Hybridization — Revision Notes

⚡ 30-Second Revision

Definition: — Mixing of atomic orbitals to form new hybrid orbitals.
Purpose: — Explains molecular geometry and equivalent bonds.
Steric Number (SN): — $ext{SN} = (\text{sigma bonds}) + (\text{lone pairs})$
Hybridization Types & Geometry:

- SN=2: $sp$, Linear, $180^circ$ - SN=3: $sp^2$, Trigonal Planar, $120^circ$ - SN=4: $sp^3$, Tetrahedral, $109.5^circ$ - SN=5: $sp^3d$, Trigonal Bipyramidal, $90^circ, 120^circ$ - SN=6: $sp^3d^2$, Octahedral, $90^circ$ - SN=7: $sp^3d^3$, Pentagonal Bipyramidal, $72^circ, 90^circ$

Lone Pair Effect: — LP-LP > LP-BP > BP-BP repulsion, reduces bond angles.
s-character: — Higher s-character $implies$ more electronegative, shorter/stronger bond.

2-Minute Revision

Hybridization is a theoretical concept where an atom's atomic orbitals (s, p, d) mix to form a new set of equivalent hybrid orbitals. This process is crucial for explaining the observed molecular shapes and the equivalence of bonds, which simple orbital overlap cannot fully account for.

The type of hybridization is determined by the steric number (SN), which is the sum of sigma bonds and lone pairs around the central atom. For example, SN=4 means $sp^3$ hybridization (tetrahedral electron geometry), SN=3 means $sp^2$ (trigonal planar), and SN=2 means $sp$ (linear).

Elements in Period 3 and beyond can involve d-orbitals, leading to $sp^3d$ (SN=5) and $sp^3d^2$ (SN=6) hybridizations. It's vital to remember that lone pairs occupy hybrid orbitals and exert greater repulsion than bonding pairs, leading to deviations from ideal bond angles (e.

g., $CH_4 > NH_3 > H_2O$ bond angles). Hybrid orbitals form sigma bonds, while unhybridized p-orbitals form pi bonds. The s-character of a hybrid orbital influences its electronegativity and bond properties.

5-Minute Revision

Hybridization is a fundamental concept in chemical bonding that describes the mixing of atomic orbitals of similar energy on the same atom to form a new set of degenerate (equal energy) hybrid orbitals.

This theoretical model helps explain the specific molecular geometries and the equivalence of bonds observed in molecules, which are not predicted by the simple overlap of pure atomic orbitals. For instance, carbon in methane ($CH_4$) undergoes $sp^3$ hybridization to form four equivalent bonds in a tetrahedral arrangement.

The most practical way to determine hybridization for NEET is the steric number (SN) method. SN is calculated as the sum of the number of sigma bonds formed by the central atom and the number of lone pairs on that central atom. Pi bonds are not counted in the steric number. The SN directly correlates with the hybridization type:

SN = 2 $implies$ $sp$ (linear geometry, $180^circ$)
SN = 3 $implies$ $sp^2$ (trigonal planar geometry, $120^circ$)
SN = 4 $implies$ $sp^3$ (tetrahedral electron geometry, $109.5^circ$)
SN = 5 $implies$ $sp^3d$ (trigonal bipyramidal electron geometry)
SN = 6 $implies$ $sp^3d^2$ (octahedral electron geometry)

Example: $NH_3$

1
Central atom: N (5 valence electrons).
2
Sigma bonds: 3 (with 3 H atoms).
3
Lone pairs: $(5 - 3)/2 = 1$.
4
SN = $3 + 1 = 4$. $implies$ $sp^3$ hybridization. Electron geometry is tetrahedral, but molecular geometry is trigonal pyramidal due to the lone pair.

Impact of Lone Pairs: Lone pairs occupy more space and exert greater repulsion than bonding pairs (LP-LP > LP-BP > BP-BP). This repulsion compresses bond angles from their ideal values. For example, $CH_4$ ($sp^3$, 0 LP) has $109.5^circ$, $NH_3$ ($sp^3$, 1 LP) has $approx 107^circ$, and $H_2O$ ($sp^3$, 2 LP) has $approx 104.5^circ$.

s-character: The percentage of s-orbital character in a hybrid orbital affects its properties. Higher s-character (e.g., $sp$ with 50%) leads to greater electronegativity, shorter bond lengths, and stronger bonds compared to $sp^2$ (33.3%) or $sp^3$ (25%). This is crucial for understanding the acidity of C-H bonds in organic compounds.

For NEET, practice identifying hybridization in various inorganic and organic molecules, including those with expanded octets (e.g., $PCl_5, SF_6, XeF_4$) and multiple bonds.

Prelims Revision Notes

Hybridization: Quick Recall for NEET

1. Definition & Purpose:

Mixing of atomic orbitals (s, p, d) of similar energy on the same atom.
Forms new, equivalent, directional hybrid orbitals.
Explains observed molecular geometries and equivalent bond strengths/angles.
Not a real physical process, but a theoretical model.

2. Steric Number (SN) Method:

SN = (Number of sigma bonds) + (Number of lone pairs)
Steps:

1. Identify central atom. 2. Count its valence electrons (adjust for charge in ions). 3. Count sigma bonds (1 for single, 1 for double, 1 for triple). 4. Calculate lone pairs: (Valence electrons - electrons used in sigma bonds) / 2. 5. Sum sigma bonds and lone pairs for SN.

3. Hybridization Types & Geometries:

SN	Hybridization	Electron Geometry	Molecular Geometry (0 LP)	Bond Angle (Ideal)
2	$sp$	Linear	Linear	$180^circ$
3	$sp^2$	Trigonal Planar	Trigonal Planar	$120^circ$
4	$sp^3$	Tetrahedral	Tetrahedral	$109.5^circ$
5	$sp^3d$	Trigonal Bipyramidal	Trigonal Bipyramidal	$90^circ, 120^circ$
6	$sp^3d^2$	Octahedral	Octahedral	$90^circ$
7	$sp^3d^3$	Pentagonal Bipyramidal	Pentagonal Bipyramidal	$72^circ, 90^circ$

4. Lone Pair Effects (VSEPR Connection):

Lone pairs (LP) occupy more space than bonding pairs (BP).
Repulsion order: LP-LP > LP-BP > BP-BP.
Lone pairs distort ideal bond angles (e.g., $CH_4 (109.5^circ) > NH_3 (107^circ) > H_2O (104.5^circ)$, all $sp^3$).

5. s-character and Properties:

$sp$: 50% s-character (most electronegative, shortest/strongest bonds)
$sp^2$: 33.3% s-character
$sp^3$: 25% s-character (least electronegative, longest/weakest bonds)
Higher s-character $implies$ greater electronegativity, shorter bond length, stronger bond, more acidic C-H bond.

6. Organic Chemistry Specifics:

Carbon atoms: $sp^3$ (all single bonds), $sp^2$ (one double bond), $sp$ (one triple bond or two double bonds).
Always count only sigma bonds for SN of carbon (assume no lone pairs).

7. Common Examples to Remember:

$sp$: $BeCl_2, C_2H_2, CO_2$
$sp^2$: $BF_3, C_2H_4, SO_2$
$sp^3$: $CH_4, NH_3, H_2O, CCl_4$
$sp^3d$: $PCl_5, SF_4, ClF_3, I_3^-$
$sp^3d^2$: $SF_6, XeF_4, BrF_5$
$sp^3d^3$: $IF_7$

**8. Pi ($pi$) Bonds:** Formed by sideways overlap of *unhybridized* p-orbitals. Do not count towards steric number.

Vyyuha Quick Recall

To remember the hybridization types and their steric numbers:

Six People Danced Together On Platforms.

Steric Number 2: SP
Steric Number 3: SP2
Steric Number 4: SP3
Steric Number 5: SP3D
Steric Number 6: SP3D2 (Two D's for Octahedral)
Steric Number 7: SP3D3 (Outstanding D's for Pentagonal Bipyramidal)

This mnemonic helps link the steric number to the type of hybridization by associating the number with the count of orbitals involved (s=1, p=1-3, d=1-3).