21) The electron configuration 1s2 2s2 2p6 3s2 3p6 fits all of the following species except one. The exception is ________.
A) F−
B) Ca2+
C) S2−
D) P3−
22) What behavior is expected from an atom with the electron configuration 1s2 2s2 2p6 3s2 3p6 4s2?
A) gain of 2 electrons
B) loss of 2 electrons
C) gain of 6 electrons
D) loss of 4 electrons
23) Which ion is isoelectronic with Kr?
A) Cl−
B) O2−
C) Rb+
D) Ba2+
24) Which of the following is not isoelectronic with a noble gas?
A) Li+
B) Ba2+
C) S−
D) F−
25) Which one of the following sets contains species that are all isoelectronic?
A) O, F, Ne
B) C+4, N-3, O-2
C) P-3, S-2, Ar
D) Na, Mg, Al
26) Which of the following ions is not isoelectronic with the noble gas neon?
A) O-2
B) F-
C) Al+3
D) S-2
27) Which of the following compounds contains an ion with a 3+ charge?
A) KCl
B) AlP
C) BeF2
D) BaO
28) Which of the following compounds contains an ion with a 2− charge?
A) AlP
B) MgS
C) KBr
D) BaCl2
29) In the formation of the ionic compound CaBr2, the number of electrons transferred from one Ca atom to two Br atoms, per formula unit, is ________.
A) 1
B) 2
C) 3
D) 4
30) In the process of forming sodium nitride, Na3N, each sodium atom ________ electron(s) and each nitride atom ________ electron(s).
A) loses one; gains two
B) loses three; gains one
C) loses three; gains three
D) loses one; gains three
The Correct Answer and Explanation is :
Let’s analyze each question to determine the correct answers and understand the reasoning behind them.
21) The electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ fits all of the following species except one. The exception is:
This electron configuration corresponds to 18 electrons, which is the configuration of Argon (Ar). Let’s examine each species:
- A) F⁻: Fluorine (atomic number 9) gains one electron to become F⁻, resulting in 10 electrons.
- B) Ca²⁺: Calcium (atomic number 20) loses two electrons to form Ca²⁺, resulting in 18 electrons.
- C) S²⁻: Sulfur (atomic number 16) gains two electrons to form S²⁻, resulting in 18 electrons.
- D) P³⁻: Phosphorus (atomic number 15) gains three electrons to form P³⁻, resulting in 18 electrons.
Therefore, the exception is A) F⁻, as it has only 10 electrons, not 18.
22) What behavior is expected from an atom with the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²?
This configuration corresponds to Calcium (Ca), which has two electrons in the 4s orbital. To achieve a stable noble gas configuration (like Argon), calcium tends to lose these two 4s electrons.
- B) loss of 2 electrons is the correct behavior.
23) Which ion is isoelectronic with Kr?
Krypton (Kr) has 36 electrons. Let’s evaluate each ion:
- A) Cl⁻: Chlorine (atomic number 17) gains one electron to have 18 electrons.
- B) O²⁻: Oxygen (atomic number 8) gains two electrons to have 10 electrons.
- C) Rb⁺: Rubidium (atomic number 37) loses one electron to have 36 electrons.
- D) Ba²⁺: Barium (atomic number 56) loses two electrons to have 54 electrons.
Therefore, C) Rb⁺ is isoelectronic with Kr, as both have 36 electrons.
24) Which of the following is not isoelectronic with a noble gas?
Isoelectronic species have the same number of electrons as a noble gas.
- A) Li⁺: Lithium (atomic number 3) loses one electron to have 2 electrons, like Helium.
- B) Ba²⁺: Barium (atomic number 56) loses two electrons to have 54 electrons, like Xenon.
- C) S⁻: Sulfur (atomic number 16) gains one electron to have 17 electrons, which does not match any noble gas.
- D) F⁻: Fluorine (atomic number 9) gains one electron to have 10 electrons, like Neon.
Therefore, C) S⁻ is not isoelectronic with a noble gas.
25) Which one of the following sets contains species that are all isoelectronic?
Isoelectronic species have the same number of electrons.
- A) O, F, Ne: Oxygen (8 electrons), Fluorine (9 electrons), Neon (10 electrons).
- B) C⁴⁺, N³⁻, O²⁻: Carbon ion (2 electrons), Nitrogen ion (10 electrons), Oxygen ion (10 electrons).
- C) P³⁻, S²⁻, Ar: Phosphorus ion (18 electrons), Sulfur ion (18 electrons), Argon (18 electrons).
- D) Na, Mg, Al: Sodium (11 electrons), Magnesium (12 electrons), Aluminum (13 electrons).
Therefore, C) P³⁻, S²⁻, Ar are all isoelectronic with 18 electrons each.
26) Which of the following ions is not isoelectronic with the noble gas neon?
Neon has 10 electrons.
- A) O²⁻: Oxygen ion with 10 electrons.
- B) F⁻: Fluorine ion with 10 electrons.
- C) Al³⁺: Aluminum ion with 10 electrons.
- D) S²⁻: Sulfur ion with 18 electrons.
Therefore, D) S²⁻ is not isoelectronic with neon.
27) Which of the following compounds contains an ion with a 3+ charge?
- A) KCl: Contains K⁺ and Cl⁻.
- B) AlP: Contains Al³⁺ and P³⁻.
- C) BeF₂: Contains Be²⁺ and F⁻.
- D) BaO: Contains Ba²⁺ and O²⁻.
Therefore, B) AlP contains Al³⁺, an ion with a 3+ charge.
28) Which of the following compounds contains an ion with a 2− charge?
- A) AlP: Contains P³⁻.
- B) MgS: