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Question
Write the number of protons, neutrons and electronic configuration of \[\ce{_19^39K, _15^31P}\]. Also state their position in periodic table.
Solution
Atomic number = Number of protons
Hence, the number of protons in K atom = 19
Number of neutrons = Mass number − Atomic number
Hence, the number of neutrons in K atom = 39 − 19 = 20
Number of electrons = Number of protons
Hence, the number of electrons = 19
And electronic configuration of K atom = 2, 8, 8, 1
Since K atom has 4 shells, hence it belongs to fourth period.
With one valence electron, it belongs to group 1
Number of protons in P atom = 15
Number of neutrons in P atom = 31 − 15 = 16
Number of electrons in P atom = 15
And electronic configuration of P atom = 2, 8, 5
Since it has three shells, it belongs to period 3 and has 5 valence electrons. Phosphorus is found in five plus ten, which is the 15th group.
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