Draw the Lewis structure and state the VSEPR for each of the following: a) BH3 b) OCl2 c) SnCl2 d) SF4
The correct answer and explanation is:
Here are the Lewis structures and VSEPR shapes for each molecule:
a) BH3 (Borane)
- Lewis structure: Boron (B) is the central atom with three hydrogen atoms bonded to it. Boron has 3 valence electrons and each hydrogen has 1 valence electron. All electrons are involved in single bonds, no lone pairs on boron.
- VSEPR shape: BH3 has 3 bonding pairs and 0 lone pairs on the central atom. According to VSEPR theory, the shape is Trigonal Planar with bond angles of approximately 120 degrees.
b) OCl2 (Dichlorine monoxide)
- Lewis structure: Oxygen is the central atom with two chlorine atoms bonded to it. Oxygen has 6 valence electrons, each chlorine has 7. Oxygen forms two single bonds with chlorine atoms and has two lone pairs of electrons on it.
- VSEPR shape: Oxygen has 2 bonding pairs and 2 lone pairs. This gives the molecule a Bent (Angular) shape. The bond angle is slightly less than 109.5 degrees due to lone pair repulsion.
c) SnCl2 (Tin(II) chloride)
- Lewis structure: Tin (Sn) is the central atom with two chlorine atoms bonded to it. Tin has 4 valence electrons, each chlorine has 7. Tin forms two single bonds with chlorines and has one lone pair on the central atom.
- VSEPR shape: SnCl2 has 2 bonding pairs and 1 lone pair. This corresponds to a Bent shape with bond angles less than 120 degrees.
d) SF4 (Sulfur tetrafluoride)
- Lewis structure: Sulfur is the central atom with four fluorine atoms bonded to it. Sulfur has 6 valence electrons, fluorine has 7 each. Sulfur forms four single bonds with fluorines and has one lone pair.
- VSEPR shape: SF4 has 4 bonding pairs and 1 lone pair on sulfur. This arrangement produces a Seesaw shape due to lone pair repulsion in a trigonal bipyramidal electron geometry.
Explanation (300 words)
The Lewis structure of a molecule shows the arrangement of valence electrons around atoms, including bonds and lone pairs. This helps predict molecular shape using Valence Shell Electron Pair Repulsion (VSEPR) theory. VSEPR states that electron pairs around a central atom repel each other and will arrange to minimize repulsion.
In BH3, boron has three bonding pairs and no lone pairs. These pairs repel equally, arranging in a trigonal planar shape with 120-degree bond angles. This results in a flat triangular shape.
In OCl2, oxygen bonds to two chlorines and has two lone pairs. Lone pairs repel more strongly than bonding pairs, pushing the bonded atoms closer. This causes a bent shape with bond angles less than the tetrahedral angle of 109.5 degrees.
For SnCl2, tin bonds to two chlorines and holds one lone pair. With three regions of electron density, the electron geometry is trigonal planar, but the presence of the lone pair distorts the molecule into a bent shape, reducing the bond angle to less than 120 degrees.
In SF4, sulfur bonds to four fluorines and has one lone pair, creating five electron regions around sulfur. The electron geometry is trigonal bipyramidal. The lone pair occupies an equatorial position to minimize repulsion, causing the bonded atoms to arrange in a seesaw shape.
Understanding Lewis structures and VSEPR shapes helps predict molecular polarity, reactivity, and physical properties, crucial in chemistry and materials science.