Question

part a
which molecule is polar?
sf₂
cs₂
pcl₅
bf₃

Explanation:

• For \(SF_2\):
• The central atom \(S\) has \(6\) valence electrons. It forms \(2\) single bonds with \(F\) atoms (\(2\) bonding pairs) and has \(2\) lone pairs (\(6 - 2= 4\) non - bonding electrons, \(4\div2 = 2\) lone pairs).
• According to VSEPR theory, the electron - pair geometry is tetrahedral and the molecular geometry is bent.
• The \(S - F\) bonds are polar (due to the difference in electronegativity: \(S: 2.58\), \(F: 3.98\)). Since the molecule is bent, the bond dipoles do not cancel out, making \(SF_2\) a polar molecule.
• For \(CS_2\):
• The central atom \(C\) has \(4\) valence electrons. It forms \(2\) double bonds with \(S\) atoms (\(2\) bonding pairs, no lone pairs as \(4-4 = 0\)).
• According to VSEPR theory, the electron - pair geometry and molecular geometry are linear.
• The \(C - S\) bonds are polar ( \(C: 2.55\), \(S: 2.58\)), but due to the linear symmetry of the molecule (\(\text{O}=\text{C}=\text{O}\) - like structure), the bond dipoles cancel each other out, making \(CS_2\) a non - polar molecule.
• For \(PCl_5\):
• The central atom \(P\) has \(5\) valence electrons. It forms \(5\) single bonds with \(Cl\) atoms (\(5\) bonding pairs, no lone pairs as \(5 - 5=0\)).
• According to VSEPR theory, the electron - pair geometry and molecular geometry are trigonal bipyramidal.
• The \(P - Cl\) bonds are polar (\(P: 2.19\), \(Cl: 3.16\)). But due to the symmetry of the trigonal bipyramidal structure, the bond dipoles cancel each other out (the axial \(P - Cl\) bond dipoles cancel each other and the equatorial \(P - Cl\) bond dipoles cancel each other), making \(PCl_5\) a non - polar molecule.
• For \(BF_3\):
• The central atom \(B\) has \(3\) valence electrons. It forms \(3\) single bonds with \(F\) atoms (\(3\) bonding pairs, no lone pairs as \(3-3 = 0\)).
• According to VSEPR theory, the electron - pair geometry and molecular geometry are trigonal planar.
• The \(B - F\) bonds are polar (\(B: 2.04\), \(F: 3.98\)). But due to the symmetry of the trigonal planar structure, the bond dipoles cancel each other out, making \(BF_3\) a non - polar molecule.

Answer:

\(SF_2\)