Chapter 1 ~B - Chemistry Past Paper PDF
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Summary
This document covers various aspects of chemistry, including molecular polarity, dipole moments, and the intermolecular forces. It delves into concepts like induction, resonance, and how these affect properties like boiling point. The document discusses the relationship between molecular structure and physical characteristics.
Full Transcript
1.12 Molecular Polarity & Dipoles Induction ⇒dipole moment Dipole moment =↑ EN differencex↑ atom radius Note:C-heteroatom leads to a dipole Why does a large radius result in a greater dipole moment? ↑ radius = ↑ distance over which charge separation occurs (...
1.12 Molecular Polarity & Dipoles Induction ⇒dipole moment Dipole moment =↑ EN differencex↑ atom radius Note:C-heteroatom leads to a dipole Why does a large radius result in a greater dipole moment? ↑ radius = ↑ distance over which charge separation occurs (moving two magnets apart you feel that force getting stronger) - This is why C-X (halides) have ↑ EN difference, due to the large size of X How can we get dipoles? 1. Induction 2. Resonance Net Dipole Moment - Note:LP causes the arrow to point towards it becauseit’s e dense Note: You need to draw dashes and wedges, not theLewis structure What if molecules have multiple polar bonds? 1.13 Intermolecular Forces Neutral (not charged) molecules are attracted to one another through: Dipole-dipole interactions H-bonding LDF or “fleeting dipole-dipole forces” Dipole - Dipole Occur whenpolarmolecules line up theiroppositecharges ↑ polar = ↑ dipole-dipole force = ↑ BP & ↑MP H-bonding → Occurs b/w H and the lone-pair of NO Strong type of dipole-dipole force ○ Strong b/c H is very small, so all that 𝛿+ is concentratedand is large + ⇒ large 𝛿+ attracts other 𝛿- ⇒ stronger electrostatic forces ⇒ stronger H-bonds Protic vs Aprotic Solvents Protic~ Solvents that engage in H-bonding (form H-bondswith itself) Aprotic ~Solvents thatcan’tengage in H-bonding(don’t form H-bonds with itself) London Dispersion If 2 molecules are non-polar ⇒ induced, transient dipole ⇒ LDF Weak, but if it accumulates it’s strong ↑ SA (bigger atom) = ↑ mass = ↑ temporary dipole attractions = ↑ BP What causes a decrease in BP? ↑ branching = ↓ BP This is b/c branching ↓SA and LDF need ↑SA to make transient dipoles
