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QuestionChemistry

BCl^3 is a non-polar molecule, but why does it form polar bonds?
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Step 1:
I'll solve this problem step by step, explaining the molecular structure and bonding of BCl^3.

Step 2:
: Understand the Molecular Structure

- BCl^3 is a trigonal planar molecule with boron (B) at the center - Boron has 3 valence electrons, and chlorine has 7 valence electrons - Each B-Cl bond is formed by sharing electrons

Step 3:
: Analyze the Electronegativity Difference

- Electronegativity difference: $$3.16 - 2.04 = 1.12
- Boron (B) electronegativity: 2.04 - Chlorine (Cl) electronegativity: 3.16 - This significant difference creates polar covalent bonds

Step 4:
: Explain Polar Bonds

- And a partial positive charge ($$\delta^{+}$$) on boron
- The electronegativity difference causes unequal electron sharing - Chlorine pulls electron density more strongly toward itself

Step 5:
: Understand Molecular Polarity

- Despite polar B-Cl bonds, the trigonal planar geometry - Symmetrical arrangement of three identical Cl atoms - Dipole moments cancel out, resulting in a non-polar molecule

Final Answer

BCl^3 forms polar bonds due to the significant electronegativity difference between boron and chlorine, but its symmetrical molecular geometry results in a non-polar molecule overall.