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Exploring the Nature of Hydrogen Bonds
Sep 4, 2024
Lecture Notes: Understanding Hydrogen Bonds
Introduction
Hydrogen bonds are an attractive force between certain molecules.
Weaker than ionic or covalent bonds because they require less energy to break.
A large number of hydrogen bonds can exert a strong force.
Characteristics of Hydrogen Bonds
Result from an unequal charge distribution on a molecule; such molecules are called polar.
Form between hydrogen atoms covalently bonded to oxygen, nitrogen, or fluorine.
Example: Water Molecule
Structure:
Water (Hâ‚‚O) consists of one oxygen and two hydrogen atoms.
10 protons in total: 8 from oxygen, 1 each from the hydrogen atoms.
10 electrons in total:
2 shared between the oxygen and each hydrogen atom.
6 non-shared electrons from the oxygen atom.
Polarity:
Electrically neutral overall but has a partial positive (hydrogen side) and a partial negative (oxygen side).
Electrons are not equally shared; more likely found near the oxygen nucleus, giving it a negative charge.
The hydrogen end of the molecule has a slightly positive charge.
Hydrogen Bonding in Water:
Positive end of one water molecule is weakly attached to the negative end of an adjacent molecule.
Few hydrogen bonds in liquid form, many in solid form, none in gaseous form due to molecule distance.
Importance of Hydrogen Bonds
Crucial in the structure of proteins and nucleic acids (topics for future discussions).
Polar vs. Non-Polar Molecules
Polar molecules (e.g., water) have slightly positive and negative ends.
Non-polar molecules (e.g., lipids, fats, oils) share electrons equally in bonds.
Non-polar molecules do not form hydrogen bonds with polar molecules (e.g., water and oil do not mix due to polarity differences).
Conclusion
Water molecules are polar, enabling formation of hydrogen bonds.
Hydrogen bonds play a key role in the physical properties of substances and biological structures.
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