Question

What was Henry Moseley’s major contribution to the periodic table and what year was it?

Answer 1

Hint: Periodic table is an arrangement of elements discovered to date in a tabular form that is used to analyze the properties of elements. There were many attempts made by different scientists in history to arrange the elements in a proper manner. But in the 19th century, Henry Moseley introduced the concept of atomic number in the periodic table which was found to be the most accurate arrangement.

Complete answer:
Chemists have always looked for ways of arranging the elements to reflect the similarities between their properties. The periodic table is a tabular organization of elements that shows the periodicity in the properties of elements. Scientists use the table to analyze, predict and, understand properties of different elements and speculate on the properties of those yet to be discovered.
Several scientists worked to assemble the elements into a proper format. Antoine Lavoisier was the first who determined similarity in properties of certain elements. He tried grouping the elements as metals and nonmetals.
Forty years later, German physicist Wolfang Dobereiner arranged the elements in groups of three in increasing order of atomic weight and called them triads. It was observed that some properties of the middle element, such as atomic weight, are the average value of the other two elements in each triad.
Then, in 1864 John Newlands arranged the elements into a table in which every eight elements had similar properties. This was known as the law of octaves. He left no gaps for undiscovered elements.
In 1869, Russian chemist Dmitri Mendeleev came up with the periodic law which stated that properties of elements are periodic functions of their atomic masses. He created a periodic table in which elements were arranged in increasing order of their atomic masses and he left gaps for elements that were yet to be discovered. The later discovery of elements predicted by Mendeleev verified his predictions.
But there were several discrepancies in Mendeleev’s periodic table. In 1913, English physicist Henry Moseley correlated the properties of elements to their atomic numbers. He then rearranged the elements in the periodic table on the basis of atomic numbers and it was found that this resolved the disparities in earlier forms of the periodic table that were based on atomic masses.
Hence, in 1913 Henry Moseley made a major contribution to the periodic table by arranging elements in increasing order of atomic numbers.

Note:
There are only 7 groups and 6 periods and no place for isotopes is allotted in Mendeleev’s periodic table. While Moseley’s periodic table has 18 groups, 7 periods and isotopes are kept in the same place as the atomic numbers of isotopes are the same.