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Question
State the periodic law on which Mendeleev's periodic table table was based. Why and how was this periodic law changed?
Solution
According to Mendeleev's periodic law, the properties of elements are a periodic function of their atomic masses. This means that when elements are arranged in an increasing order of their atomic masses, the elements with similar properties repeat at regular periods.
However, Henry Moseley, a scientist, showed that the atomic number of an element is a more fundamental property and a better basis to classify elements than the atomic mass. The atomic number increases consistently by 1, from one element to the next, whereas the atomic mass does not change regularly. Also, the atomic number of an element does not change and remains fixed. This led to a change in Mendeleev's periodic law.
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RELATED QUESTIONS
The element eka-silicon in Mendeleev’s periodic table is known as ………… in the modern periodic table.
What property do all elements in the same column of the Periodic Table as fluorine have in common?
In Mendeleev's periodic table, why was there no mention of noble gases like helium, neon and argon?
Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his periodic table?
In Mendeleev's periodic table, gap was not left for one of the following elements. This element is:
(a) gallium
(b) beryllium
(c) germanium
(d) scandium
In Mendeleev's periodic table, gaps were left for the elements to be discovered later on. An element which found a vacant place in the periodic table later on is:
(a) Be
(b) Si
(c) Ge
(d) Se
Mendeleev predicted the existence of certain elements not known at that time and named two of them as eka-aluminium, and eka-silicon.
(a) Name the element which has taken the place of (i) eka-aluminium, and (ii) eka-silicon
(b) Mention the period/periods of these elements in the modern periodic table.
(c) Write the group/ groups of these elements in the modern periodic table.
(d) Classify these elements as metals, non-metals or metalloids.
(e) How many valence electrons are present in the atoms of each of these elements?
Match the columns.
| Column A | Column B |
| 1) Triads | a) Mendeleev |
| 2) Octave | b) Dobereiner |
| 3) Atomic number | c) Thomson |
| 4) Atomic mass number | d) Moseley |
| e) Newland |
Describe the merits of Mendeleev’s periodic table?
Match the column:
| Column ‘A’ | Column ‘B’ |
| Alkali metals | (a) Group 18 |
| Halogens | (b) Group 1 |
| Noble gases | (c) Group 17 |
