Overview
This lecture covers covalent, ionic, and hydrogen bonds, explaining electronegativity, polar and non-polar covalent bonds, hydrogen bonding, and their significance in biological molecules.
Covalent Bonds and Electronegativity
- Covalent bonds involve the sharing of electron pairs between atoms.
- Atoms with equal electronegativity, like two carbons, share electrons equally (non-polar covalent bond).
- Electronegativity is the attraction an atom has for electrons.
- When atoms like oxygen and hydrogen share electrons, the sharing is unequal due to their different electronegativities (polar covalent bond).
- Oxygen and nitrogen are highly electronegative and often attract electrons more strongly in bonds.
Polar vs. Non-polar Covalent Bonds
- Non-polar covalent bonds involve equal sharing of electrons, resulting in no charge separation.
- Polar covalent bonds involve unequal electron sharing, causing partial negative and positive charges on the participating atoms.
- In a water molecule, oxygen has a partial negative charge, and hydrogens have partial positive charges due to unequal sharing.
Ionic Bonds
- Ionic bonds form when electrons are transferred between atoms, creating full positive and negative charges.
- Atoms with 1, 2, 3, or 7 electrons in their outer shell tend to form ionic bonds.
Rules of Thumb for Bond Formation
- Atoms with 1-3 or 7 valence electrons usually transfer electrons (ionic bonds).
- Atoms with 4, 5, or 6 valence electrons typically share electrons (covalent bonds).
Hydrogen Bonds
- Hydrogen bonds form between molecules, not within a molecule, as a weak attraction between a partially positive hydrogen and a partially negative atom (often oxygen or nitrogen).
- Hydrogen bonds are responsible for interactions between water molecules and shape large molecules like DNA and proteins.
- Hydrogen bonds are weak individually but are significant when many are present.
Bond Strength Ranking
- Covalent bonds are the strongest, followed by ionic bonds, with hydrogen bonds being the weakest.
Key Terms & Definitions
- Electronegativity — an atom's tendency to attract electrons in a bond.
- Non-polar covalent bond — equal sharing of electrons between atoms.
- Polar covalent bond — unequal sharing of electrons, resulting in partial charges.
- Ionic bond — transfer of electrons creating fully charged ions.
- Hydrogen bond — weak attraction between a partially positive hydrogen and a partially negative atom in different molecules.
- Valence electrons — electrons in the outermost shell of an atom.
Action Items / Next Steps
- Practice definitions and bond types using questions in the "Testing Your Understanding" section on Canvas.
- Complete the lecture exam one practice questions on chemical reactions and bonds.
- Review the upcoming slides about hydrogen bonding and water’s special properties.