Mendeleev left gaps in his periodic table and predicted the properties of eka-boron, eka-aluminium and eka-silicon. These elements were later discovered as:
- A.Sodium, potassium and calcium
- B.Cobalt, nickel and copper
- C.Scandium, gallium and germanium
- D.Radium, radon and rhenium
Correct answer
Explanation
The correct answer is C, Scandium, gallium and germanium. Mendeleev arranged the elements by increasing atomic mass in 1869 and left blank spaces where his pattern demanded an element that was not yet known. He described in advance the mass, density and compounds of three of them, calling them eka-boron, eka-aluminium and eka-silicon, and when scandium, gallium and germanium were discovered they matched his descriptions closely, which won the periodic law wide acceptance. Option A is wrong because sodium, potassium and calcium were all well known long before 1869. Option B is wrong because cobalt, nickel and copper were known too, and cobalt and nickel were in fact the pair he had to place out of strict mass order. Option D is wrong because radium, radon and rhenium were found much later and were not among his three predictions.
Read the full article: Atomic Structure and Periodic Table: Models and Trends
Practice Questions
View allWho coined the word 'atom'?
- A.Democritus
- B.Thomson
- C.E Rutherford
- D.John Dalton
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The Greek philosopher Democritus, working in the fifth century before the common era, argued that matter could be divided only up to a limit, and he called that smallest indivisible particle atomos, from which the word atom comes.
Read the full explanation →Who among the following discovered the neutrons?
- A.J. Chadwick
- B.E. Goldstein
- C.Neils Bohr
- D.Ernest Rutherford
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James Chadwick discovered the neutron in 1932 by bombarding beryllium with alpha particles and showing that the radiation produced consisted of neutral particles of nearly the same mass as the proton.
Read the full explanation →Rutherford's alpha-particle scattering experiment on a thin gold foil led to which conclusion?
- A.Electrons are embedded in a sphere of positive charge
- B.The atom is indivisible
- C.Electrons revolve in fixed permitted orbits
- D.Almost all the mass and the positive charge lie in a tiny nucleus
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Most alpha particles passed straight through the foil, a few were deflected through small angles and about one in twenty thousand bounced back.
Read the full explanation →The maximum number of electrons that can be accommodated in the M shell is:
- A.8
- B.2
- C.18
- D.32
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The capacity of a shell is given by the formula 2n squared, where n is the number of the shell counted outward from the nucleus.
Read the full explanation →Alkali metals are assigned which group in the Modern Periodic Table?
- A.Second group
- B.Eighteenth group
- C.Third group
- D.First group
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The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. Each has a single electron in its outermost shell, loses it readily to form a positive ion, and therefore stands in group 1 of the modern periodic table.
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