MODULE 2
10
WORKSHEET
WORKSHEET
TRENDS IN THE PERIODIC TABLE
Syllabus reference 8.3.3
1
Complete the following with a word or phrase to check your understanding.
a
In the nineteenth century, as more elements became known, chemists searched for patterns
in properties. A German chemist, Dobereiner, noticed patterns among the elements involving
triads
several triplets (groups of three elements). He called these _______________.
In 1864 John
octaves
Newlands proposed a ‘law of _______________’
where he arranged the known elements in
weight
groups of eight in order of increasing atomic _______________.
b
Mendeleev
A Russian chemist, Dmitri _______________,
produced the forerunner to the modern
weight
Periodic Table. He arranged the elements in increasing atomic _______________
and placed
properties
elements having similar _______________
under one another to obtain a table. An important
aspect of Mendeleev’s table was the fact that he recognised there were discoveries still to
gaps
properties
be made, so he left _______________
and predicted the _______________
of elements which
could fill the spaces. His work was vindicated when three of his predicted elements were
similar
discovered and their properties were found to be_______________
to his predictions.
c
discrepancies emerged with his table. The discovery of the
As time passed some _______________
noble
column
_______________
gases by William Ramsay added another _______________
to the Periodic
Moseley
Table. Further work by physicist Henry _______________
led to the reorganisation of the
number
Periodic Table based on atomic _______________
rather than atomic weight.
d
groups
The modern periodic table has the elements organised into vertical _______________
and
periods
horizontal _______________.
The table is organised so that elements with similar chemical
group
properties are in the same _______________.
Today we know that it is an element’s electron
configuration which is used to explain its properties.
_______________
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 10
e
decrease
Atomic radii generally _______________
as you go from left to right across a period. Atomic radii
increase
electrons
generally _______________
as you move down a group because there are more _______________.
f
ionisation
The energy required to remove an electron from an atom is called the _______________
increases
energy. This generally _______________
as you move from left to right across a period
decreases
highest
and _______________
as you move down a group. The noble gas has the _______________
ionisation energy within each period.
g
increases
As you remove successive electrons the ionisation energy _______________
but not always
uniformly. The differences between successive ionisation energies shows that atoms tend to
noble
lose electrons to attain the electron configuration of the _______________
gases.
2
a
Complete the table below by inserting the values for atomic number, group number and period.
b
Use the table below to make generalisations about the electrical conductivity and boiling point
across a period and down a group.
ELEMENT
SYMBOL
ATOMIC
NUMBER
GROUP
NUMBER
PERIOD
ELECTRICAL CONDUCITIVITY
(MS m1)
BOILING
POINT (ºC)
Hydrogen
H
1
1
1
—
253
Helium
He
2
8
1
—
269
Lithium
Li
3
1
2
10.6
1342
Beryllium
Be
4
2
2
27
2970
Boron
B
5
3
2
1010
3660
Carbon
C
6
4
2
0.07
4830
Nitrogen
N
7
5
2
—
196
Oxygen
O
8
6
2
—
183
Fluorine
F
9
7
2
—
188
Neon
Ne
10
8
2
—
246
Sodium
Na
11
1
3
21
883
Magnesium
Mg
12
2
3
22
1110
Aluminium
Al
13
3
3
37
2450
3
103
3267
3
1015
280
445
Silicon
Phosphorous
Si
P
14
15
4
5
Sulfur
S
16
6
3
1021
Chlorine
Cl
17
7
3
—
35
Argon
Ar
18
8
3
—
189
Potassium
K
19
1
4
14
760
Calcium
Ca
20
2
4
29
1484
Rubidium
Rb
37
1
5
7.6
39
Cesium
Cs
55
1
6
5.0
28
Francium
Fr
87
1
7
—
27
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 10
i
Identify any trend in electrical conductivity.
Generally electrical conductivity increases then decreases from left to right across a period.
Generally electrical conductivity decreases from top to bottom down a group.
ii Identify any trend in boiling point.
Boiling point generally increases then decreases from left to right across a period and
decreases from top to bottom down a group.
iii Use the graph paper to plot a graph of boiling water vs atomic number for elements in
Group 1.
iv Use the same graph paper and a different colour to plot a graph of boiling point vs atomic
number for Period 2.
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 10
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3
Classify each of these statements as true or false. Rewrite the false statements so they are true.
a
In his periodic table Mendeleev arranged the elements according to increasing atomic number.
FALSE
In his periodic table Mendeleev arranged the elements according to increasing atomic
WEIGHT.
b
The element in Group IV Period 4 is gallium.
FALSE
c
The element in Group IV Period 4 is GERMANIUM.
Removing one electron from an atom results in an ion with a charge of 1+.
TRUE
d
The metallic character increases as you move from left to right and decreases as you move
from top to bottom.
FALSE
The metallic character DECREASES as you move from left to right and INCREASES
as you move from top to bottom.
e
Moving across a period the bonding changes from metallic to covalent.
TRUE
f
The melting points generally rise to the element in Group V then decrease.
FALSE
4
Element W forms the chloride WCl2 and the oxide WO. Element Y is in the same group of the
Periodic Table as W. What would you expect for the formula of the hydroxide and bromide of
element Y?
Y(OH)2
5
The melting points generally rise to the element in Group IV then decrease.
YBr2
a In the Periodic Table how does the atomic radius vary:
b
i across a period from left to right?
decreases
ii down a group from top to bottom?
increases
In each of the following sets place the elements in order of increasing atomic radius:
i potassium, calcium, magnesium
magnesium, calcium, potassium
ii chlorine, argon, silicon
argon, chlorine, silicon
iii gallium, phosphorus, aluminium
phosphorus, aluminium, gallium
iv chlorine, argon, arsenic, bromine
argon, chlorine, bromine, arsenic
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 10
6
The first ionisation energies for sodium, silicon and sulfur are 1.01, 0.50 and 0.79 MJ/mol but not
necessarily in that order. Assign the values to the elements and explain your reasoning.
Ionisation energy increases from left to right so sodium would be 0.50 MJ/mol, silicon would be
0.79 MJ/mol and sulfur would be the highest at 1.01 MJ/mol.
7
The following table lists successive ionisation energies (in kJ/mol) for three elements A, B and C.
a
A
B
C
First ionisation energy
580
502
744
Second ionisation energy
1820
4570
1460
Third ionisation energy
2750
6920
7740
Fourth ionisation energy
11600
9550
10500
Why is the second ionisation energy always greater than the first?
It requires more energy to remove the second electron because this involves removing a negative
electron from a positive ion due to extra electrostatic attraction.
b
Why is there a big jump in value between the second and third energies for C and between the
third and fourth for A?
The jump would mean an electron is being removed from a filled electron shell.
c
What would you expect to be the charges on the ions formed by each of A, B and C?
A3, B1, C2
8
The following diagram summarises some ways in which properties vary across and down the
Periodic Table. Insert the word increases or decreases in the space provided.
decreases
atomic radius
increases
ionisation energy
reactivity of metals
electronegativity
increases
decreases
metallic character
decreases
increases
decreases
increases
decreases
increases
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CONQUERINGCHEMISTRY PRELIM
MODULE 2 WS 10
9
The electronegativity of an element is a measure of its ability to attract electrons. The higher the
electronegativity of an element, the more strongly it attracts electrons. An element’s ability to
attract electrons will have a bearing on whether it forms positive ions, covalent bonds or negative
ions.
The shared pair of electrons in a covalent bond are rarely shared equally between the two atoms
involved. One atom usually has a higher electronegativity than the other and thus attracts the
electrons more strongly. This atom has therefore acquired an extra share of negative charge and
begins to resemble a negative ion. The other atom correspondingly begins to resemble a positive
ion. The extent to which this sharing of an electron pair is unequal is indicated by the percentage
ionic character of a simple bond.
The table below gives the electronegativity of atoms of selected elements. It is arranged in the same
way as a Periodic Table from which the noble gases (helium, neon, argon and krypton) and the
transition elements (scandium to zinc) have also been omitted.
TABLE OF ELECTRONEGATIVITY OF SELECTED ELEMENTS
H
2.1
Li
1.0
Be
1.5
B
2.0
C
2.5
N
3.0
O
3.5
F
4.0
Na
0.9
Mg
1.2
Al
1.5
Si
1.8
P
2.1
S
2.5
Cl
3.0
K
0.8
Ca
1.0
Ga
1.6
Ge
1.8
As
2.0
Se
2.4
Br
2.8
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The graph below shows how the per cent ionic character of a single bond varies according to the
difference in electronegativity between the two elements forming the bond.
100
90
80
70
60
50
40
30
20
10
0
0
1
2
3
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Answer the following questions using the table and graph above.
a
What is the relationship between the per cent ionic character of single bonds and the
electronegativity difference between their elements?
The greater the electronegativity difference the greater the per cent ionic character.
b
What electronegativity difference will result in a bond with a 50% ionic character?
Approximately a 1.5 difference.
c
Estimate the percentage ionic character of bonds formed between:
Difference is 1 so 20–24% ionic character.
i nitrogen and fluorine
ii sodium and oxygen
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Difference is 2.6 so 90–92% ionic character.
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MODULE 2 WS 10