HC VSEPR & Polarity Check-In

According to VSEPR, molecules adjust their shapes to keep which of the following as far away as possible?

• Pairs of valence electrons

• Inner shell electrons

• Mobile Electrons

• Electrons closest to the nucleus

Answer explanation

According to VSEPR theory, molecules adopt shapes that minimize repulsion between electron pairs. Therefore, they adjust to keep pairs of valence electrons as far apart as possible, which is crucial for determining molecular geometry.

What geometry is this? (The balloon-like shapes are lone pairs!)

• Linear

• Trigonal Pyramidal

• Bent

• Tetrahedral

Answer explanation

The geometry is bent because the lone pairs (balloon-like shapes) repel the bonding pairs, causing the molecule to adopt a bent shape rather than a linear or tetrahedral arrangement.

What is the geometry of this molecule?

• Tetrahedral

• Linear

• Trigonal Pyramidal

• Trigonal Planar

Answer explanation

The molecule has a tetrahedral geometry, which occurs when a central atom is bonded to four other atoms with no lone pairs, resulting in bond angles of approximately 109.5 degrees.

Which molecule would have this shape (linear)?

• BF₃

• CH₄

• PCl₃

• CO₂

Answer explanation

CO2 has a linear shape due to its two double bonds and no lone pairs on the central carbon atom, resulting in a bond angle of 180 degrees. In contrast, BF3, CH4, and PCl3 have different geometries.

What molecule could this be? (Look at how many domains it has!)

• BF₃

• CH₄

• H₂O

• CO₂

Answer explanation

BF3 has three bonding domains around the boron atom, indicating it is a trigonal planar molecule. In contrast, CH4, H2O, and CO2 have different numbers of domains, making BF3 the correct choice.

SiCl₄ has what shape?

• Trigonal pyramid

• bent

• tetrahedral

• Trigonal planar

Answer explanation

SiCl4 has a tetrahedral shape due to its four bonding pairs of electrons around the central silicon atom, which repel each other equally, resulting in a three-dimensional arrangement.

What Shape would BH₃ form?

• Trigonal Pyrimidal

• Trigonal Planar

• Tetrahedral

• Bent

Answer explanation

BH3 has three hydrogen atoms bonded to a central boron atom with no lone pairs, resulting in a trigonal planar shape. The bond angles are approximately 120 degrees, confirming the trigonal planar geometry.

What shape would PH₃ have?

• Trigonal Planar

• Trigonal pyramidal

• Bent

• Linear

Answer explanation

PH3 has a central phosphorus atom bonded to three hydrogen atoms and one lone pair of electrons. This arrangement leads to a trigonal pyramidal shape due to the repulsion between the lone pair and the bonding pairs.

Consider the molecule below.  Determine the molecular geometry at each of the 2 labeled carbons.

• C1 = tetrahedral, C2 = linear

• C1 = trigonal planar, C2 = bent

• C1 = bent, C2 = trigonal planar

• C1 = trigonal planar, C2 = tetrahedral

Answer explanation

C1 has three bonds and no lone pairs, resulting in a trigonal planar geometry. C2 has four bonds and no lone pairs, leading to a tetrahedral geometry. Thus, the correct answer is C1 = trigonal planar, C2 = tetrahedral.

Tags

NGSS.HS-PS1-3

What shape does CH₂Br₂ have?

• Tetrahedral

• Trigonal Planar

• Bent 

• Trigonal Pyramidal

Answer explanation

C2H2Br2 has a central carbon atom bonded to two bromine atoms and two hydrogen atoms. This arrangement leads to a tetrahedral shape due to the four regions of electron density around the carbon, confirming the correct answer is Tetrahedral.