Download Periodicity and Predictions of Properties

Periodicity and Predictions of Properties
Objectives1
1.
2.
3.
4.
To become familiar with the organization of the periodic table.
To study periodic properties.
To make predictions based on periodic properties.
To use the periodic table to assist in writing chemical formulas.
Discussion
The periodic law states that many properties of the elements are periodic functions of their atomic
numbers. A periodic function is one which goes through cycles, with maximum and minimum values at regular
intervals. The atomic radius, melting point, and boiling point are periodic properties of the elements. The periodic
table arranges the elements in order of increasing atomic number in such a way that the periodic nature of
properties is made clear. This is done by placing in the same vertical column of the table those elements that
appear at corresponding positions in the cycle of properties. For example, since the atomic radii of Li, Na, K, Rb,
and Cs appear at maxima in the cycles for atomic radii as a function of atomic number, we would expect that
these elements would be in the same column in the periodic table. These elements belong to a family, or Group,
and have many other properties which would also indicate that they should be classified together. In general,
properties of the elements in a Group tend to change gradually as one goes from the lightest to the heaviest atom
in the group. Within the framework of the periodic table properties vary according to a pattern as you move across
the table in a cycle, or period, or up and down one of the Groups. If the pattern for the variation is known, it is
often possible to predict a property of one element from the properties of elements which lie nearest that element
in the table. Depending on the position of the element in the table, the best prediction will either be based on
elements in the same row, or on elements in the same column, as the element for which the prediction is to be
made.
In this experiment you will make some graphs of periodic properties versus atomic number in order to
discover the patterns the properties follow. You will then use those patterns to predict some properties of
elements. In the last part of the experiment you will be asked to assign elements to their proper positions in the
table on basis of their characteristic properties.
Procedure
1. Using the data in Table 1, plot the atomic radius of each element on the y-axis against its atomic number on
the x-axis. Make the x-axis on the long side of the paper and choose the scales so that all data will fit on the
sheet. Connect all points to make a line graph. Label each peak with the symbol of the element.
2. Ionization Energy – If you want to remove an electron from an atom a certain amount of energy is needed.
The amount of energy needed varies among atoms and is called ionization energy. This energy is needed to
overcome the attraction between the electron and the nucleus of the atom. It is called ionization energy
because the result is an ion or positively charged atom. It is typically measured in kJ/mol.
Organize the data in Table 2 Ionization Energies, and then graph the atomic number of the element (on the
horizontal axis) versus the ionization energy (on the vertical axis). Connect all points to make a line graph.
Think about the scale you will use.
3. Electronegativity – Atoms have different abilities to attract electrons to themselves when they are bonded in
a compound or molecule. The measure of this ability to pull an electron to an atom within a compound or
molecule is referred to as electronegativity. A bonded atom with a higher electronegativity can pull stronger
on an electron with a weaker electronegativity.
1
Adapted from Periodicity and Predictions of Properties in Chemistry Masterton, Slowinski and Walford. Holt, Rinehart
and Winston publishers (1980) by Ema Gluckmann 10/04; modified 11/10
1
Organize the data in Table 3, and then graph the atomic number of the element (on the horizontal axis)
versus the electronegativity (on the vertical axis). Connect all points to make a line graph. Think about the
scale you will use.2
4. Fill in the blanks in the periodic table provided you by your teacher with the letter symbol for each of the
mystery elements whose properties are described. The idea is to identify the mystery element and to put its
symbol in the proper place in the blank table. In doing this part of the experiment you may use the periodic
table in your text and any information in the text.
(a) A, B, C, and D belong to a family, the members of which are all gases. A is commonly used in
advertising signs. B was first discovered on the sun and is used in weather balloons. C was used to make
the first compounds of an element of this group. D is the family member that is present in the largest
amount in air.
(b) E and F are members of a family containing both gaseous and solid elements. E forms a diatomic
molecule and is the major constituent of the atmosphere. Element F is a dangerous poison and a
metalloid.
(c) G, H, and I belong to family of very active metals, all of which react with chlorine to produce salts with
the general formula XCl. G is a member of the first period to contain 18 elements. H has the highest
ionization energy of the family and I has the lowest.
(d) J, K, and L belong the same family and all are metals. A compound of J is a major component of bones
and teeth. K is commonly used in flash bulbs for producing light. L is a radioactive element discovered by
Marie Curie.
(e) M is a gas and has some properties similar to the elements in both Group 1 and Group 7. It is a unique
element in this respect.
(f) N, O, and P commonly form -1 ions when they combine with metals. N is a liquid and O is a nonradioactive solid. P is the most chemically reactive of all the non-metals.
(g) Q, R, S, and T are in different families but in the same period. Q is a gas used for water purification. R is
a yellow non-metallic solid. S is a metalloid used in transistors. T is a metal of low density used in aircraft
construction.
(h) U, V, W, and X are all transition elements. U is an excellent conductor of heat and electricity and is
commonly used in wiring and cookware. V is the only metal that is a liquid at room temperature. W is the
metal which is produced in the largest quantity. Although once used in coins, X is now used mostly in
expensive jewelry.
(i) Y is an actinide fuel used in nuclear reactors. Z is the actinide named for the “father” of the Periodic
Table.
Calculations and Questions
1. (a) Describe any regularity that is present in the graph of atomic radius versus atomic number. Which
elements occupy the peaks in the cycles? Are the periods, or cycles, of the same length?
(b) In Table 1 the atomic radii of Mg and Fe were left blank intentionally. The values are actually known, but
you should be able to predict them based on the pattern of properties on the graph. Note that the part of
cycle from Li (3) to B (5) is repeated in the part of the cycle from Na (11) to Al (13). We would expect,
then, that the radius of Mg would have a value that would maintain the pattern observed between Li and
B. On that basis, predict the radius of the Mg atom.
(c) As part of the last cycle on the graph, which starts at K (19), we have the first series of transition metals.
By assuming that the Fe (26) atom would maintain the pattern set by atoms near it in atomic number,
predict the radius of the Fe atom.
2. For the graphs you constructed in Procedures 2 and 3 describe any patterns you see in the graphs. Are these
properties periodic properties? Explain any patterns you observe; i.e. explain the reason behind them.
2
Sacramento Area Science Project; An Education Partnership; UC Davis and CSU Sacramento; http://sasp.ucdavis.edu
2
3. Using the periodic table prepared in Procedure 4, predict the formulas for compounds of the following
elements: (Use these mystery letters in the formulas.)
(a) M and P
(c) E and M
(e) A and G
(b) T and Q
(d) I and R
(f) J and N
In predicting the formulas you may find the following formulas of known substances to be useful:
AlBr3
HCl
PH3
Li2O
BaCl2
NaI
4. Ionic radius. Atoms become ions when electrons are gained or lost. Table 4 compares some parent ions with
their daughter cations or anions.
a. What do you see is the general trend for when an atom loses electrons (becomes a cation)? What is the
explanation for this phenomenon?
b. What do you see is the general trend for when an atom gains electrons (becomes an anion)? What is the
explanation for this phenomenon?
Table 1 Atomic radii of the elements in nm (10-9 m)
Element
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
Atomic
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Atomic
radius
0.037
0.050
0.152
0.111
0.088
0.077
0.070
0.066
0.064
0.070
0.186
--0.143
0.117
0.110
0.104
0.099
0.094
Element
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Atomic
number
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Atomic
radius
0.231
0.197
0.160
0.146
0.131
0.125
0.129
--0.125
0.124
0.128
0.133
0.122
0.122
0.121
0.117
0.114
0.109
Table 2 Ionization energy of representative elements (kJ/mol)
Atomic
Number
1
3
11
19
4
12
20
21
22
23
24
25
Ionization
Energy
1312
520
496
419
900
738
590
633
659
651
653
717
Atomic
Number
26
27
28
29
30
5
13
31
6
14
32
7
Ionization
Energy
762
760
737
746
906
801
578
579
1086
787
762
1402
3
Atomic
Number
15
33
8
16
34
9
17
35
2
10
18
36
Ionization
Energy
1012
947
1314
1000
941
1681
1251
1140
2372
2081
1521
1351
Table 3 Electronegativity values of representative elements
Atomic
Number
1
3
11
19
4
12
20
21
22
23
24
25
Electronegativity
2.1
1.0
0.9
0.8
1.5
1.2
1.0
1.3
1.5
1.6
1.6
1.5
Atomic
Number
26
27
28
29
30
5
13
31
6
14
32
7
Electronegativity
1.8
1.8
1.8
1.9
1.6
2.0
1.5
1.6
2.5
1.8
1.8
3.0
Atomic
Number
15
33
8
16
34
9
17
35
2
10
18
36
Electronegativity
2.1
2.0
3.5
2.5
2.4
4.0
3.0
2.8
3.0
Table 4 Atomic and ionic radii of various representative elements in nm (10-9 m)
Element
H
Li
Be
N
O
F
Na
Mg
P
Cl
Atomic
number
1
3
4
7
8
9
11
12
15
17
Atomic
radius
0.037
0.152
0.111
0.070
0.066
0.064
0.186
0.160
0.110
0.099
Ion
HLi+
Be2+
N3O2FNa+
Mg2+
P3Cl-
Ionic
radius
0.154
0.078
0.034
0.130
0.140
0.133
0.102
0.072
0.212
0.181
Conclusion: Write out a conclusion for this lab describing what you learned about periodic trends of
the various properties studied.
This is a blank
periodic table that
you may fill in, cut
out, and attach to
your lab notebook
for procedure 4a-i
4