1. science
2. chemistry

CYCLE 6
Developing Ideas
ACTIVITY 3: Elements and the Periodic Table--
KEY
Purpose
You might imagine that with more than 92 elements, scientists have
developed classification schemes (besides just gas, liquid, and solid as in
Cycle 5) to group elements according to the similarities and differences in
their physical properties and chemical changes.
In fact, early scientists devised a simple classification system for the two
major types of elements—metals and nonmetals—and later came to include a
third type of element, metalloids (also called semimetals). In this activity you
will investigate the physical properties and chemical changes of a small
number of elements in order to duplicate this simple classification system for
elements.
By the late 1800s, scientists had developed an early version of the periodic
table of the elements—a more complex classification scheme based on trends
in certain physical properties and chemical interactions of elements. In this
activity we will use similar information to that which was available in the late
1800s to create our own periodic table of the elements. In the next activity we
will examine how atom structure relates to the modern periodic table.
How are elements classified?
Collecting and Interpreting Evidence
Experiment #1: How can physical properties and chemical interactions
distinguish between metals, nonmetals, and metalloids?
In this activity you will examine the appearance, conductivity, malleability,
and chemical interactions (sometimes called reactivity) of various elements.
© 2007 PSET
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Cycle 6
You will need:
an assortment of elements from the list: carbon (coal and graphite
forms), iron, magnesium, silicon, sulfur, tin, zinc; a pea-sized lump or
~1 cm if using wire or ribbon
3.0 M Hydrochloric acid solution in dropper bottle
1.0 M Copper (II) chloride solution in dropper bottle
Small hammer
Conductivity apparatus
Magnifying glass
Well plates, 2
Forceps/tweezers
CAUTION: Wear safety glasses or goggles.
CAUTION: Do NOT handle any element samples with your fingers—use forceps or
wear gloves to ensure that your skin is not contaminated by these materials.
CAUTION: Be sure to follow standard safety rules for using acids. Do NOT use or
store magnesium ribbon around open flames.
STEP 1. Place a sample of each element in a separate well on your well plate.
Observe the appearance of each element.
Record the appearance of each element in the table below. Include
descriptions of color, luster (shiny or dull), and form—crystalline form
(like table salt), noncrystalline form (like baby powder), or metallic form
(like stainless steel).
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Activity 3: Elements and the Periodic Table
Table 1. Element Properties
Element
Appearance
Conductive
Malleable
Interacts with
Hydrochloric
Acid
Interacts with
Copper
Chloride
Carbon (coal)
Black, noncrys
no
brittle
none
none
Carbon
yes
brittle
none
none
Iron
Gray, noncrys-metallic
looking
Silvery, metallic
yes
malleable
bubbles
turns color
Magnesium
Silvery, metallic
yes
malleable
bubbles
turns color
Silicon
yes
brittle
none
none
Sulfur
Silvery, noncrys-metallic
looking
Yellow, noncrys
no
brittle
none
none
Tin
Silvery, metallic
yes
malleable
bubbles
turns color
Zinc
Silvery, metallic
yes
malleable
bubbles
turns color
(graphite)
STEP 2. Test each element sample with the conductivity
apparatus. If the bulb or diode lights or flashes, electricity is
being conducted through the sample and the sample is
considered conductive.
Record the results of the conductivity test in the table.
STEP 3. Tap each element sample with a small hammer.
(Note: you may want to transfer each element sample from the
well plate to a clean sheet of paper for gentle hammering, and
then return the element to its original well.) If the sample is
malleable, it will flatten or change shape without
shattering when struck by the hammer. If the sample
shatters when struck, it is considered to be brittle.
Record the results of the malleability test in the table.
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Cycle 6
STEP 4. Divide each element sample in half, transferring half of each sample
to a new well. Half of each sample will be used to test the interaction with an
acid, the other half for the interaction with copper chloride.
STEP 5. Add 15-20
drops of hydrochloric
acid solution to each
well containing half of
each element sample.
Use the magnifying
glass to make careful
observations of each
sample.
What evidence do you have that a chemical interaction occurs for some
of the elements?
Bubbles form
Record the results of the hydrochloric acid test in the table.
STEP 6. Add 15-20
drops of copper chloride
solution to each well
containing the other half
of each element sample.
Use the magnifying
glass to make careful
observations of each
sample over 3-5 minutes.
Changes may be slow.
What evidence do you have that a chemical interaction occurs for some
of the elements?
Elements change colors
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Activity 3: Elements and the Periodic Table
Record the results of the copper chloride test in the table.
Which properties tested were physical properties? Which properties
tested involved chemical interactions? Explain your reasoning.
Appearance, conductivity, malleability were physical—could be observed/measured
without changing composition; interaction with hydrochloric acid and copper chloride were
chemical—they involved chemical changes (evident by bubbles forming, or color change,
or formation of black solid)
Sort the elements into two groups—metals and nonmetals—based on
their physical properties and chemical interactions. List the elements in
each group.
Metals: iron, magnesium, tin, zinc
Nonmetals: carbon (coal), sulfur
What physical properties and chemical interactions do most of the
metals exhibit? Which do most of the nonmetals exhibit?
Metals: shiny, silvery appearance; conductive; malleable; interactions with hydrochloric
acid and copper chloride
Nonmetals: dull, noncrystalline appearance; nonconductive; brittle; no interactions with
hydrochloric acid and copper chloride
Which element(s) could belong to either group? Explain your reasoning.
Silicon and graphite—have appearance and conductivity properties like metals but
chemical properties like nonmetals
Exloration #2: How can physical properties and chemical interactions be
used to organize the elements?
How did Dmitri Mendeleev organize the elements?
In 1869 Dmitri Mendeleev (a Russian chemistry teacher) published what is
recognized to be the first periodic table--his model for organizing the
elements that were known in his day. A reproduction of Mendeleev’s
periodic table is shown below. As you examine the table, think about and
answer the questions.
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Cycle 6
What are some organizational features of Mendeleev’s table?
Columns (groups) and rows (periods)
What do you think the letters, numbers, and blanks represent?
Letters: abbreviations of names (chemical symbols); numbers: atomic mass/weight;
blanks: undiscovered elements
How do you think he organized the elements (i.e. why did he choose the
order that he did?)
Increasing atomic mass/weight
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Activity 3: Elements and the Periodic Table
Mendeleev’s Periodic Table was the first to demonstrate “periodic” trend
patterns when melting or boiling points and specific heat values were
graphed against “atomic weight” (at that time, a very crude estimate of the
average mass of an atom of an element, also called relative atomic mass) for 60
elements. He also considered the periodicity of chemical interactions—the
“combining power” (we’ll discuss later), the ratios of elements in compounds
formed, and the reactivity (e.g. with water, air, or metals). His Periodic table
was even able to predict the presence and properties and interactions of
elements that had not yet been discovered.
How will we organize the elements?
In this activity you will create your own periodic table using element cards
containing information similar to that available to Mendeleev. Your goal is to
organize the elements in a way that makes sense of element properties and
chemical interactions.
You will need:
Element cards
Element card sort mat (to be distributed by instructor at STEP 2)
Modern Periodic Table (to be distributed by instructor at STEP 5)
STEP 1. Remove the element cards from the pack. Find Lithium, Beryllium,
Magnesium, Calcium, and Strontium, and Boron. Arrange them according to
the figure below.
STEP 2. Carefully study this
arrangement, making mental
note of some of the patterns
that you observe. Arrange
the remaining cards around
these, using the information
provided on the cards to
guide
your
organizing
strategies.
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Cycle 6
As you work, record your ideas for organizing the cards in the space
below. The objective is not necessarily coming to a “right” answer, but
rather to utilize emerging patterns to develop strategies in this process
of solving a problem.
Did your group have spaces or holes in your element card organization?
Participate in a class discussion and share your organizing strategies.
STEP 2. Your instructor will now distribute the element card sort mat. This
mat most closely resembles Mendeleev’s Periodic Table, but with some
additions and deletions. Compare your organization of the element cards
with the element card sort mat.
How is your organization similar? How is it different?
STEP 3. Rearrange your cards to match the organization shown on the
element card sort mat. As you examine this new arrangement of the element
cards, think about and answer the following questions.
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Activity 3: Elements and the Periodic Table
List as many patterns as you can find that occur horizontally.
Left to right trends: atomic number increases, atomic mass increases, combining power
increases from 1-4 then decreases from 4-1, the ratio of Cl to element increases to 1-3,
the ratio of H to element decreases from 4-1, conductivity is > 1 for metals and metalloids
and extremely low (<< 1) for nonmetals
List as many patterns as you can find that occur vertically.
Top to bottom trends: atomic number increases, atomic mass increases, combining
power is the same for a column, melting/boiling pt decreases for columns 1-4,
melting/boiling pt increases for columns 5-8, density increases, hardess decreases
(softness increases), reactivity increases for columns 1-6 but decreases for columns 7,
for columns 7 and 8 conductivity decreases.
At room temperature, what physical state are most of the elements in?
Solid metals
Where are most of the gases located on the periodic table?
Right side, to the right of the metalloids
Where are the metals located on the periodic table? The nonmetals?
What divides them?
The metalloids divide metals and nonmetals. Metals are to the left of the metalloids,
nonmetals are to the right of the metalloids.
Where are the most highly reactive elements located on the periodic
table? The least reactive elements?
Column 1 increasing down the group and Column 7 decreasing going down the group.
What do you notice about the differences in relative atomic mass
between calcium and gallium, and between strontium and indium? How
does this compare to the differences in relative atomic mass between
other elements such as nitrogen and oxygen, or sodium and
magnesium?
Calcium and gallium/strontium and indium have a difference of ~20. The other elements
differ by ~2-3.
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Cycle 6
Mendeleev left blanks on his periodic table because he did not “force” the
known elements to fit any preconceived pattern. These blanks allowed him
to make predictions of the chemical and physical properties of undiscovered
elements, which guided the search for these new elements.
STEP 4. Compare the element cards with Mendeleev’s Periodic Table. Think
about and answer the questions.
Mendeleev’s periodic table has blanks for __=68 and __=72. Make
careful comparisons in the arrangements of both tables. What element
does __=68 correspond to in your element cards? (Remember, his atomic
masses were very crude estimates!)
Gallium
Are there elements in Mendeleev’s periodic table with atomic masses
between those of calcium and gallium (Mendeleev’s __=68), and
between strontium and indium? If so, where did Mendeleev put them?
Yes. He put 10 elements between calcium and gallium, in rows 4 and 5. He put 10
elements between strontium and indium, in rows 6 and 7. He put four in group 8, and
one of those same elements he put in group 8 is also put in group 1.
Where might you put these additional elements in the element cards?
Explain your reasoning.
If we made a big gap between columns 2 and 3, we could put ten elements across.
STEP 5. Your instructor will now distribute the modern periodic table.
Compare the element cards and Mendeleev’s periodic table to the modern
periodic table. Think about and answer the questions.
Where are the additional elements found in the modern periodic table?
Explain your reasoning.
Ten columns between Group 2A and Group 3A.
Would you expect these elements to be gases, liquids, or solids? Why?
Solid metals, since they are left of the metalloids.
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Activity 3: Elements and the Periodic Table
Your element cards and the modern periodic table include a vertical
column (8A) of inert (nonreactive) gases. Why might Mendeleev not
have included any of the inert gases in his table?
If they are colorless, odorless, and nonreactive, how would he have known that they
existed? He probably had no way to detect them.
According to the modern Periodic Table, what element corresponds to
the blank between gallium (Mendeleev’s __=68) and arsenic in
Mendeleev’s Periodic Table?
Germanium
In the space below, create an element card that predicts the properties
and chemical interactions of this element.
Students should come up with something like:
Moderately hard/soft, gray solid
Metalloid
Density: ~5 g/cm3
Melting point: ~1200-1300 K
Boiling point: ~ 3000-3100 K
Conductivity: responses may vary
Reacts very slowly with oxygen
Forms GeH4 gas
Combining power: 4
atomic mass: ~73
The Periodic Table
Each vertical column on the periodic table is known as a group, or family, of
elements that have similar physical and chemical properties. A number has
been assigned to each group. The elements included in the eight groups in
your card sort are considered representative elements. They are often given
group numbers of 1A-8A, or in Roman numerals IA-VIIIA, increasing from
left to right across the modern periodic table. The elements in the ten groups
in the center of the modern periodic table are the transition elements and are
designated with the letter “B” after their group number. Each horizontal row
is known as a period. The number of the period increases from top to bottom
on the modern periodic table. Notice that the number of elements in a period
increases going down the table. While Mendeleev used groups and periods
in his original periodic table, it wasn’t until scientists better understood atom
structure that they could make full use of these organizational schemes.
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Cycle 6
The metals and nonmetals are divided by a “stairstep” line. The metals are to
the left of the line and the nonmetals are to the right of the line. The elements
that border the line on either side (except for aluminum) are metalloids (also
called semimetals).
There are several named groups of representative elements:
Group 1A (IA): The alkali metals are soft shiny metals, good conductors of
heat and electricity, and have relatively low melting and boiling points.
Elements in this group interact quite vigorously with water, and form white
waxy products when they interact with oxygen. Even though it is at the top of
Group 1A, hydrogen is not considered an alkali metal. It is often positioned
above the alkali metals because of similarities in atom structure, as we will
see in Activity 4.
Group 2A (IIA): The alkaline earth metals have similar properties to the
alkali metals except that they are not as reactive.
Group 7A (VIIA): The halogens are all nonmetals. These elements, especially
fluorine and chloride, are very reactive and form compounds with most of
the elements. When halogens react with metals, they form salts. For example,
when sodium and chlorine interact, they form sodium chloride.
Group 8A (VIIIA): The noble gases are nonreactive and hardly ever combine
with other elements. Vibrant colors are visible when electric current is passed
through some noble gases, but they are colorless at ambient (room)
conditions.
The lanthanide series and actinide series (also known as “rare earth”
elements) are often considered families because they are found together in
minerals and share so many common properties that they are often difficult
to separate and distinguish from one another. They are a special set of
transition elements, are silvery grey shiny metals that tarnish quickly in air,
and are highly conductive.
Summarizing Questions
Discuss these questions with your group and note your ideas. Leave
space to add any different ideas that may emerge when the whole class
discusses their thinking.
S1. In Exploration #2 you predicted the properties and interactions of
germanium, an element that was undiscovered in Mendeleev’s day
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Activity 3: Elements and the Periodic Table
but predicted in his Periodic Table. The card below lists the
properties and interactions of germanium:
moderately soft, silvery white solid
_______________________
density at 298K:5.323 g/cm3
melting point: 1211 K
boiling point: 3093 K
conductivity: 60 W m-1K-1
Germanium, Ge
atomic mass: 72.60
reacts very slowly with oxygen in air
forms GeH4 gas
combining power: 4
(a) How do your predictions compare to the information listed on the
card?
(b) Imagine that you and your classmates experimentally determined
that it germanium did not react with hydrochloric acid or copper
chloride solutions. Would you classify Germanium as a metal,
nonmetal, or metalloid? Explain your reasoning.
Metalloid, it has physical properties of metals, but chemical properties of nonmetals.
S2.
In the space below, create an element card that predicts the properties
and interactions for Cesium, Cs (atomic mass 132.9).
Students should be able to deduce something like the following:
extremely soft, silvery solid
metal
density at 298K:> 1.5 g/cm3
melting point: 295-305 K
boiling point: 900-940 K
conductivity: 30-40 W m-1K-1
Cesium, Cs
atomic mass: 132.9
reacts explosively with oxygen in air
forms CsCl solid
combining power: 1
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Cycle 6
You may wish to have students perform a web search to find the exact quantities for density,
melting point, boiling point, and conductivity (given below). The following site is an adequate
reference. http://www.webelements.com/webelements/elements/text/Cs/key.html
S3. Do elements in vertical columns of the Periodic Table generally have
similar
or
different
properties
and
interactions?
What
evidence/examples do you have?
Similar: some elements are reactive with oxygen or with metals but to varying degrees,
elements in a column form compounds with same ratios and have same combining
power
S4. Do elements in horizontal rows of the Periodic Table generally have
similar
or
different
properties
and
interactions?
What
evidence/examples do you have?
Different: reactivities differ greatly, compound ratios and combining power change from
element to element, physical properties (appearance, harness, melting/point,
conductivity, etc.) may differ greatly from element to element
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