Overview
This lecture covers how to read chemical formulas and equations, highlights key chemical element symbols to recognize, and explains the basic rules for understanding chemical notation in biology.
Important Chemical Elements & Symbols
- You only need to recognize the most common elements, not memorize the whole periodic table.
- C = Carbon (core of organic molecules/chemistry)
- H = Hydrogen
- O = Oxygen
- N = Nitrogen
- P = Phosphorus
- S = Sulfur (occasional, esp. in proteins)
- Na = Sodium (not S because S is sulfur)
- Mg = Magnesium
- K = Potassium (not P because P is phosphorus)
- Ions are especially important for cell membranes and ionic bonds.
Reading Chemical Formulas
- Chemical symbols start with a capital letter; second letter (if any) is lower case.
- Subscript numbers apply only to the element before them (e.g., H₂O = 2 hydrogens, 1 oxygen).
- No subscript means “1” (e.g., CH₄ = 1 carbon, 4 hydrogens).
- A coefficient in front (e.g., 6 H₂O) applies to the whole molecule: multiply each subscript by the coefficient.
- Example: 6 H₂O means 12 hydrogens (6×2) and 6 oxygens (6×1) in separate water molecules, not one molecule.
Reading Chemical Equations
- Example: Cellular respiration: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O.
- Arrow points from reactants (left) to products (right).
- Atoms are neither created nor destroyed (Law of Conservation of Matter).
- The number and type of each atom on both sides must be equal.
- Coefficients multiply all atoms in a molecule; subscripts refer only to the atom they follow.
- Compounds can form through covalent (sharing electrons) or ionic (attraction of charged ions) bonds.
Covalent vs. Ionic Bonds
- Covalent bond: atoms share electrons (e.g., H₂).
- Ionic bond: positive and negative ions attract (e.g., Na⁺Cl⁻).
- Ionic compounds’ charges are balanced in the compound.
Hydrogen Bonds (Preview/Review)
- Water molecules are weakly attracted through hydrogen bonds, shown with dotted lines.
Key Terms & Definitions
- Subscript — small number after an element symbol showing how many atoms of that element are in the molecule.
- Coefficient — big number in front of a formula indicating the number of molecules.
- Reactant — starting substances in a chemical reaction.
- Product — substances formed by a chemical reaction.
- Law of Conservation of Matter — matter is not created or destroyed in chemical reactions.
- Covalent bond — chemical bond formed by sharing electrons.
- Ionic bond — bond formed between oppositely charged ions.
- Hydrogen bond — weak attraction between hydrogen and another electronegative atom (e.g., oxygen).
Action Items / Next Steps
- Memorize the key element symbols (C, H, O, N, P, S, Na, Mg, K).
- Practice reading and interpreting chemical formulas and equations.
- Watch the hydrogen bond lecture if not already completed.