S1.3 Electron Configuration

Which condensed electron configuration is correct for the Al³⁺ ion?

• [Ne]3s²3p¹
• [Ne]
• [Ne]3s²
• [He]2s²2p⁶

Answer explanation

Al atom: [Ne]3s²3p¹. Removing 3 electrons gives Al³⁺ = [Ne].

What is the full electron configuration of the nitride ion, N³⁻?

• 1s² 2s² 2p³
• 1s² 2s² 2p⁵
• 1s² 2s² 2p⁶
• 1s² 2s² 2p⁴

Answer explanation

N atom: 1s² 2s² 2p³. Adding 3 electrons → 1s² 2s² 2p⁶.

Which element has the condensed electron configuration [Ar]4s²3d¹⁰4p²?

• Ge (Z=32)
• Si (Z=14)
• Se (Z=34)
• Br (Z=35)

Answer explanation

[Ar]4s²3d¹⁰4p² corresponds to Ge, group 14, period 4.

The copper atom (Z = 29) has an unusual ground-state electron configuration. Which is correct?

• [Ar]4s²3d⁷
• [Ar]4s²3d⁹
• [Ar]4s¹3d¹⁰
• [Ar]3d¹⁰

Answer explanation

Cu exception: [Ar]4s¹3d¹⁰ is more stable than [Ar]4s²3d⁹.

Which of the following represents the ground-state electron configuration of the Zn²⁺ ion?

• [Ar]3d¹⁰
• [Ar]3d⁸
• [Ar]3d¹⁰4s²
• [Ar]3d¹⁰4p²

Answer explanation

Zn atom: [Ar]4s²3d¹⁰. Loss of 2 electrons → Zn²⁺ = [Ar]3d¹⁰.

An element has the electron configuration [Kr]5s²4d¹⁰5p⁵. To which group and period does this element belong?

• Group 17, Period 5
• Group 16, Period 5
• Group 15, Period 4
• Group 17, Period 4

Answer explanation

[Kr]5s²4d¹⁰5p⁵ is iodine, group 17 (halogen), period 5.

Which electron configuration corresponds to the ground state of Mn²⁺ (Z = 25)?

• [Ar]3d⁵
• [Ar]3d³4s²
• [Ar]3d⁷
• [Ar]4s²3d⁵

Answer explanation

Mn atom: [Ar]4s²3d⁵. Loss of 2 electrons → Mn²⁺ = [Ar]3d⁵.

What is the maximum number of electrons that can occupy the third energy level (n = 3)?

• 8
• 10
• 18
• 32

Answer explanation

n=3 → 3s, 3p, 3d orbitals → 2 + 6 + 10 = 18 electrons.

Which of the following ions has the same electron configuration as argon?

• Ca²⁺
• K⁺
• Cl⁻
• All of the above

Answer explanation

Ca²⁺ (20-2=18e⁻), K⁺ (19-1=18e⁻), Cl⁻ (17+1=18e⁻) → all = Ar.

Which of the following is the correct electron configuration for the ground state of vanadium, V (Z = 23)?

• [Ar]4s²3d³
• [Ar]4s¹3d⁴
• [Ar]3d⁵
• [Ne]3s²3p⁶3d⁵

Answer explanation

Vanadium follows the normal pattern: [Ar]4s²3d³.