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Energy and IMFs Main Concept:
Potential energy is associated with the interaction of molecules; as molecules draw near each other, they experience an attractive force.
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IMF Review Hydrogen Bonding Energy and IMFs Chemical Process Physical Process Interactions in Biological Molecules
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Energy and IMFs IMF Review Hydrogen Bonding Energy and IMFs
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- Types of intermolecular forces:
- dipole-dipole: attractions b/w polar molecules - dipole-induced dipole: attractions b/w polar and nonpolar molecules - induced dipole-induced dipole (dispersion): attractions b/w nonpolar molecules
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- All substances will manifest dispersion forces, and these forces are larger when molecules involved have more electrons or have a larger surface area (size of atoms/molecules)
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- Hydrogen bonding relatively strong type of intermolecular interaction occurring b/w hydrogen atoms covalently bonded to highly electronegative atoms (N, O, and F) attracted to negative ends of a dipole formed by electronegative atoms (N, O, and F) in a different molecule or a different part of same molecule - When hydrogen bonding is present, even small molecules may have strong intermolecular attractions
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- When intermolecular forces are broken, that is an endothermic process
ie. ice melting due to heat - When intermolecular forces are formed, that is an exothermic process ie. ice forming due to removal of heat
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*known as solution formation
- When energy of separation is less than energy of formation (mixing), net reaction is exothermic - When energy of separation is greater than energy of formation (mixing), net reaction is endothermic endothermic process endothermic process exothermic process *known as solution formation
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Chemical vs Physical Processes
Main Concept: At the particulate scale, chemical processes can be distinguished from physical processes because chemical bonds can be distinguished from intermolecular interactions.
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Chemical vs Physical Processes
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- distinctions between chemical and physical processes relates to nature of change in molecular interactions - Processes that involve breaking and/or formation of chemical bonds = chemical processes - Processes involving only changes in weak intermolecular interactions, such as phase changes, are classified as physical processes
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- gray areas exists between these two extremes
Ex: dissolution of a salt in water involves breaking ionic bonds and formation of interactions between ions and solvent - magnitude of these interactions similar to covalent bond strengths, and so arguments can be made for classifying dissolution of salts as either a physical or chemical process.
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Biological Interactions
Main Concept: Noncovalent and intermolecular interactions play important roles in many biological and polymer systems.
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Biological Interactions
Interactions in Biological Molecules
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- In large biomolecules, noncovalent interactions may occur between different molecules or between different regions in same large biomolecule - functionality and properties of molecules depend strongly on shape of molecule, which is largely dictated by noncovalent interactions Ex: function of enzymes is dictated by structure, and properties of synthetic polymers are modified by manipulating chemical composition and structure
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