In long form of periodic table an element 'E' has atomic number 78. The period and group number of the element are x and y respectively. (x+y) is equal to
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To quickly find the period of an element with atomic number Z, locate it between the atomic numbers of the noble gases (2, 10, 18, 36, 54, 86, 118). The period number corresponds to the row of the next noble gas. For the group, identify the block (s, p, d) and apply the corresponding rule.
Step 1: Identify the element and its electron configuration.
The element with atomic number Z=78 is Platinum (Pt).
To find its period and group, we can write its electron configuration or use its position relative to the noble gases.
The noble gas preceding Pt is Xenon (Xe, Z=54). The next noble gas is Radon (Rn, Z=86).
Since Z=78 is between 54 and 86, the element is in the period of Radon, which is the 6th period. So, \(x=6\).
The full electron configuration for Pt is [Xe] \(4f^{14} 5d^9 6s^1\). (Note: This is an exception to the Aufbau principle; the expected is \(5d^8 6s^2\)).
Step 2: Determine the group number.
Platinum is a d-block element. For d-block elements (Groups 3-12), the group number is the sum of the electrons in the outermost s-shell and the penultimate d-shell.
Group Number = (number of ns electrons) + (number of (n-1)d electrons).
Using the actual configuration: Group = 1 (from 6s) + 9 (from 5d) = 10.
Using the expected (Aufbau) configuration: Group = 2 (from 6s) + 8 (from 5d) = 10.
In either case, the group number is 10. So, \(y=10\).
Step 3: Calculate the required sum.
We need to find the value of (x+y).
\( x+y = 6 + 10 = 16 \).
