Question

1. choose the group that does not contain isotopes of the same element.

(a)
(b)
(c)
(d)
use the diagram below to answer question 20.
the letter ( n ) in ( n s^{2} n p^{1} ) represents an integer, where ( n=1,2,3 ). etc. the families in the periodic table
are labeled letters ( q - y ) in the periodic table above.

1. the electron configuration of the valence electrons of an atom in its ground state is ( n s^{2} n p^{1} ).

this atom is a group _ element.
(a) ( q )
(b) ( r )
(c) ( s )
(d) ( t )

Explanation:

Question 19

Step1: Recall the definition of isotopes

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

Step2: Analyze each option

• Option (A):
• Atom I: Protons \(=18\), Neutrons \(=18\)
• Atom II: Protons \(=18\), Neutrons \(=19\)
• Since protons are same (\(Z = 18\)), these are isotopes of argon (\(Ar\)).
• Option (B):
• Atom I: Protons \(=25\), Neutrons \(=30\)
• Atom II: Protons \(=25\), Neutrons \(=31\)
• Since protons are same (\(Z = 25\)), these are isotopes of manganese (\(Mn\)).
• Option (C):
• Atom I: Protons \(=37\), Neutrons \(=42\)
• Atom II: Protons \(=37\), Neutrons \(=41\)
• Since protons are same (\(Z = 37\)), these are isotopes of rubidium (\(Rb\)).
• Option (D):
• Atom I: Protons \(=82\), Neutrons \(=126\)
• Atom II: Protons \(=81\), Neutrons \(=126\)
• Since protons are different (\(Z_1=82\) and \(Z_2 = 81\)), these are not isotopes.

Step1: Determine the number of valence electrons

The electron configuration of valence electrons is \(ns^{2}np^{1}\). The number of valence electrons \(=2 + 1=3\).

Step2: Relate to periodic - table groups

• Group 1 (alkali metals): \(ns^{1}\)
• Group 2 (alkaline - earth metals): \(ns^{2}\)
• Group 13: \(ns^{2}np^{1}\)

Answer:

D. Atom I: 82 protons, 126 neutrons; Atom II: 81 protons, 126 neutrons

Question 20