mg2+ + Cl-
Compound
Arrangement
MgCl2
C
Ions
Arrangement
e. Na+ + S2-
b. Li+ + Cl-
f. Ca2+ + O2-
c. K+ + N3-
g. Al3+ + Br-
d. Mg2+ + S2-
h. Ba2+ + Cl-
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Compound
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36. Harder Ionic Compounds. Try the crossover trick for these compounds: the magnitude (size) of the
charge on each ion becomes the subscript for the other ion. Check that the formula is electrically neutral
by multiplying each ionic charge by its subscript. When added together, the sum should equal zero.
Don’t forget that the cation goes first and be sure to reduce the subscripts to give a ratio with the
smallest whole numbers! [For example, Ca2O2 simplifies to become CaO]
Ions
a. Al3+ + O2-–
Compound
A Al3+ + O2- = Al O
2 3
l
Total positive
charge
2  (3+) = +6
Total negative
charge
3  (2) = -6
Net charge
0
3
b. Ca2+ + N3–
+
+
c. O2– + Ni4+
O
2
d. Cr3+ + S2–
e. Se2- + Fe3+
3–
f. P + Ti
2+
-
=
A
l
2
O
37. Polyatomic Ions.
A polyatomic ion is a group of atoms that, as a group, carries an electrical charge.
3
There are many negatively-charged polyatomic ions, but the only polyatomic ion with a positive charge
is NH4+.
When a polyatomic ion occurs two or more times in a formula, its formula is placed inside parenthesis
and the number of ions are shown as a subscript after the parenthesis.
Ions
a. Fe2+ + OH-
Compound
Total positive
charge
Total negative
charge
Net charge
Fe(OH)2
1  (2+) = +2
2 × (1-) = -2
0
b. Pb2+ + SO32-
c. NH4+ + CO32-
d. Na+ + PO43-
e. Cr3+ + SO42-
f. Ba2+ + PO43106736747
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38. Fill in the data table for each ionic compound described below. Number one is filled in as an example.
Use the two tables of common ions below.
a. Potassium chloride is “lite salt”, used by many people with hypertension.
b. CaSO4 is a component of plaster.
c. A substance composed of Ca2+ and PO43- ions is found in some forms of phosphorus-containing
fertilizer. This substance is also a major component of bones and teeth.
d. Ammonium nitrate, a rich source of nitrogen, is often used in fertilizer mixtures.
e. Al2(SO4)3 is a compound that can be used to help purify water.
f.
Magnesium hydroxide is called milk of magnesia when it is mixed with water.
g. Limestone and marble are two common forms of the compound calcium carbonate.
h. Baking soda is sodium, hydrogen carbonate.
Cation
a.
K+
Anion
Cl–
Formula
KCl
Name
Potassium chloride
b.
c.
d.
e.
f.
g.
h.
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39. More Practice.
Cation
Anion
Formula
a.
Calcium oxide
b.
c.
NaCl
NH4+
NO3–
d.
Cu(OH)2
e.
Iron(III) sulfate
K+
f.
SO32–
g.
h.
Na3PO4
Pb2+
Br–
i.
j.
Lead(II) carbonate
Al3+
PO43–
k.
Magnesium hydrogen carbonate
l.
m.
Name
K2S
Ba2+
SO42–
n.
o.
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Zinc phosphate
FeCl3
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Trends in Metal Reactivity
Use the following metal activity series and a periodic table to answer these questions. Remember that the most
active metals tend to end up as ions, combined with other substances.
Metal Activity Series
Element
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Manganese
Zinc
Chromium
Iron
Lead
Copper
Mercury
Silver
Platinum
Gold
most
active
least
active
Metal Ion(s) Found
in Minerals
Li+
K+
Ca2+
Na+
Mg2+
Al3+
Mn2+
Zn2+
3+
Cr , Cr2+
Fe3+, Fe2+
Pb2+
Cu2+, Cu+
Hg2+
Ag+
Pt2+
Au2+, Au+
Processes Used to obtain the Metal
Pass electricity through molten mineral
(electrometallurgy)
Heat mineral with charcoal or carbon
monoxide (CO) (pyrometallurgy)
Heat mineral in air (pyrometallurgy) or
find the element free
State of Metal
Obtained
Li(s)
K(s)
Ca(s)
Na(s)
Mg(s)
Al(s)
Mn(s)
Zn(s)
Cr(s)
Fe(s)
Pb(s)
Cu(s)
Hg(s)
Ag(s)
Pt(s)
Au(s)
40. a. What trend in metallic reactivity is found from left to right across a horizontal row (period) of the
Periodic Table? Hint: compare the reactivities of Na, Mg, Al.
b. In which part of the PT are the most reactive metals found?
least
c. Which part of the PT contains the least reactive metals?
active
41. a. Will iron metal (Fe) react with a solution of lead(II) nitrate, Pb(NO3)2?
b. Will platinum metal (Pt) react with a lead(II) nitrate solution?
c. Explain your answers to Questions 20a. and 20b.
42. Which of these reactions is most likely to occur? Why?
a. Calcium metal with chromium(III) chloride solution
b. Chromium metal with calcium chloride solution
43. Consider these two equations. Which represents a reaction that is more likely to occur? Why?
a. Zn2+(aq) + 2 Ag(s)  Zn(s) + 2 Ag+(aq)
b. 2 Ag+(aq) + Zn(s)  2 Ag(s) + Zn2+(aq)
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