- Draw the Lewis formula for a) BrF3; b) NH2- ; and c) SiC14 2. What terms describe the shapes of the species mentioned in number 1? a) BrF3; b) NH2- ; and c) SiC14 3. Predict the geometry of the following species: a) SCO | b) BeCl2 c) PC15 4. Give the hybridization of the central atom in each of the following species? a) SiC14 b) NH2CI c) ONCI 5. How may electron domains are there in the following molecule? a. H2 b. NH3 c. XeF22- d. SF4 e. ICI4- None
the correct answer and explanation is:
1. Lewis Structures
a) BrF₃:
Bromine (Br) is the central atom with three single bonds to fluorine atoms and two lone pairs.
b) NH₂⁻:
Nitrogen (N) is the central atom, bonded to two hydrogen atoms with one lone pair and an extra electron (giving it a negative charge).
c) SiCl₄:
Silicon (Si) is the central atom, with four single bonds to chlorine atoms and no lone pairs.
2. Molecular Shapes
a) BrF₃: T-shaped.
The presence of two lone pairs on bromine causes a T-shaped molecular geometry.
b) NH₂⁻: Bent.
The lone pair on nitrogen creates a bent geometry.
c) SiCl₄: Tetrahedral.
With no lone pairs on silicon, the geometry is tetrahedral.
3. Predicted Geometry
a) SCO: Linear.
SCO has a triple bond between C and O and a single bond between S and C, forming a linear shape.
b) BeCl₂: Linear.
Beryllium chloride has no lone pairs on Be, leading to a linear geometry.
c) PCl₅: Trigonal bipyramidal.
Phosphorus is surrounded by five bonding pairs, forming a trigonal bipyramidal shape.
4. Hybridization of the Central Atom
a) SiCl₄: sp³.
Silicon forms four sigma bonds, requiring sp³ hybridization.
b) NH₂Cl: sp³.
Nitrogen is bonded to two hydrogens and one chlorine, with one lone pair, resulting in sp³ hybridization.
c) ONCl: sp².
Oxygen forms a double bond with nitrogen and a single bond with chlorine, requiring sp² hybridization.
5. Electron Domains
a) H₂: 1 electron domain (single bond).
b) NH₃: 4 electron domains (3 bonds, 1 lone pair).
c) XeF₂²⁻: 5 electron domains (2 bonds, 3 lone pairs).
d) SF₄: 5 electron domains (4 bonds, 1 lone pair).
e) ICl₄⁻: 6 electron domains (4 bonds, 2 lone pairs).
Explanation
The Lewis structures of molecules are based on valence electrons around the central atom. Bromine in BrF₃ uses five valence electrons to bond with three fluorine atoms, leaving two lone pairs. The T-shaped geometry results from electron-pair repulsion. NH₂⁻ has nitrogen with two bonding pairs and a lone pair, forming a bent shape. SiCl₄ has silicon bonded to four chlorine atoms in a tetrahedral shape due to even electron distribution.
For predicting geometries, we apply the VSEPR theory. SCO is linear because of sp hybridization in carbon. BeCl₂ is linear as Be uses sp hybrid orbitals to minimize repulsion. PCl₅ adopts a trigonal bipyramidal shape, consistent with five bonding pairs around phosphorus.
Hybridization explains orbital mixing for sigma bonding. Si in SiCl₄ uses sp³ orbitals for its tetrahedral geometry. Nitrogen in NH₂Cl uses sp³ orbitals due to one lone pair. In ONCl, oxygen uses sp² orbitals as it participates in a double bond.
Electron domains count lone pairs and bonding regions. H₂ has a single bonding domain. NH₃ includes three bonding domains and one lone pair. XeF₂²⁻ has five domains, including lone pairs on xenon. SF₄ has five domains with one lone pair, and ICl₄⁻ has six domains, with two lone pairs.
These principles demonstrate how molecular shape, hybridization, and electron domains are interrelated.