Overview
This lecture explains how chemical bonds form between atoms, distinguishes key types of bonds (ionic, covalent, hydrogen), and discusses their roles in physiology.
Molecules and Compounds
- Atoms form chemical bonds by interacting with valence electrons.
- A molecule consists of two or more atoms chemically bonded together.
- A compound is a molecule made of atoms from different elements (e.g., HโO).
Ions and Ionic Bonds
- An atom becomes an ion when it gains or loses electrons and acquires a charge.
- Cations are positively charged ions formed by losing electrons (e.g., Kโบ).
- Anions are negatively charged ions formed by gaining electrons (e.g., Fโป).
- Ionic bonds are the electrostatic attraction between oppositely charged ions (e.g., NaCl formation).
- Water breaks ionic bonds, allowing ions to move freely as electrolytes in biological fluids.
Covalent Bonds
- Covalent bonds form when atoms share electron pairs to fill their valence shells.
- Single, double, and triple covalent bonds share one, two, or three pairs of electrons, respectively.
- Nonpolar covalent bonds involve equal sharing of electrons, resulting in electrically balanced molecules.
- Polar covalent bonds have unequal sharing, causing regions with partial positive and negative charges (e.g., in HโO).
Polar Molecules and Dipoles
- A polar molecule has regions with opposite partial charges due to unequal electron sharing.
- The water molecule is polar: the oxygen end is slightly negative, hydrogen ends are slightly positive.
- Molecular polarity influences interactions with other molecules and ions.
Hydrogen Bonds
- Hydrogen bonds are weak attractions between a hydrogen atom (in a polar molecule) and an electronegative atom in another molecule.
- In water, hydrogen bonds form between slightly positive hydrogens and slightly negative oxygens of neighboring molecules.
- Hydrogen bonds explain water's ability to dissolve salts and its repulsion of nonpolar molecules like oils.
Key Terms & Definitions
- Molecule โ group of atoms held together by chemical bonds.
- Compound โ molecule with atoms from different elements.
- Ion โ atom with a positive or negative charge due to electron loss/gain.
- Cation โ positively charged ion.
- Anion โ negatively charged ion.
- Ionic Bond โ attraction between oppositely charged ions.
- Covalent Bond โ bond where atoms share electron pairs.
- Nonpolar Covalent Bond โ covalent bond with equal electron sharing.
- Polar Covalent Bond โ covalent bond with unequal electron sharing, creating partial charges.
- Hydrogen Bond โ weak attraction between a hydrogen atom in one molecule and an electronegative atom in another.
Action Items / Next Steps
- Review differences between ionic, covalent, and hydrogen bonds.
- Understand and define key terms listed above.
- Complete any assigned reading or practice on chemical bonding.