Molecular Lewis Dot Structure Formula Number of Electrons – Molecular Geometry Domains HCN (1(4)(5)) = C≡N Linear SO3 (3(6)(3)) = S=O Trigonal Planar SiH4 (4(4)(0)) = SiH4 Tetrahedral PF5 (5(1)(0)) = PCl5 Trigonal Bipyramidal SF6 (6(0)(0)) = SF6 Octahedral
The Correct Answer and Explanation is:
To help you understand the molecular structures and the corresponding electron domains, let’s break down each molecule step by step:
1. HCN (Hydrogen Cyanide)
- Lewis Dot Structure: The carbon (C) atom forms a triple bond with nitrogen (N), and the carbon atom is also bonded to one hydrogen (H) atom.
- Formula: H-C≡N
- Number of Electrons: Total valence electrons = 1 (H) + 4 (C) + 5 (N) = 10 electrons
- Molecular Geometry: The geometry is linear, which arises because the central carbon atom has a triple bond with nitrogen and a single bond with hydrogen. The molecule adopts this structure to minimize electron repulsion, which is a characteristic of a linear shape.
2. SO3 (Sulfur Trioxide)
- Lewis Dot Structure: Sulfur (S) forms double bonds with each of the three oxygen (O) atoms.
- Formula: O=S=O
- Number of Electrons: Total valence electrons = 6 (O) × 3 + 6 (S) = 24 electrons
- Molecular Geometry: The molecular geometry is trigonal planar, where the sulfur atom is at the center and the oxygen atoms are placed symmetrically around it in a plane. This occurs due to the arrangement of the electron pairs around sulfur, which allows for the maximum spatial separation, creating a trigonal planar shape.
3. SiH4 (Silane)
- Lewis Dot Structure: Silicon (Si) is bonded to four hydrogen (H) atoms via single bonds.
- Formula: SiH4
- Number of Electrons: Total valence electrons = 4 (Si) + 1 (H) × 4 = 8 electrons
- Molecular Geometry: The geometry is tetrahedral because the silicon atom is surrounded by four hydrogen atoms in a symmetrical arrangement, with 109.5° bond angles, characteristic of a tetrahedral shape.
4. PF5 (Phosphorus Pentafluoride)
- Lewis Dot Structure: Phosphorus (P) is bonded to five fluorine (F) atoms via single bonds.
- Formula: PF5
- Number of Electrons: Total valence electrons = 5 (P) + 7 (F) × 5 = 40 electrons
- Molecular Geometry: The geometry is trigonal bipyramidal. Phosphorus forms five bonds with fluorine, and the arrangement of these bonds around phosphorus leads to the characteristic trigonal bipyramidal shape with 90° and 120° bond angles.
5. PCl5 (Phosphorus Pentachloride)
- Lewis Dot Structure: Phosphorus (P) is bonded to five chlorine (Cl) atoms via single bonds.
- Formula: PCl5
- Number of Electrons: Total valence electrons = 5 (P) + 7 (Cl) × 5 = 40 electrons
- Molecular Geometry: Similar to PF5, PCl5 also adopts a trigonal bipyramidal shape, as the phosphorus atom is surrounded by five chlorine atoms with electron pairs arranged in a way to minimize repulsion.
6. SF6 (Sulfur Hexafluoride)
- Lewis Dot Structure: Sulfur (S) is bonded to six fluorine (F) atoms via single bonds.
- Formula: SF6
- Number of Electrons: Total valence electrons = 6 (S) + 7 (F) × 6 = 48 electrons
- Molecular Geometry: The molecular geometry is octahedral because the sulfur atom is surrounded symmetrically by six fluorine atoms. The bond angles between the fluorines are 90° and 180°, giving the molecule an octahedral shape.
Key Points:
- Electron domains refer to regions where electrons are most likely to be found. These can be bonding pairs or lone pairs.
- The geometry of a molecule is determined by the number of bonding and lone pairs of electrons around the central atom, and how these electron domains arrange themselves to minimize repulsion.
- The molecular geometry dictates the shape of the molecule, which in turn influences its physical and chemical properties.
This explanation provides the correct molecular geometries based on the number of electron domains and valence electrons in each molecule.
