Chapter 2 Part 1: Chemistry Foundations for Biology

Why a Biology Course Talks About Chemistry

• Biology and chemistry are inseparable: every biological function is driven by chemical interactions inside and between cells.

• The course will focus on the chemical principles most relevant to life (no heavy stoichiometry or mol-mass calculations).

• Goal: understand bonding and the roles of key biomolecules rather than mastering full-blown general chemistry.

Matter & Its Four States

• Definition of matter: anything that

  • Has mass (measure of the amount of “stuff,” independent of gravity).

  • Occupies space (possesses volume).

• Classical states

  • Solid → add energy → Liquid → add more energy → Gas.

• Modern addition

  • Plasma (energy state beyond gas; molecules/atoms so energized they ionize and behave collectively).

  • Examples: stars, flames (NOT the plasma in TVs or blood).

• For most bio-chemistry we care about solids, liquids, gases; plasma is conceptually useful but rarely part of cell biology discussions.

Elements: The Raw Materials of Matter

• 118 total elements on the periodic table; 92 occur naturally.

• In biology, we mostly worry about ~6 core elements (C, H, O, N, P, S) plus a few supporting players (e.g., Na, K, Ca, Cl, Mg, Fe).

• Elements are unique and cannot be chemically broken into simpler substances.

Atoms – Substructure & Charges

• Three sub-atomic particles

  • Protons: positive charge, reside in nucleus, contribute to atomic mass.

  • Neutrons: neutral, nucleus, contribute to mass.

  • Electrons: negative, extremely small mass, occupy orbitals (electron cloud) surrounding nucleus.

• Mass vs. weight

  • Atomic "mass" is used because weight requires gravity; chemists work with mass.

Electron Shells, Orbitals & the Octet Rule

• Electrons occupy discrete energy levels (“shells” or “rings”).

• Shell capacity (for the biologically relevant elements):

  • 1st shell: $2\,e^-$ max.

  • 2nd shell: $8\,e^-$ max.

  • 3rd shell (in the range we use): $8\,e^-$ max (rule of eights / octet rule).

• Valence shell = outermost occupied shell; chemistry is dominated by filling/emptying this shell.

• Goal of most atoms: reach a stable configuration (often an octet) either by

  • Losing electrons,

  • Gaining electrons,

  • Sharing electrons (covalent bonds).

Navigating the Periodic Table

• Rows (periods) tell you the number of occupied shells/orbital rings.

  • Row 1 → 1 shell; Row 2 → 2 shells; Row 3 → 3 shells, etc.

• Columns (groups) identify how many electrons are in the valence shell (exception: the H/He column).

  • Column 1 (alkali metals + H): 1 valence $e^-$.

  • Column 2 (alkaline earth metals): 2 valence $e^-$, etc.

• Noble gases (Group 18) have full valence shells ⇒ chemically inert.

• A periodic table was provided in course materials (downloadable PDF).

Atomic-Box Anatomy (Example: Calcium)

• Every element’s box lists

  • Atomic symbol (e.g., Ca).

  • Atomic number: # of protons.

  • Atomic mass: weighted average of all naturally occurring isotopes (protons + neutrons).

  • Element name.

• Electrically neutral rule:
  \text{# electrons}=\text{# protons}
  (Ions deviate from this by losing/gaining electrons).

Isotopes & Radioactivity

• Isotopes: atoms of the same element with different neutron counts.

• Example – Carbon

  • $^{12}\text{C}$ ≈ 97 % of natural carbon.

  • $^{13}\text{C}$ ≈ 2.97 %.

  • $^{14}\text{C}$ ≈ 0.03 %; radioactive, used in radiometric dating (decays over time).

• Atomic mass on the table is the weighted average of isotopic masses (hence decimals).

Key Biologically Important Elements – What the Periodic Table Tells Us

• Hydrogen (H)

  • Atomic # 1 → 1 proton, 1 electron.

  • Single valence $e^-$ ⇒ highly reactive; forms polar bonds with O and N.

• Helium (He)

  • Only 2 protons/electrons, fills 1st shell ⇒ inert (prototype noble gas).

• Carbon (C)

  • Atomic # 6 → 2 electrons in 1st shell, 4 in 2nd (valence).

  • 4 open spots ⇒ can form up to 4 covalent bonds (tetrahedral geometry).

  • Basis of organic chemistry; backbone of biomolecules.

• Nitrogen (N)

  • 5 valence $e^-$ ⇒ tends to form 3 covalent bonds (as in amino groups).

• Oxygen (O)

  • 6 valence $e^-$ ⇒ forms 2 strong bonds; highly electronegative.

  • Drives water’s polarity; crucial for cellular respiration.

• Phosphorus (P) & Sulfur (S)

  • Key for ATP, nucleic acids (P) and disulfide bridges in proteins (S).

• Sodium (Na), Potassium (K), Calcium (Ca), Chlorine (Cl)

  • Important ions for nerve impulses, muscle contraction, osmotic balance.

Noble Gases – The Non-Participants

• Group 18 elements (He, Ne, Ar, Kr, Xe, Rn, Og) have 8 electrons in valence (or 2 for He).

• Do not readily form chemical bonds; function mostly as inert gases.

Examples & Visualizing Electron Shells

• Drawing oxygen (O)

  1. Nucleus: 8 protons, (≈)8 neutrons.

  2. First shell: 2 electrons.

  3. Second shell: 6 electrons (needs 2 more to fill ⇒ motivates bonding).

• Water molecule illustration shorthand: $H_2O$ (2 H atoms share electrons with 1 O atom to complete valence shells).

• Practice exercise (suggested by lecturer): sketch atoms for P, Cl, Na, etc., by subtracting protons from rounded atomic mass to estimate neutron count and placing electrons according to row/column rules.

Real-World & Cross-Disciplinary Connections

• Carbon’s 4-bond flexibility ⇒ speculation about silicon-based life (Si is in the same group and also has 4 valence $e^-$).

• Carbon-14 dating links nuclear physics, geology, and paleontology to biology.

• Metals like Hg (mercury) are liquid at room temp; Au (gold), Ag (silver), W (tungsten) highlight diversity of elemental properties.

• Radioactive elements (U, Pu) tie into energy production and weaponry; mostly beyond bio scope but show periodic breadth.

Ethical / Philosophical Notes

• Understanding isotopes and radioactivity is essential for responsible use in medicine (e.g., PET scans) and environmental monitoring.

• Comprehending element stability underscores why certain gases can accumulate without reacting (e.g., noble gases in the atmosphere).

Practical Study Tips

• Keep a periodic table handy; focus on rows 1–3 plus biologically essential elements.

• Memorize element symbols for C, H, O, N, P, S, Na, K, Ca, Cl, Mg, Fe.

• Practice drawing electron shells to visualize bonding potential.

• Remember:
  $\text{Column} \Rightarrow \text{valence electrons}$
  $\text{Row} \Rightarrow \text{number of shells}$

• For quick neutron estimate:
  $\text{Neutrons} \approx \text{rounded mass} - \text{protons}$
  (sufficient for introductory biology).

End of Chapter 2 chemistry foundations. The next lecture will build from this atomic/elementary knowledge into actual biomolecules and their functions.