INTRODUCTION
Historical Development of The Periodic Table
1. Antoine Lavoisier (1743-1794)
2. Johann W. Dobereiner (1780-1849
3. John Newlands (1837-1898)
4. Lothar Meyer (1830-1895)
5. Dmitri Mendeleev (1839-1907)
6. H. J. G. Moseley (1887-1915)
2. Johann W. Dobereiner (1780-1849
3. John Newlands (1837-1898)
4. Lothar Meyer (1830-1895)
5. Dmitri Mendeleev (1839-1907)
6. H. J. G. Moseley (1887-1915)
Antoine Lavoisier (1743-1794)
- 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.
- 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.
Johann W. Dobereiner (1780-1849)
- 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.
- 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.
John Newlands (1837-1898)
- 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.
- 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.
- 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.
- 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.
Lothar Meyer (1830-1895)
- 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.
- 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.
Dmitri mendeleev (1839-1907)
- 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.
- 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.
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.
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.
H. J. G. Moseley (1887-1915)
- 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.
- 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.
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.
H. J. G. Moseley (1887-1915)
- 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.
- 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.