Polar Covalent Bonds and Water in Biology - Quick Notes

Covalent, Ionic, and Hydrogen Bonds

• Covalent bonds: atoms share electrons; positive charges attract negative charges; like charges repel.
• Ionic bonds: electrons transferred; full charges created.
• Hydrogen bonds: weaker, non-covalent interactions based on partial charges; crucial for biology.

Polar Covalent Bonds and Electronegativity

• Polar covalent bonds: uneven electron sharing.
• Partial charges: $\delta^-$ on the more electronegative atom; $\delta^+$ on the less electronegative atom.
• Electronegativity differences drive polarity; emphasis on relative pull in biology.

Key Elements for Electronegativity in Biology

• Six elements: Oxygen, nitrogen, sulfur, carbon, hydrogen, and phosphorus.
• Oxygen and nitrogen are the most electronegative among these in this context and pull electrons more in covalent bonds.

Water, Polarity, and Hydrogen Bonding

• Water molecules are polar; hydrogen bonding arises from partial charges.
• Within a water molecule, covalent bonds hold H and O together; partial negative on O and partial positive on H.
• Hydrogen bonds between water molecules are crucial for biology.

Biological Implications: Cell Membranes and Ice

• Polar covalent bonds and hydrogen bonding support life; membranes are built from hydrophobic components that are excluded from water.
• Water exclusion around membranes helps form compartments; life can persist under ice in cold environments.
• Ice is less dense than liquid water, so it floats; this allows life to exist under frozen surfaces.