MODULE 2
9
WORKSHEET
WORKSHEET
CONSTRUCTING A
PERIODIC TABLE
Syllabus reference 8.3.3
INTRODUCTION
A century ago chemical knowledge was much less advanced than it is today. Only two-thirds of the
elements known today had been identified and their atomic masses were uncertain. Likewise the
formulae of many of their compounds had not yet been established. Chemists at the time were looking
for patterns and relationships between the elements and this culminated in the periodic table.
The purpose of this exercise is to place you in a similar position to early chemists in their search
for regularities. You have been supplied with a data sheet (see overleaf) listing most of the elements
discovered by 1869, their then accepted atomic masses and a few other properties. Use the graph
paper on the following page to complete the exercises.
Copyright © 2008 McGraw-Hill Australia
CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 9
DATA SHEET
ELEMENT
Hydrogen
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Sodium
Magnesium
Aluminium
Silicon
Phosphorus
Sulfur
Chlorine
Potassium
Calcium
Titanium
Vanadium
Chromium
Manganese
Iron
Nickel
Cobalt
Copper
Zinc
Arsenic
Selenium
Bromine
Rubidium
Strontium
Yttrium
Zirconium
Niobium
Molybdenum
Rhodium
Ruthenium
Palladium
Silver
Cadmium
Indium
Tin
Antimony
Iodine
Tellurium
Cesium
Barium
SYMBOL
ATOMIC
WEIGHT2
(1869)
DENSITY
(g/mL)
ATOMIC
VOLUME
HYDROGEN
COMPOUND
H
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Ti
V
Cr
Mn
Fe
Ni
Co
Cu
Zn
As
Se
Br
Rb
Sr
Y
Zr
Nb
Mo
Rh
Ru
Pd
Ag
Cd
In
Sn
Sb
I
Te
Cs
Ba
1
7
9.4
11
12
14
16
19
23
24
27.4
28
31
32
35.5
39
40
50
51
52
55
56
59
59
63
65.2
75
79.4
80
85.4
87.6
88?
90
91
96
104.4
104.4
106.8
108
112
113?
118
122
127
128?
133
137
—
0.53
1.8
2.5
2.26
—
—
—
0.97
1.74
2.70
2.4
1.82
2.07
—
0.86
1.55
4.5
5.96
7.1
7.2
7.86
8.90
9.0
8.92
7.14
5.7
4.7
3.12
1.53
2.6
5.51
6.4
8.4
10.2
12.5
12.2
12
10.5
8.6
7.3
5.8
6.0
4.93
6.1
1.90
3.5
—
13
5.2
4.4
5.3
—
—
—
24
14
10
12
17
15
—
45
26
11
8.6
7.3
7.6
7.1
6.6
6.5
7.1
9.1
13
17
26
56
34
16
14
11
9.4
8.3
8.5
8.9
10
13
16
20
20
26
21
70
39
H2
LiH
BeH2
B2H6
CH4
NH3
H 2O
HF
NaH
MgH2
AlH3
SiH4
PH3
H 2S
HCl
KH
CaH2
NOTES:
1 Classes of elements are based on their conductivities:
M = metal,
N = non-metal
2 ‘Atomic weight’ is relative atomic mass on a scale on which
in 1869 the mass of the hydrogen atom was taken as 1.
Copyright © 2008 McGraw-Hill Australia
CuH
ZnH2
AsH3
H2Se
HBr
RbH
SrH2
CdH2
InH3
SnH4
SbH3
HI
H2Te
CsH
BaH2
VALENCY
CLASS1
MELTING
POINT (°C)
1
1
2
3
4
3
2
1
1
2
3
4
3
2
1
1
2
—
—
—
—
—
—
—
1
2
3
2
1
1
2
—
—
—
—
—
—
—
—
2
3
4
3
1
2
1
2
N
M
M
N
N
N
N
N
M
M
M
N
N
N
N
M
M
M
M
M
M
M
M
M
M
M
N
N
N
M
M
M
M
M
M
M
M
M
M
M
M
M
N
N
N
M
M
?3
180
1280
2030
3500
?3
?3
?3
98
650
660
1410
44
113
?4
64
838
1670
1900
1900
1250
1540
1450
1490
1083
419
613
217
–7
39
770
1500
1850
2420
2610
1970
2300
1550
961
321
156
232
631
114
450
29
714
3 The elements H, N, O and F were known only as gases
in 1869.
4 The melting point of chlorine Cl was unknown, though its
boiling point (–34.7°C) was known.
CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 9
MATERIALS:
❍ graph paper
Part 1: Physical properties
1
In 1869 the masses of the atoms of the elements were not known. But they did know the relative
atomic masses which they recorded on a scale based on hydrogen = 1. This was called the atomic
weight of the element.
They also knew the density of many elements. From this they could calculate the relative atomic
volume using the ratio:
atomic weight
atomic volume 
density
This gave a rough indication of the relative sizes of atoms. The calculation has been done on the data
sheet.
On the graph paper plot a graph of atomic volume versus atomic weight for the elements on the list.
Join the points in order of atomic weight.
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MODULE 2 WS 9
2
Do the atomic volumes gradually increase or rise and fall at intervals?
Rise and fall at intervals
3
a
Identify the elements forming the five main peaks on the graph.
Li, Na, K, Rb, Cs
b
From the data sheet are these five classified as metals or non metals?
Metals
c
Check the melting points of these five elements on the data sheet. Do they posses any similarity
in this property?
Li 180ºC, Na 98ºC, K 64ºC, Rb 39ºC, Cs 29ºC
Melting points decrease as atomic volume increases and atomic weight increases.
Part 2: Chemical properties
1
The data sheet gives the formula of the simplest compound that each element forms with hydrogen
(blank spaces indicate no known true compound). The valency of an element may be thought of
as the number of hydrogen atoms which will combine with one atom of that element. Using this
definition, calculate the valency of each element (where possible) and insert in the data sheet.
H 1, Li 1, Be 2, B 3, C 4, N 3, O 2, F 1, Na 1, Mg 2, Al 3, Si 4, P 3, S 2, Cl 1, K 1, Ca 2,
Cu 1, Zn 2, As 3, Se 2, Br 1, Rb 1, Sr 2, Cd 2, In 3, Sn 4, Sb 3, I 1, Te 2, Cs 1, Ba 2
2
Using these values, construct a valency versus atomic weight graph on the grid below for the first
17 elements listed.
Valency
4
3
2
1
H
3
a
Li
Be
B
C
N
O
F
Na Mg
Al
Si
P
S
Cl
K
Ca
Does valency vary periodically (like atomic volume)?
Yes, it varies periodically.
b
Is there any relationship between the valencies of the five related elements in Part 1?
Valencies of Li, Na, K, Rb and Cs are all 1.
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MODULE 2 WS 9
Part 3: A periodic table
1
As well as a graph, the valency relationships may be represented on a table. The chart has been
constructed into vertical columns (Groups I, II etc) and horizontal rows (Periods 1, 2 etc).
2
The element hydrogen has been positioned in Group I of Period 1. Transfer the symbols for the next
seven elements on the data sheet into Period 2, starting from the left-hand side.
3
Repeat the process with the next seven elements and Period 3.
Periodic table of elements known in 1869
I
1
II
III
IV
V
VI
VII
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
As
Se
Br
Rb
Sr
Sb
Te
I
Cs
Ba
H
2
Period
3
III
IV
V
VI
VII
VIII
I
II
B
B
B
B
B
B
B
B
Cu
Zn
4
5
Cd
In
Sn
6
4
Examine the groups to which the elements have been allocated so far and tabulate them.
Group
number
Valency of
elements
5
I
II
III
IV
V
VI
VII
1
2
3
4
3
2
1
Transfer the next two elements from the data sheet to the start of Period 4. Does the vertical
valency relationship still hold true?
Yes
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MODULE 2 WS 9
6
a
Looking vertically, list the three elements so far allocated to Group I.
Li, Na, K
b
List the five related elements from Part 1 (3).
Li, Na, K, Rb, Cs
c
d
If a connection is assumed which element should begin:
i
Period 5
Rb
ii
Period 6
Cs
Is the valency relationship still valid?
Yes, all have a valency of 1.
7
a
b
Following the pattern, which two elements should be placed in Group II of:
i
Period 5
Sr
ii
Period 6
Ba
Do the valencies match the other members of Group II?
Yes, all have a valency of 2.
8
a
From the data sheet list which element precedes the one at the start of Period 5?
Br
b
Assuming this element belongs to Period 4, logically it should be assigned to Group VII. Is this
consistent in terms of valency?
Yes, Group VII elements have a valency of 1.
9
Now position the two elements preceding this one in Period 4. Do their valencies fit the pattern?
Yes, Group VI elements have a valency of 2 and Group V elements have a valency of 3.
10 a
Continue backwards along Period 4, which element is next in the list?
Zn
b
What is its valency?
2
c
Does it belong in Group IV? Explain.
No elements in Group IV have a valency of 4 but Zn has a valency of 2.
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d
Counting down the data sheet we see that at first similar elements occur in every seventh place
(e.g. Li, Na, K; Be, Mg, Ca) but after calcium the next similar element, Sr, is 14 places away.
This suggests that there must be additional places in the fourth period as shown in the blank
table. These are annotated with a B to identify them.
A better position for the problem element in part a is then in Group IIB, thus indicating its
valency. Which element would then fit into IB?
Cu
This locates all the elements of known valency in Period 4 but leaves gaps in Groups III and IV.
11 It should be possible to partially complete Period 5 by starting at the right end and working
backwards as was done with Period 4.
a
From the data sheet which element, from its atomic weight, should fit into Period 5 Group VII,
Te
i.e. the one before Cs? _______________
b
2
What is its valency? _______________
c
Yes
Does it fit better into Group VI rather than Group VII? _______________
d
I
Which element should go into Group VII? _______________
12 Proceed in the direction of decreasing atomic weight as with Period 4 to complete all the squares in
Period 5 for those of known valency. Check for consistency.
13 You should now have positioned all 31 elements (not counting hydrogen) on the basis of their
valencies.
Part 4: A prediction using the table
1
The table has blank spaces for unknown elements X (Group III) and Y (Group IV) in Period 4.
a
What evidence is there in the atomic weight sequence on the data sheet for undiscovered
elements in this region?
There should be other elements because the atomic weight sequence jumps to a much
higher value.
b
2
Predict the formula for the simplest hydrogen compound of:
i
X
XH3
ii
Y
YH4
It is possible to make predictions about the atomic weight of X and Y by averaging the atomic
weights of elements either side of them. What do you predict the atomic weight of X and Y to be?
The atomic weights of the two missing elements average to 70. One will therefore be less
than 70 and one will be more than 70. Possible values are 68 and 72.
Although not complete, some generalisations can be made from the table you have constructed.
The process you have followed is similar to the process used by Mendeleev and Lothar Meyer in
developing the first periodic table.
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 9