The History Of the Periodic Table
By 1860 about sixty elements were known and a method was needed for organisation. Many scientists made significant contributions that eventually enabled Dmitri Mendeléev to construct his table.
The Periodic Table is based on the properties of matter. We can describe, identify, separate, and classify all the elements by properties.
There are two types of property of matter. Physical properties which describe the material as it is and chemical properties which describe how an element reacts, with what it reacts, the amount of heat it produces as it reacts, or any other measurable trait that has to do with the power of the element.
The periodic table came about from the idea that we could arrange the elements, originally by atomic weight, in a format that would show similarity among groups.
By studying the elements Lithium, Sodium and Potassium, it can be seen that they react alike with water, oxygen and chlorine to make similar compounds. It was shown that potassium has a higher rate of reaction than sodium and that lithium has a lower rate of reaction than sodium. If you link this with their atomic masses, sodium again is the middle element
Li Na K
6.9 23 39.1
This pattern is repeated with other groups of threes such as, Chlorine, Bromine and Iodine. This became known as the Law of Triads and was discovered by German Chemist Johann Döbereiner.
Johann Döbereiner (1780-1849)
In the early 1817 Johann Döbereiner found that Barium, Calcium and Strontium had very comparable properties. He put these elements together in groups called a triad. He also put the elements in order according to their masses. He found that the middle elements in each group had a mass that is about half way between the other two, such as the example in Lithium, Sodium and Potassium. Döbereiner found several groups of three that worked together in the same way. This was the beginning of looking for trends in the arrangements of elements. This law at the time however was considered being no little more than a curiosity as only a few elements and their masses were actually known.
By 1860 about sixty elements were known and a method was needed for organisation. Many scientists made significant contributions that eventually enabled Dmitri Mendeléev to construct his table.
The Periodic Table is based on the properties of matter. We can describe, identify, separate, and classify all the elements by properties.
There are two types of property of matter. Physical properties which describe the material as it is and chemical properties which describe how an element reacts, with what it reacts, the amount of heat it produces as it reacts, or any other measurable trait that has to do with the power of the element.
The periodic table came about from the idea that we could arrange the elements, originally by atomic weight, in a format that would show similarity among groups.
By studying the elements Lithium, Sodium and Potassium, it can be seen that they react alike with water, oxygen and chlorine to make similar compounds. It was shown that potassium has a higher rate of reaction than sodium and that lithium has a lower rate of reaction than sodium. If you link this with their atomic masses, sodium again is the middle element
Li Na K
6.9 23 39.1
This pattern is repeated with other groups of threes such as, Chlorine, Bromine and Iodine. This became known as the Law of Triads and was discovered by German Chemist Johann Döbereiner.
Johann Döbereiner (1780-1849)
In the early 1817 Johann Döbereiner found that Barium, Calcium and Strontium had very comparable properties. He put these elements together in groups called a triad. He also put the elements in order according to their masses. He found that the middle elements in each group had a mass that is about half way between the other two, such as the example in Lithium, Sodium and Potassium. Döbereiner found several groups of three that worked together in the same way. This was the beginning of looking for trends in the arrangements of elements. This law at the time however was considered being no little more than a curiosity as only a few elements and their masses were actually known.
