1. CHAPTER 4 : PERIODIC TABLE OF ELEMENTS
Chemistry
Form 4
CHAPTER 4 : PERIODIC TABLE OF ELEMENTS
4.1 The Periodic Table of Elements
Prepared by:
KUMARI PARONJODI

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Chemistry
Form 4
Historical Development
PERIODIC TABLE
OF ELEMENTS
Arrangement
Relationship
Question
Advantages
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3. Historical Development of Johann W. Dobereiner (1780-1849)
Chemistry
Form 4
Historical Development of
The Periodic Table
Antoine Lavoisier ( )
Historical
Arrangement
Johann W. Dobereiner ( )
Relationship
John Newlands ( )
Advantages
Lothar Meyer ( )
Questions
Dmitri Mendeleev ( )
H. J. G. Moseley ( )

4. Antoine Lavoisier (1743-1794) Chemistry Form 4 Historical
A French chemist, was the first person to classify elements into groups.
In the year 1789, the known elements at that time were classified into four groups as shown in table 1.
In his table, elements were classified into metals and non-metals.
Classification by Lavoisier was unsuccessful because his table consisted of many wrong information. For example, light, heat and a few compound which were unable to be decomposed at that time such as lime, silica, alumina, barita and magnesia were considered as elements.
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5. Table 1 Classification of the elements by Lavoisier
Chemistry
Form 4
Group 1
Group 2
Group 3
Group 4
Oxygen
Nitrogen
Hydrogen
Light
Heat
Sulphur
Phosphorus
Carbon
Chlorine
Flourine
Arsenic
Bismuth
Cobalt
Lead
Zinc
Nickel
Tin
Silver
Lime
Silica
Alumina
Barita
Magnesia
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Table 1 Classification of the elements by Lavoisier

6. Johann W. Dobereiner (1780-1849)
Chemistry
Form 4
Johann W. Dobereiner ( )
In the year 1829, Johann W. Dobereiner, a German chemist, divided the elements into groups. Each group consisted of three elements with similar chemical properties. He named each of these groups as triad.
In each triad, the relative atomic mass of the middle element was approximately the average relative atomic mass of the other two elements. Two examples of triads are shown in table 2.
Classification of the elements into triads by Dobereiner was unsuccessful because this classification was limited to a few elements only.
However, this Triad Law had awakened other chemist to realise that there was a relationship between the chemical properties and the atomic mass of the elements.
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7. Lithium Sodium Potassium
Chemistry
Form 4
Elements in triad
Lithium Sodium Potassium
Average relative atomic of lithium and potassium
= ( 7+39 ) / 2
= 23
Relative atomic mass
Chlorine Bromine Iodine
Average relative atomic of chlorine and iodine
= ( ) / 2
= 81
Table Triad
Questions
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8. John Newlands (1837-1898) Chemistry Form 4
In the year 1863, John Newlands, a British chemist, arranged all the known elements according to the ascending order of their atomic masses.
Table 3 shows part of the arrangement of the elements suggested by Newlands.
Historical
Arrangement 1 2 3 4 5 6 7 H Li Be B C N O F Na Mg Al Si P S Cl K Ca Cr Ti Mn Fe
Co,Ni Cu Zn Y In As Se Br Rb Sr
Ce,Ia Zr
Di,Mo
Ro,Ru Pd Ag Cd U Sn Sb Te
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Table 3 Arrangement of the elements by Newlands

9. Chemistry
Form 4
He found that the same properties were repeated at every eight element in his arrangement. This pattern was similar to the octave notes in music. This arrangement of elements was known as the Law of Octaves.
Contribution by Newlands failed because his Law of Octaves was obeyed by the first 17 elements only.
His contribution is important because he is the first chemist to show the existence of a periodic pattern for the properties of elements.
The periodic repetition of the properties of elements was used as a basis for further developments of the Periodic Table.
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10. Lothar Meyer (1830-1895) Chemistry Form 4
In the year 1870, Lothar Meyer, a German chemist, plotted a graph of the atomic volume against the atomic mass for all the known elements as in figure 1. (The atomic volume of an element is the volume of one mole atom of that element).
He realised that elements with similar chemical properties occupied the same relative positions on the atomic volume curve.
For example:
Li, Na, K, Rb and Cs (alkali metals) located at the maximum points of the curve have similar chemical properties.
F, Cl, Br and I (halogens) located at the slopes of the curve also have similar chemical properties.
Meyer was successful in showing that the properties of the elements were in a periodic pattern with their atomic masses.
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11. Figure 2 Atomic volume curve
Chemistry
Form 4
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Figure 2 Atomic volume curve

12. Dmitri mendeleev (1839-1907) Chemistry Form 4 Historical Arrangement
A Russian chemistry professor, had shown that the properties of elements changed periodically with their atomic masses.
In the year 1869, he arranged the elements in the same way as Newlands but made a few changes as below.
a) elements with similar chemical properties were placed
in the same column called group.
b) empty spaces were left in the Periodic Table for those
undiscovered elements at the time.
c) he made use of the positions of elements in the Periodic
Table to predict the properties of undiscovered elements at
that time. Table 4 shows the comparison of the properties
of ‘Ekasilicon’ as predicted by Mendeleev with the properties
of germanium that was discovered in the year 1886.
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13. Chemistry Form 4 Property Ekasilicon (Es) Germanium (Ge) Atomic mass
Table 4 Prediction of properties of germanium by Mendeleev
Property
Ekasilicon (Es)
Germanium (Ge)
Atomic mass 72
72.6
Colour of metal
Grey
Density
5.5 g/cm³
5.47 g/cm³
Formula of oxide
EsO2
GeO2
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d) He mutually changed the positions of two pairs of elements, that were nickel (atomic mass = 58.7) with cobalt (atomic mass = 58.9) and iodine (atomic mass = 126.9) with tellurium (atomic mass = 127.6) so that the elements with similar chemical properties were placed under the same group.
Questions

14. Chemistry
Form 4
e) Arranged certain elements such as manganese, iron, cobalt and nickel in separate groups.
These groups of elements were known as
transition elements.
His Periodic Table was used as the basis for the formation of the Periodic Table today.
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15. H. J. G. Moseley (1887-1915) Chemistry Form 4 Historical
In the year 1914, H. J. G. Moseley, a British physicist, investigated the X-ray spectrum of elements.
He plotted a graph of the square root of the frequency of X-ray from the elements against their proton numbers. A straight line was obtained.
The proton numbers should be used as a basis for the periodic changes in the chemical properties of elements.
Therefore, Moseley arranged the elements in increasing order of their proton numbers. He produced a Periodic Table similar to Mendeleev’s Periodic Table.
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16. Chemistry
Form 4
In Moseley’s Periodic Table, he confirmed that tellurium (Te) must be placed before iodine (I) and cobalt (Co) must be placed before nickel (Ni) as predicted by Mendeleev.
Hence, Moseley was successful in developing the Periodic Table based on the arrangement of elements in ascending order of their proton numbers.
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17. Arrangement of Elements in
Chemistry
Form 4
Arrangement of Elements in
the Periodic Table
Figure 3 Shows the Periodic Table.
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18. Chemistry
Form 4
Elements are arranged horizontally in ascending order of their proton numbers in the periodic table.
Each vertical column of elements in the periodic table is known as a group. Elements with the same number of valence electrons are arranged in the same group.
There are 18 vertical columns of elements in the periodic table, known as Group 1, Group 2, Group 3 until Group 18.
Group 1 elements are known as alkali metals. Group 2 elements are known as alkali earth metals. Group 3 to Group 12 elements are known as transition elements. Group 17 elements are known as halogens. Group 18 elements are known as noble gases.
Each horizontal row of elements in the periodic table is known as a period.
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19. Chemistry
Form 4
There are 7 horizontal rows in the periodic table, known as Period 1, Period 2, Period 3 until Period 7.
Period 1 – 2 elements,
Periods 2 & 3 – 8 elements respectively.
Periods 4 & 5 – 18 elements each.
Periods 6 – 32 elements.
Period 7 – 23 elements.
Periods 1 to 3 are short periods while Periods 4 to 7 are long periods.
Although Period 6 contains 32 elements, elements with proton numbers 58 to 71 are listed separately at the bottom of the periodic table. This series of elements is known as lantanides.
Similarly, elements with proton numbers 90 to 103 in Period 7 are listed separately at the bottom of the Periodic Table. This series of elements is known as actinides.
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20. Chemistry
Form 4
Elements in Groups 1, 2 and 13 are metals.
Transition elements in Groups 3 to 12 are also metals.
Non-metals usually have 5, 6 or 7 valence electrons. They are placed in Groups 15, 16 and 17 respectively in the Periodic Table. Carbon and silicon from Group 14 are also non-metals.
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21. Figure 4 Elements with proton numbers 1 to 20
Chemistry
Form 4
Relationship Between the electron
Arrangement and the Position of the
Element in the Periodic Table
Historical
Based on Figure 4, we can deduce that the number of valence electrons in an atom of an element determines the position of the group of that element in the Periodic Table.
Arrangement
Group 1 18
Period 11 1H 2 13 14 15 16 17
2He 22
3Li
4Be 5B 6C 7N 8O 9F
10Ne 33
11Na
12Mg
13Al
14Si
15P
16S
17Cl
18Ar 44
19K
20Ca
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Figure Elements with proton numbers 1 to 20

22. Number of valence electrons 1 2 3 4 5 6 7 8 (Except Helium)
Chemistry
Form 4
Remember
For elements with 1 or 2 valence electrons, the group number of that element is equal to the number of valence electrons.
For elements with 3 to 8 valence electrons, the group number of that element is equal to the number of valence electrons plus 10.
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Number of valence electrons 1 2 3 4 5 6 7 8
(Except Helium)
Group 13 14 15 16 17 18
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Table 5 Relationship between the number of valence electrons and the position of the group of an element

23. Chemistry
Form 4
Examples
Element R has a proton number of 16. In which group is element R located in the periodic Table?
Historical
SOLUTION:
Arrangement
Number of electrons in atom R
= number of proton
= proton number
= 16
Electron arrangement of atom R = 2.8.6
Number of valence electrons = 6
Hence, element R is located in Group 16 of the Periodic Table.
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24. Number of shells occupied with electrons 1 2 3 4 5 6 7
Chemistry
Form 4
The numbers of shells occupied with electrons in an atom determines the position of the period of that element in the Periodic Table.
Historical
Number of shells occupied with electrons 1 2 3 4 5 6 7
Period 13 14 15 16 17
Arrangement
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Table 5 Relationship between the number of shells occupied with electrons and the position of the period of an element.
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Hence, the position of the period of an element is equal to the number of shells occupied with electrons in the atom of that element.

25. Chemistry
Form 4
Examples
An atom of element T has 16 neutrons and a nucleon number of 31. In which period is element T located in the periodic table?
Historical
Arrangement
SOLUTION:
Number of electrons in atom T
= number of protons in atom T
= nucleon number – number of neutrons
= 31 – 16
= 15
Electron arrangement of atom T = 2.8.5
Atom T has 3 shells occupied with electrons.
Hence, element T is located in period 3 of the Periodic table.
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26. Chemistry
Form 4
Elements with the same number of valence electron will exhibit similar chemical properties.
Historical
Example:
Arrangement
Atom X with an electron arrangement of and atom Y with an electron arrangement of exhibit similar chemical properties because both atoms have 2 valence electrons.
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27. Advantages Of Classifying Elements
Chemistry
Form 4
Advantages Of Classifying Elements
in the Periodic Table
Historical
Enables chemist to learn and understand physical properties and chemical properties of the elements and compounds more systematically, orderly and easily.
The properties of an element and its compounds can be predicted based on its position in the Periodic Table.
It becomes easier to study and understand the relationship among the elements from different groups.
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28. That's All....... Chemistry Form 4 Historical Arrangement Relationship
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