The question asks about the basis of Henry Moseley's Modern Periodic Law. We need to identify the experimental evidence and the key discovery that led to the establishment of atomic number as the fundamental property for arranging elements.
A) X-ray spectra of elements — he found that the square root of the frequency of characteristic X-rays was directly proportional to the atomic number Z, establishing atomic number as the more fundamental property. This accurately describes Moseley's experimental work and its profound implication for the Modern Periodic Law.
The question asks about the Modern Periodic Law. This law is a fundamental principle in chemistry that describes the arrangement of elements in the periodic table and the periodicity of their properties. We need to recall the precise statement of the Modern Periodic Law to identify the correct option.
Correct Option: B) The physical and chemical properties of elements are a periodic function of their ATOMIC NUMBERS
The question asks about the structure of the modern periodic table, specifically the number of periods and groups. Understanding the organization of elements in the periodic table is fundamental to chemistry.
Correct Option: C) 7 periods (horizontal rows) and 18 groups (vertical columns)
The question asks for the number of elements in each period of the modern periodic table. This can be determined by understanding the electron shell filling rules and the maximum number of electrons each shell can accommodate.
Thus, the number of elements in periods 1, 2, 3, 4, 5, 6, and 7 are 2, 8, 8, 18, 18, 32, and 32 respectively.
D) 2, 8, 8, 18, 18, 32, 32
The number of elements in a period of the periodic table is determined by the number of orbitals available for electron filling in that principal energy level, following the Aufbau principle and Hund's rule. We need to identify which orbitals are being filled in the 6th period.
B) The 6th period involves filling of 6s (2e), 4f (14e), 5d (10e) and 6p (6e) orbitals: total 2+14+10+6 = 32 electrons (and hence 32 elements). This option correctly identifies all the orbitals being filled in the 6th period and their respective electron capacities, leading to a total of 32 elements.
The question asks for the definition of a 'PERIOD' in the modern periodic table. We need to recall the organization of elements in the periodic table, specifically the meaning of horizontal rows and vertical columns.
C) A horizontal row in the periodic table; all elements in a period have the same number of electron shells (same value of principal quantum number n for the outermost shell). This statement accurately defines a period in the modern periodic table. Each period corresponds to the filling of a new electron shell, meaning all elements within that period have the same number of occupied electron shells.