The modern periodic law states that the properties of elements are a periodic function of their:
- A.Atomic mass
- B.Atomic number
- C.Density
- D.Valency
Correct answer
Explanation
The correct answer is B, atomic number. Henry Moseley showed in 1913, from the frequencies of the X-rays that elements emit, that the atomic number, the number of protons in the nucleus, is the more fundamental property of an element. The periodic law was therefore restated: the properties of elements are a periodic function of their atomic numbers. Option A is wrong because atomic mass was the basis of Mendeleev's law of 1869, which could not place isotopes and needed pairs such as cobalt and nickel to be put out of mass order. Option C is wrong because density is a physical property that shows no simple periodic pattern of this kind. Option D is wrong because valency follows from the electron arrangement and so is itself a consequence of the atomic number, not the basis of the law.
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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