VSEPR Theory and Molecular Polarity Review

Vocabulary practice cards covering VSEPR rules, steric numbers, electron-pair and molecular geometries, bond angles, and molecular polarity principles.

Steric Number (SN)

The total value calculated as: (Number of atoms bonded to central atom) + (Number of lone pairs on central atom).

VSEPR Repulsion Strength Order

The hierarchy of electron pair repulsion: Lone Pair vs. Lone Pair > Lone Pair vs. Bonding Pair > Bonding Pair vs. Bonding Pair.

VSEPR Fundamental Principle

The concept that molecular geometry is primarily determined by electron-electron repulsive forces, driving valence shell electron pairs into maximum three-dimensional separation.

Bond Angle Compression Rule

The general principle where each nonbonding lone pair typically squeezes ideal molecular bond angles down by approximately $2^\circ$ to $2.5^\circ$.

Hydride Bond Angle Trend ($\text{H}_2\text{O} < \text{NH}_3 < \text{CH}_4$)

An increasing bond angle order caused by a decrease in the number of lone pairs on the central atom from $2$ to $1$ to $0$, which reduces repulsive compression on the bonding pairs.

Triiodide Ion ($\text{I}_3^-$)

An ion with a linear molecular geometry ($180^\circ$ bond angle) resulting from a central iodine atom with $2$ bonding domains and $3$ lone pairs (steric number $5$) positioned in equatorial slots.

Thiocyanate Ion ($\text{SCN}^-$)

A linear ion featuring carbon as the central atom with $2$ double bonds ($[\text{S}=\text{C}=\text{N}]^-$), $2$ electron domains, and $0$ lone pairs, producing a $180^\circ$ bond angle.

Ammonia ($\text{NH}_3$) Polarity and Angle

The most polar group hydride due to nitrogen's high electronegativity ($3.04$) and small size, featuring a trigonal pyramidal shape with an $H-N-H$ bond angle of approximately $107.3^\circ$ (less than $109.5^\circ$).

Chloromethane ($\text{CH}_3\text{Cl}$)

The chloromethane compound with the largest permanent net dipole moment, where three $\text{C}-\text{H}$ dipoles point inward and reinforce the polar $\text{C}-\text{Cl}$ bond dipole with minimal cancellation.

Sulfur Dioxide ($\text{SO}_2$)

A molecule that shares identical bent molecular geometry and $18$ valence electrons with the $\text{NO}_2^-$ ion, featuring a steric number of $3$ ($2$ bonding sites and $1$ lone pair).

Thionyl Tetrafluoride ($\text{SF}_4\text{O}$)

A molecule with trigonal bipyramidal molecular geometry where sulfur forms $4$ single bonds to $\text{F}$ and $1$ double bond to $\text{O}$ with $0$ central lone pairs (steric number $5$).

Phosphorus Trifluoride ($\text{PF}_3$) Steric Number

Steric number $4$, determined by $3$ single bonds to fluorine atoms and $1$ unshared lone pair on the central phosphorus atom.

Carbon Disulfide ($\text{CS}_2$)

A nonpolar molecule lacking a permanent net dipole moment because its symmetrical, linear $\text{S}=\text{C}=\text{S}$ geometry causes opposing $\text{C}=\text{S}$ dipoles to cancel cleanly.

Carbon Tetrafluoride ($\text{CF}_4$)

A symmetrical tetrahedral molecule with ideal $109.5^\circ$ bond angles and a net dipole moment of $0\text{ D}$ due to complete cancellation of its polar $\text{C}-\text{F}$ bond dipoles.

Chlorite Ion ($\text{ClO}_2^-$)

An ion with a bent molecular geometry and tetrahedral electron-pair framework, resulting from $2$ bonding domains and $2$ lone pairs on the central chlorine atom (steric number $4$).

Difluoromethane ($\text{CH}_2\text{F}_2$)

An asymmetric dihalogenomethane exhibiting the largest permanent net dipole moment among its series due to fluorine possessing the highest electronegativity.

Silicon Tetrafluoride ($\text{SiF}_4$) Geometry

A tetrahedral electron-pair and molecular geometry assigned to the central silicon atom based on $4$ bonding pairs and $0$ lone pairs (steric number $4$).

Seesaw Molecular Geometry

A molecular shape arising from steric number $5$ with $4$ bonding pairs and $1$ lone pair, exhibiting bond angles of $< 90^\circ$ and $< 120^\circ$ (e.g., $\text{SF}_4$).

T-Shaped Molecular Geometry

A molecular shape characterized by steric number $5$ with $3$ bonding pairs and $2$ lone pairs, exhibiting bond angles of $< 90^\circ$ and $180^\circ$ (e.g., $\text{ClF}_3$, $\text{ICl}_3$).

Square Pyramidal Molecular Geometry

A molecular shape derived from steric number $6$ with $5$ bonding pairs and $1$ lone pair, exhibiting bond angles of $< 90^\circ$ (e.g., $\text{BrF}_5$).

Square Planar Molecular Geometry

A molecular shape derived from steric number $6$ with $4$ bonding pairs and $2$ lone pairs, exhibiting bond angles of $90^\circ$ and $180^\circ$ (e.g., $\text{XeF}_4$).