BIO 120 u1 p4

Basic Chemistry Overview

• Introduction to Chapter Two
  • Covers basic chemistry, water, organic chemistry, and macromolecules.
  • Four lectures planned for this chapter.
  • Interactive lecture style; encourages questions.
  • Lecture will be recorded for review.

Chemical Bonds

• Definition of chemical bonds

  • Interactions between atoms.
  • Form when electron shells are incomplete.
  • When atoms fill outer shells, they become more stable.
  • A complete energy shell results in a stable atom.

• Types of Chemical Bonds

  • Covalent Bonds
  • Ionic Bonds
  • Hydrogen Bonds

Valence Electrons

• Atoms and subatomic particles

  • Atoms: smallest units of matter.
  • Subatomic particles: protons, neutrons (in nucleus), electrons (surrounding nucleus).
  • Role of electrons in chemical behavior.

• Energy shells and electrons

  • Electrons occupy different energy shells.
  • Example: Carbon has two shells.
  • First shell: 2 electrons.
  • Second shell: 4 electrons (can hold 8).

• Valence Electrons

  • Outer electrons influencing chemical bonds.
  • Carbon has four valence electrons; thus, it is reactive.

Types of Chemical Bonds

• Covalent Bonds

  • Definition: Formed by sharing a pair of electrons between atoms.

  • Example: Hydrogen gas (H₂)

  • Each hydrogen has one electron.

  • Shares electron with another hydrogen to fill the first shell.

  • Stable configuration achieved through sharing.

  • Characteristics of Covalent Bonds

  • Types of Covalent Bonds:

    • Single Bond: sharing of one pair of electrons.
    • Double Bond: sharing of two pairs of electrons.
    • Triple Bond: sharing of three pairs of electrons.

  • Types of Polarities:

    • Polar Covalent Bonds:
    • Electrons are unevenly shared.
    • Results in partial positive and negative charges.
    • Example: Water (H₂O) is a polar molecule.
      • Oxygen is more electronegative than hydrogen, pulling shared electrons closer.
    • Nonpolar Covalent Bonds:
    • Electrons are evenly shared.
    • Example: Methane (CH₄) has equal sharing between carbon and hydrogen.

• Ionic Bonds

  • Definition: Formed between oppositely charged ions.
  • Example: Sodium (Na) and Chlorine (Cl)
  • Sodium donates one electron, becoming a positively charged ion (cation).
  • Chlorine accepts the electron, becoming a negatively charged ion (anion).
  • Forms Table Salt (NaCl).

• Hydrogen Bonds

  • Definition: Weak bonds formed between a hydrogen atom of one molecule and a highly electronegative atom (often oxygen) of another molecule.
  • Example: Water molecules (H₂O) exhibit hydrogen bonding.
  • Importance: Facilitate properties essential for life.

Properties of Water

• Earth’s unique water abundance

  • 71% of Earth is covered in water.
  • 60% of the human body is water.
  • Importance for all organisms and as a sign of potential life on other planets.

• Polarity of Water

  • Water is a polar molecule due to its covalent bonds.
  • Shape influenced by oxygen's electronegativity.

• Cohesion and Adhesion

  • Cohesion: Water’s ability to stick to itself due to hydrogen bonds.
  • Important for surface tension; some organisms can walk on water.
  • Adhesion: Water’s ability to stick to other surfaces (like xylem in plants).
  • Enables water transport in trees against gravity.

• Expansion Upon Freezing

  • Water expands when it freezes due to stable hydrogen bond configurations.
  • Ice is less dense than liquid water; ice floats.
  • Essential for aquatic life survival during winter.

• Temperature Moderation

  • Water can moderate temperature due to high specific heat capacity.
  • Important for maintaining stable temperatures in organisms and environments.

• Versatility as a Solvent

  • Water dissolves many substances due to its polarity.
  • Essential for biochemical reactions within organisms.

• Chemical Reactions

  • Involve breaking and forming of chemical bonds.
  • Reactants: substances entering the reaction.
  • Products: substances produced by the reaction.
  • Example: Formation of water from hydrogen and oxygen.

• Reversible Reactions

  • Chemical reactions can go both forward and backward to reach equilibrium.
  • Example: Water can split into hydrogen and oxygen, and vice versa.

• Metabolic Reactions

  • Overview of metabolic processes such as cellular respiration and photosynthesis.
  • Photosynthesis: converts CO₂ and water into glucose (C₆H₁₂O₆) and O₂.
  • Cellular Respiration: converts glucose and O₂ into ATP, water, and CO₂.
  • Photosynthesis and respiration are reversible processes.

Conclusion of Chapter Two

• Summary of key concepts: matter, atoms, elements of life, isotopes, electron behavior, chemical bonds, and equilibrium.
• Invitation for questions and further discussion.