Overview
This lecture reviews key chemistry concepts essential for understanding microorganisms, focusing on atoms, ions, chemical bonds, pH, and properties of water.
Structure of Atoms
- Protons have a +1 charge, are in the nucleus, and define the element.
- Electrons have a -1 charge, negligible mass, orbit the nucleus, and their arrangement determines chemical reactivity.
- Valence electrons (outer shell) influence bonding and reactivity.
- Neutrons have no charge, are in the nucleus, and have a mass of one atomic unit.
Electronegativity
- Electronegativity is an atom's ability to attract electrons.
- It increases from left to right and decreases down the periodic table; fluorine is the most electronegative element.
Ions
- An uncharged atom has equal numbers of protons and electrons.
- Ions are atoms with unequal numbers of protons and electrons, carrying a net charge.
- Cations are positive ions formed when atoms lose electrons.
- Anions are negative ions formed when atoms gain electrons.
Chemical Bonds
- Covalent bonds involve sharing electrons and are strong, common in living organisms.
- Nonpolar covalent bonds share electrons equally (no difference in electronegativity).
- Polar covalent bonds share electrons unequally (higher electronegativity pulls electrons closer).
- Ionic bonds form from the attraction between cations and anions (e.g., sodium chloride).
- Hydrogen bonds are weak attractions between a slightly positive hydrogen and a negative atom (oxygen, nitrogen, fluorine) on another molecule.
Properties of Water
- Water is an excellent solvent (dissolves other substances).
- A solute is the substance that gets dissolved in a solvent.
- Hydrophilic molecules interact with and dissolve in water (form hydrogen bonds).
- Hydrophobic molecules do not dissolve in water (nonpolar; do not form hydrogen bonds).
pH and Acids/Bases
- pH measures hydrogen ion concentration, calculated as the negative log of [H+], and ranges from 0-14.
- Each pH unit change represents a tenfold change in [H+].
- Neutral substances have pH 7 (equal H+ and OH-).
- Acids have pH <7, donate H+ ions, and increase [H+].
- Bases (alkaline) have pH >7, reduce [H+], and increase OH-.
Key Terms & Definitions
- Proton — positively charged particle in atom nucleus.
- Electron — negatively charged particle orbiting the nucleus.
- Neutron — neutral particle in the nucleus.
- Valence Electrons — electrons in the outermost shell.
- Electronegativity — atom's ability to attract electrons.
- Cation — positively charged ion.
- Anion — negatively charged ion.
- Covalent Bond — bond formed by sharing electrons.
- Ionic Bond — bond formed by attraction between cation and anion.
- Hydrogen Bond — weak attraction between molecules involving hydrogen.
- Solvent — substance that dissolves another.
- Solute — substance being dissolved.
- Hydrophilic — water-loving, dissolves in water.
- Hydrophobic — water-fearing, does not dissolve in water.
- pH — measure of hydrogen ion concentration.
- Acid — substance that donates H+ (pH < 7).
- Base — substance that removes H+ (pH > 7).
Action Items / Next Steps
- Review related flashcards for reinforcement.
- Test your understanding with self-quizzing on key concepts and definitions.