Water: The Basis of Marine Ecology PART 1/3

🌊 Water: The Basis of Marine Ecology

💧 Water (H2O)

Water is the foundation of marine ecology. Our planet is approximately 75% water, leading some to suggest that it should have been named "Ocean" instead of "Earth".

🧊 Changes in State of Water

The changes in the state of water (solid, liquid, and gas) can be explained through the kinetic particle theory.

• Temperature: Measure of the motion of particles.

• Solids: Particles vibrate with the least kinetic energy.

• Liquids: Particles slide past one another with more kinetic energy than solids.

• Gases: Particles move freely and rapidly with the most kinetic energy.

Increasing the kinetic energy of molecules leads to a phase change, which is the transition between solid, liquid, and gas.

Evaporation occurs when liquid turns into gas at the surface of the liquid without significant additional energy.

⚛ Structure of the Atom

An atom has a nucleus with energy levels surrounding it.

• Nucleus: Contains neutrons (neutral charge) and protons (positive charge).

• Electrons: Orbit in energy shells around the nucleus, forming an electron cloud.

Most organisms are carbon-based life forms. After water, carbon is the most abundant element in living organisms.

🧂 Seawater Composition

Seawater is a mixture of different elements and compounds. Salinity refers to the concentration of dissolved solids and gases in the water.

Salinity varies depending on:

• Evaporation rates

• Inflow from melting ice

• River inputs

Major ions in seawater include:

Other minor elements found in seawater include bicarbonate, bromide, nitrate, silica, and iron, and even trace amounts of gold.

🌊 Water Molecule Bonding

Covalent Bonding 🤝

Covalent bonds involve the sharing of electrons, unlike ionic bonds where electrons are given and taken. In a water molecule, one oxygen atom and two hydrogen atoms are held together by covalent bonds.

• Oxygen has six valence electrons.

• Hydrogen has one valence electron.

When combined, they form a stable octet (eight electrons) for oxygen, making the molecule non-reactive.

Molecular Identification 🔬

Identify molecules based on the number of electrons and types of atoms.

• Water (H2O): One oxygen and two hydrogens, bent (V) shape. Often called "Mickey Mouse" due to its shape.

• Carbon Dioxide (CO2): One carbon and two oxygens, linear shape with two double bonds. It is very stable and used to put out fires.

• Oxygen (O2): A diatomic molecule with two oxygen atoms covalently bonded.

• Sulfur Dioxide (SO2): One sulfur and two oxygens, produced from burning fossil fuels and natural sources like hydrothermal vents and volcanoes (e.g., Kick 'em Jenny volcano in the West Indies).

• Glucose (C6H12O6): A ring or chain of carbons.

  • Made by plants and marine plants (sea grasses, algae) through photosynthesis.

  • Two glucose molecules form sucrose (table sugar).

  • Chains of glucose molecules form starch (in vegetables and breads).

  • Many glucose molecules together form cellulose (wood).

🧂 Ionic Bonding - Sodium Chloride (NaCl)

In ionic bonding, one atom gives an electron to another.

• Cation: Positive ion

• Anion: Negative ion

Cations and anions attract each other, like magnets.

Sodium Chloride Example:

• Sodium (Na) has one extra electron and gives it to chlorine.

• Chlorine (Cl) has seven electrons and takes one from sodium.

After this exchange, both ions have stable octets, making them stable. Sodium becomes a soft metal that explodes in water while chlorine is a deadly gas.

Ionic Bonds and Salts 🧪

Ionic bonds involve the transfer of electrons between atoms, creating ions with opposite charges that are attracted to each other.

Sodium Chloride (NaCl)

Sodium (Na) and chlorine (Cl) are individually hazardous: chlorine gas can cause lung failure and death, and sodium is a reactive metal. However, when they chemically bond, they form sodium chloride, or table salt.

• Sodium loses an electron, becoming positively charged (cation).

• Chlorine gains an electron, becoming negatively charged (anion).

• The electrostatic attraction between Na+ and Cl- forms the ionic bond.

Zooming in close enough to a grain of salt, you would be able to visualize the atoms that compose it. This arrangement of atoms in salt forms a crystalline structure.

Calcium Carbonate (CaCO3)

Calcium carbonate is very important for marine organisms like snails, crabs, and corals in making their shells.

• One calcium cation (Ca2+) with a charge of +2.

• Carbonate polyatomic molecule (CO32-) with a charge of -2.

• Chemical formula: CaCO3CaCO3​

Calcium carbonate dissolves in the ocean, allowing marine organisms to extract it and build their shells.

Other Salts

It's important to know the chemical names and formulas for these three salts: sodium chloride, magnesium sulfate, and calcium carbonate.

• Magnesium Sulfate (MgSO4MgSO4​):

  • Also known as Epsom salt.

  • Magnesium is a metal that burns brightly when ignited.

  • Magnesium sulfate can be used for soaking swollen feet.

• Calcium Carbonate (CaCO3CaCO3​):

  • Looks like white powder.

  • Sometimes sprinkled on chicken feed to provide calcium for harder eggshells.

Organisms and Calcium Carbonate

Many organisms need calcium carbonate to survive:

• Corals

• Shellfish (oysters, mussels, clams)

• Fish (for bones)

• Red seaweed

• Crustacean shells (lobsters, crabs, shrimp)

• Squid (pen shell)

Hydrogen Bonds 💧

Hydrogen bonds are responsible for many of water's unique properties. They occur due to the polarity of water molecules.

Polarity of Water

• Water molecules (H2OH2​O) are formed by covalent bonds.

• Oxygen is slightly negative and hydrogens are slightly positive.

• The negative oxygen side attracts the positive hydrogen side of another water molecule.

Hydrogen Bonding in Different States of Water

• Ice: Hydrogen bonds are stable, forming a crystalline structure that pushes out salts, making ice less dense and able to float.

• Liquid Water: Hydrogen bonds constantly break and reform due to kinetic energy, allowing water molecules to slide past each other.

• Gas (Steam): Kinetic energy overcomes hydrogen bonds, preventing them from forming.

Comparison with Covalent Bonds

Effect on Water Properties

Hydrogen bonding affects properties of water such as solvent action, density, and specific heat capacity.

• Solvent Action: Water is a universal solvent, dissolving many substances but not everything (e.g., sand, fats, and oils).

Solubility and Polarity 🧪

Water is a polar substance, making it effective at dissolving other polar substances, including gases. However, dissolving non-polar substances like fats, oils, and even carbon dioxide presents more of a challenge.

• Carbon Dioxide vs. Oxygen:

  • Carbon dioxide is significantly more soluble in water than oxygen.

  • Carbon dioxide is 200 times more soluble than oxygen.

  • This is because carbon dioxide is more polar than oxygen, leading to a stronger attraction between water and carbon dioxide molecules.

  • In a water environment inhabited by fish, the concentration of carbon dioxide will be higher than that of oxygen.

Factors Affecting Solubility 🌡

• Temperature: Solubility decreases as temperature increases (inverse relationship).

  • Heating water drives gases out. For example, in a tidal pool, as the sun heats the water, the levels of gases like oxygen and carbon dioxide decrease.

• Salinity: Solubility decreases as salinity increases (inverse relationship).

  • Adding more salt to water reduces the space available for gases to dissolve.

Density ⚖

• Lower temperature increases density.

  • Cold liquid water sinks, while warm water rises.

• Solid water (ice) is less dense than liquid water.

• Higher salinity increases density.

  • Saltwater sinks faster than freshwater.

Specific Heat Capacity 🔥

Water has a high specific heat capacity, meaning it can hold onto heat more effectively than other substances.

• It takes significantly more energy to change the temperature of water compared to other materials.

  • For example, a metal pot heats up much faster than a pot filled with water on a stove.

Solute, Solvent, Solution, and Solubility 💧

• Solute:

  The substance that dissolves (e.g., salt).

• Solvent:

  The substance doing the dissolving (e.g., water). Water is often referred to as the "universal solvent."

• Solution:

  The homogeneous mixture formed when a solute dissolves in a solvent. Homogeneous means that the mixture is uniform throughout, with the same composition in any sample.

• Solubility:

  The ability of a substance to dissolve in another substance. It defines how much solute can dissolve in a solvent at a certain temperature.

Microscopic Dissolution 🔬

When a solute like sodium chloride (salt) dissolves in water, the following occurs at the microscopic level:

• The cation, or positive sodium ion (Na+Na+), is "attacked" and surrounded by the partially negative oxygen portions of the water molecules (H2OH2​O).

• The anion, or negative chlorine ion (Cl−Cl−), is approached by the partially positive hydrogen sides of the water molecules.

• These interactions dissociate the ions, spreading them evenly throughout the water, leading to a homogeneous solution.