Name the chemist who proved that the atomic number of an element is a more fundamental property than its atomic mass, which led to modification in Mendeleev's Periodic Law table?
Henry Moseley
Understanding the Fundamental Property of Elements
The question asks to identify the chemist responsible for proving that the atomic number of an element is a more fundamental property than its atomic mass. This discovery was crucial as it led to a significant modification in Mendeleev's Periodic Law and the structure of the periodic table.
Mendeleev's Periodic Law
Dmitri Ivanovich Mendeleev arranged the elements known in his time in a table based on their atomic masses. His Periodic Law stated that the properties of elements are a periodic function of their atomic masses. While this arrangement was revolutionary and allowed for the prediction of unknown elements, it had some inconsistencies. For instance, in some cases, elements with higher atomic masses were placed before elements with lower atomic masses to maintain the grouping of elements with similar properties (e.g., Argon before Potassium, Cobalt before Nickel).
Henry Moseley's Contribution: Atomic Number
In the early 20th century, specifically in 1913, Henry Moseley conducted experiments using X-ray spectroscopy. He studied the characteristic X-rays emitted by different elements when bombarded with high-energy electrons. Moseley found a remarkably regular pattern in the frequencies of these X-rays. He discovered that the square root of the frequency ($\sqrt{\nu}$) of the characteristic X-rays emitted by an element is directly proportional to a whole number that is characteristic of that element. This number was later identified as the atomic number ($Z$), which represents the number of protons in the nucleus of an atom.
Moseley's relationship can be expressed as:
\(\sqrt{\nu} = a(Z - b)\)
Where \(\nu\) is the frequency of the characteristic X-rays, \(Z\) is the atomic number, and \(a\) and \(b\) are constants.
Atomic Number as the Fundamental Property
Moseley's work clearly demonstrated that the atomic number is a more fundamental property of an element than its atomic mass. The properties of an element are determined by the number of electrons (and thus the number of protons or atomic number) which dictate its electronic configuration and chemical behavior. The inconsistencies in Mendeleev's table, where elements were ordered contrary to their atomic masses, were perfectly explained when the elements were arranged according to their atomic numbers.
Modification of Periodic Law
Based on Moseley's findings, the Periodic Law was modified. The Modern Periodic Law states that the properties of elements are a periodic function of their atomic numbers. This revised law is the basis for the modern periodic table, where elements are arranged in increasing order of their atomic numbers, resolving the anomalies present in Mendeleev's original table.
Analyzing Other Options
- Johann Dobereiner proposed the Law of Triads, grouping elements in sets of three based on atomic mass and similar properties, much earlier than Mendeleev.
- John Newlands proposed the Law of Octaves, arranging elements by atomic mass and noting that properties repeated every eighth element. This was also before Mendeleev's major work and the concept of atomic number.
- Dmitri Ivanovich Mendeleev developed the first comprehensive periodic table based on atomic mass. While his contribution was foundational, it was Moseley who identified the atomic number as the more fundamental property that refined Mendeleev's law.
Therefore, Henry Moseley is the chemist credited with proving the atomic number as the fundamental property and leading to the modification of the periodic law.
Revision Table: Key Chemists and Contributions to Periodic Table
| Chemist | Key Contribution | Basis of Arrangement |
|---|---|---|
| Johann Dobereiner | Law of Triads | Atomic Mass (groups of 3) |
| John Newlands | Law of Octaves | Atomic Mass (every 8th element) |
| Dmitri Mendeleev | Periodic Table, Periodic Law | Atomic Mass |
| Henry Moseley | Proved Atomic Number is fundamental, Modified Periodic Law | Atomic Number |
Additional Information on Modern Periodic Table
The modern periodic table arranges elements based on increasing atomic number in periods (rows) and groups (columns). Elements within the same group have similar chemical properties because they have the same number of valence electrons and similar outer shell electronic configurations. The periods represent the filling of electron shells. This arrangement provides a logical and accurate framework for understanding the properties and behavior of elements.
Important Questions from Periodic Table
Which of the following is the most reactive metal?
Which of the following acids is injected into the skin during an ant bite?
Sodium hydroxide is NOT used for________.
Which of the following statements about carbon monoxide is INCORRECT?
Which of the following minerals does NOT fall in the category of non-metallic minerals?
