Atomic Structure

Step 1: Understanding the Concept:
Bond order indicates bond strength. Higher bond order means shorter bond length and higher bond enthalpy.

Step 2: Detailed Explanation:
(A) Correct: Bond order = (Nb - Na)/2.
(B) Correct: Isoelectronic species have same electronic configuration, hence same bond order.
(C) Incorrect: Bond enthalpy increases with bond order.
(D) Correct: Bond length decreases as bond order increases.
(E) Correct: Bond enthalpy increases with bond order.

Step 3: Final Answer:
The incorrect statement is that bond enthalpy decreases with increase in bond order.

Step 1: Understanding the Concept:
The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas.

Step 2: Detailed Explanation:
Check the central atom in each compound:
• BF : Boron has only 6 electrons in its valence shell (incomplete octet).
• BeH : Beryllium has only 4 electrons (incomplete octet).
• SCl : Sulfur has 6 valence electrons. It forms two single bonds with two Chlorine atoms, using 2 electrons. The remaining 4 electrons exist as two lone pairs. Total electrons around S = 4 (from bonds) + 4 (from lone pairs) = 8. Complete octet.
• AlCl : Aluminum has 6 electrons in its valence shell.
• LiCl: This is an ionic compound, not a covalent molecule with a central atom in the traditional sense.

Step 3: Final Answer:
SCl is the compound where the central atom (S) has a complete octet.

Step 1: Understanding the Concept:
The d-subshell consists of five orbitals, which are mathematically derived from the Schrödinger wave equation. These orbitals describe the regions in space where there is a high probability of finding an electron. Their three-dimensional shapes are distinctive.
Step 2: Key Formula or Approach:
The theoretical approach involves visualizing or recalling the boundary surface diagrams (shapes) of the five standard d-orbitals: , (written as here), (or ), , and .
Step 3: Detailed Explanation:
Let's describe the shapes of the given orbitals:
- A) , B) , C) : These three are non-axial orbitals. Each consists of a characteristic "cloverleaf" shape made up of four lobes of electron density that lie in the planes between the coordinate axes (xy plane, xz plane, and yz plane, respectively).
- D) : This is an axial orbital. It also possesses a "cloverleaf" shape with four lobes. However, unlike the first three, its lobes are aligned directly along the x and y coordinate axes.
- E) : This orbital is fundamentally different in appearance. It is a linear combination of two mathematical solutions. Its shape consists of two major lobes oriented along the z-axis (resembling a p-orbital) and a concentric torus (a donut-shaped ring) of electron density situated in the xy-plane around the nucleus. Therefore, it does not have four lobes.
Step 4: Final Answer:
The orbital is unique among the d-orbitals as it does not possess a four-lobed structure.

Step 1: Understanding the Concept:
Iso-electronic species are atoms or ions that have the same number of electrons. To identify them, we look at the atomic number of the neutral atom and adjust for the charge (subtract for positive charge, add for negative charge).
Step 2: Detailed Explanation:
1. Na⁺ (11-1=10) and Mg²⁺ (12-2=10): Both have 10 electrons. (Iso-electronic)
2. Mn²⁺ (25-2=23) and Fe³⁺ (26-3=23): Both have 23 electrons. (Iso-electronic)
3. Fe²⁺ (26-2=24) and Mn²⁺ (25-2=23): These have different numbers of electrons.
4. O²⁻ (8+2=10) and F⁻ (9+1=10): Both have 10 electrons. (Iso-electronic)
Step 3: Final Answer:
The pair Fe²⁺ and Mn²⁺ is not iso-electronic.

Step 1: Understanding the Question:
The question asks for the bond order of the nitrosonium ion ( ). This can be determined using Molecular Orbital (MO) Theory.

Step 2: Key Formula or Approach:
Bond Order = (Bonding electrons - Antibonding electrons).
First, calculate the total number of valence electrons:
Electrons from = 7
Electrons from = 8
Subtract 1 electron due to the positive charge ( ).
Total electrons = electrons.

Step 3: Detailed Explanation:
Since has 14 electrons, it is isoelectronic with the Nitrogen molecule ( ) and Carbon Monoxide ( ).
The Molecular Orbital (MO) electronic configuration for a 14-electron species is:

Counting the electrons:
Number of bonding electrons ( ) = 2 (from ) + 2 (from ) + 4 (from ) + 2 (from ) = 10
Number of antibonding electrons ( ) = 2 (from ) + 2 (from ) = 4
Using the formula:
Bond Order = .
A bond order of 3 indicates a triple bond between Nitrogen and Oxygen.

Step 4: Final Answer:
The bond order is 3.