Chemistry and Ecosystem Ecology

Chemistry & Ecosystem Ecology Fundamentals

Introduction to Energy in Ecosystems

• Last Unit Focus: Energy movement through ecosystems, conversion between kinetic energy (light, heat, movement) and potential energy (chemical).

• Current Unit Focus: Examination of how energy is stored in chemicals and how these chemicals are cycled through an ecosystem.

Biogeochemical Cycles

• Definition: The cyclic movements of major inorganic components through ecosystems.

• Key Cycles Addressed (Global):

  • Water Cycle: $H_2O$

  • Nitrogen Cycle: $N<em>2$, $NO</em>x$, $NH_3$

  • Carbon Cycle: Organic molecules, $CO_2$

Atomic Structure and Bonding

Components of an Atom

• Protons: Positively charged particles, located in the nucleus.

• Neutrons: Neutrally charged particles, located in the nucleus.

• Electrons: Negatively charged particles, orbit the nucleus.

• Atomic Number: Equals the number of protons.

• Mass Number (Atomic Weight): Equals the total number of protons and neutrons.

Electrons and Orbitals

• Location: Electrons are found in orbitals around the nucleus.

• Orbital Capacity: Each orbital can hold a maximum of $2$ electrons.

• Electron Shells: Orbitals are grouped into shells.

  • First Shell: Maximum of $2$ electrons.

  • Additional Shells: Maximum of $8$ electrons each.

• Filling Rule: Once a shell is full, additional electrons move to the next shell.

• Valence Electrons: Electrons in the outermost shell.

  • Preference: Valence electrons prefer to be in full shells.

  • Options for Unfilled Shells (Stability):

    1. Share Electrons: Forms covalent bonds.

    2. Gain or Lose an Electron: Forms ions.

Types of Chemical Bonds

• Covalent Bonds: Electrons are shared between two atoms.

  • Examples: Hydrogen ($H<em>2$), Oxygen ($O</em>2$), Water ($H<em>2O$), Methane ($CH</em>4$).

  • Polar vs. Nonpolar Covalent Bonds:

    • Nonpolar Covalent Bond: Electrons are shared equally between atoms (e.g., $H_2$). Atoms have no partial charges.

    • Polar Covalent Bond: Electrons are shared unequally, leading to partial charges on the atoms (e.g., $H_2O$ with $ext{O}$ having a partial negative charge ($ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ 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  • Identifying Polarity: A bond is polar if atoms have partial charges.

    • Polar Cues: Linear molecules like $ext{CO}$; molecules with a single $ext{H}$ like $ext{HCl}$; molecules with an $ext{OH}$ at one end like $C<em>2H</em>5OH$; molecules with an $ext{O}$ or $ext{N}$ at one end like $ext{CH}<em>2 ext{O}$ or $ext{NH}</em>3$. Does it look like water ($ext{H-O-H}$)?

    • Nonpolar Cues: Diatomic molecules of the same element (e.g., $O_2$).

• Ionic Bonding: Electrons are transferred from one atom to another.

  • Result: Formation of positively charged ions ($+$, cations) and negatively charged ions ($-$, anions).

  • Bond Type: The attraction between these oppositely charged ions forms an ionic bond (e.g., $Na^+Cl^-$).

• Electron-Sharing Continuum: Shows the spectrum from nonpolar covalent (equal sharing, no charge) to polar covalent (unequal sharing, partial charges) to ionic (transfer of electrons, full charges).

Properties of Water

Water ($H_2O$) is an essential molecule for life with many unique properties due to its polar nature (oxygen has a $ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } ext{ } 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• Cohesion: Water molecules have a high affinity for other water molecules due to hydrogen bonding.

  • Biological Consequence: Allows water to be transported up tall trees against gravity (transpiration pull).

• Surface Tension: A measure of how difficult it is to stretch or break the surface of a liquid; high in water due to strong cohesive forces.

  • Biological Consequence: Enables some insects to walk on water.

• Density: Water is unusual because its solid form (ice) is less dense than its liquid form.

  • Maximum Density: Liquid water is densest at $4^ ext{o} ext{C}$.

  • Biological Consequence: Ice floats on liquid water, insulating aquatic ecosystems and allowing life to persist underneath during winter.

• Solvent Properties: Water is known as the