Which physical and chemical properties of the elements were used by Mendeleev in creating his periodic table ? List two observation which posed a challenge of Mendeleev's periodic law.
Which physical and chemical properties of the elements were used by Mendeleev in creating his periodic table ? List two observation which posed a challenge of Mendeleev's periodic law.
Mendeleev’s periodic table was based on the fact that: “The properties of elements are the periodic functions of their atomic weights."
The observations which posed a challenge are:
1. Position of hydrogen
Hydrogen resembles alkali metals (forms H+ ion just like Na+ ions) as well as halogens ( forms H− ion similar to Cl− ion).The position of hydrogen was not correctly defined. It was placed in Group I although its properties resembled both the Group I elements (the alkali metals) and the group VII elements (the halogens).
2. Position of isotopes
Different isotopes of same elements have different atomic masses, therefore, each one of them should be given a different position in the periodic table. On the other hand, because they are chemically similar, they had to be given same position.
3. Anomalous pairs of elements
At certain places, an element of higher atomic mass has been placed before an element of lower atomic mass. For example, Argon (39.91) is placed before potassium (39.1)
Mendeleev’s periodic table was based on the fact that: “The properties of elements are the periodic functions of their atomic weights."
The observations which posed a challenge are:
1. Position of hydrogen
Hydrogen resembles alkali metals (forms H+ ion just like Na+ ions) as well as halogens ( forms H− ion similar to Cl− ion).The position of hydrogen was not correctly defined. It was placed in Group I although its properties resembled both the Group I elements (the alkali metals) and the group VII elements (the halogens).
2. Position of isotopes
Different isotopes of same elements have different atomic masses, therefore, each one of them should be given a different position in the periodic table. On the other hand, because they are chemically similar, they had to be given same position.
3. Anomalous pairs of elements
At certain places, an element of higher atomic mass has been placed before an element of lower atomic mass. For example, Argon (39.91) is placed before potassium (39.1)
