When Mendeleev started his work, how many elements were known at that time? 

Key Points

• 63 elements were known when Mendeleev started his work on the periodic table.
• Mendeleev's periodic table was revolutionary because he organized the elements based on their atomic mass and predicted the existence and properties of new elements.
• His periodic table allowed for the prediction of the properties of elements that had not yet been discovered.
• Mendeleev's work laid the groundwork for the modern periodic table, which is based on atomic number rather than atomic mass.

Additional Information

• Dmitri Mendeleev was a Russian chemist who is best known for creating the Periodic Table of Elements.
• He arranged the 63 known elements into a table based on atomic mass, which revealed that elements with similar properties occurred at regular intervals.
• Mendeleev left gaps in his periodic table for elements that were not yet discovered, confidently predicting their properties and atomic masses.
• These gaps were later filled with the discovery of elements such as gallium and germanium, which confirmed the accuracy and utility of Mendeleev's periodic table.
• The modern periodic table is arranged by increasing atomic number, which is the number of protons in an atom's nucleus, rather than atomic mass.
• Mendeleev's periodic law states that the properties of elements are a periodic function of their atomic masses.