Mendeleev's periodic table was based on increasing atomic...

Name: Problem 42, Chapter 4: Chemistry
Uploaded: 2021-05-20T02:54:24-08:00
Duration: 40 s
Channel: Nicole Smina
Description: Mendeleev's periodic table was based on increasing atomic weight. Argon has a higher atomic weight than potassium, yet in the modern table argon appears before potassium. Explain how this can be.

Mendeleev's periodic table was based on increasing atomic weight. Argon has a higher atomic weight than potassium, yet in the modern table argon appears before potassium. Explain how this can be.

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Key Concepts

Atomic Number vs. Atomic Weight

Atomic weight is an average mass of the atoms of an element, whereas atomic number is the count of protons in an atom's nucleus. The modern periodic table organizes elements by increasing atomic number because this ordering accurately reflects the sequential filling of electron shells and the underlying electronic structure, which determines chemical properties. Consequently, despite having a higher atomic weight, argon appears before potassium because its atomic number is lower.

Periodic Law

The periodic law states that the properties of the elements are periodic functions of their atomic numbers. This observation underpins the structure of the modern periodic table and allows elements with similar chemical behaviors to be grouped together. By arranging elements based on atomic number instead of atomic weight, the table now consistently aligns with observed chemical periodicity, resolving earlier discrepancies such as the one involving argon and potassium.

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