Atom: The smallest particle that can contain the chemical properties of an element.
Element: A substance composed of atoms that cannot be broken down into smaller, simpler components.
Structure of the Atom
An atom is composed of:
Protons: Positively charged particles found in the nucleus.
Neutrons: Neutral particles also found in the nucleus.
Electrons: Negatively charged particles that orbit around the nucleus.
General Chemistry Overview
Elements in Pure Form: Rare in nature; typically combine to form compounds.
Compound: Consists of two or more elements.
Chemical Properties: Determined by the electron arrangement. Atoms with incomplete shells interact with others to gain, lose, or share electrons.
Bonding of Atoms
Atoms bond to form molecules and compounds (e.g., Water - H2O and Carbon Dioxide - CO2).
Types of Chemical Bonds:
Ionic Bonds: Form when an atom loses or gains electrons, creating ions.
Covalent Bonds: Form when electrons are shared between atoms that lack an electrical charge.
Ionic Bonds
Formation occurs due to the transfer of electrons:
Cations: Positively charged ions that have lost electrons (e.g., Na+).
Anions: Negatively charged ions that have gained electrons (e.g., Cl-).
Example: Sodium Chloride (NaCl) results from the ionic bond between Na+ and Cl- due to their electrical attraction.
Covalent Bonds
Formed by sharing electrons, exemplified by Hydrogen gas (H2).
Mixtures: When atoms and molecules come together without reacting, they form mixtures, and an evenly distributed mixture is called a solution.
Types of Covalent Bonds
Nonpolar Covalent Bond: Electrons are shared equally.
Examples include hydrogen gas, oxygen gas, nitrogen gas, and methane gas.
Polar Covalent Bonds: Formed through the unequal sharing of electrons. Water is a prime example where oxygen is slightly electronegative, leading to its polar characteristics.
Water Molecule Structure
Composition: Water (H2O) consists of two hydrogen atoms and one oxygen atom.
Water is a polar molecule with a negative charge near oxygen and a positive charge near the hydrogen atoms.
Polarity allows water molecules to bond with each other and with other polar molecules and ions.
Characteristics of Polar Molecules
Polar molecules arise from unequal distribution of charges, resulting in a constant tug-of-war for shared electrons. Atoms with higher electronegativity draw electrons closer to their nucleus.
This results in a higher concentration of electrons near the oxygen atom, imparting a slight negative charge to oxygen and slight positive charges to hydrogen.
Properties of Water
Cohesion: Due to hydrogen bonds, water adheres to itself, allowing it to transport nutrients in plants.
Surface Tension: Water's cohesive properties contribute to high surface tension, which measures the difficulty of breaking the surface of a liquid.
Hydrogen Bonds: Very weak compared to ionic and covalent bonds but collectively strong, enabling several properties of water.
Water as a Solvent
Water adheres to other polar molecules, and ionic compounds like table salt dissociate due to electrostatic attraction between water molecules and ions (Na+ and Cl-).
States of Water
Three States of Matter:
Solid (Ice): Molecules locked in place due to stable hydrogen bonds.
Liquid (Water): Molecules move freely with some hydrogen bonds present.
Gas (Vapor): Rapidly moving independent molecules without hydrogen bonds.
Unique Properties of Water
High Specific Heat: Requires large amounts of energy to change temperature.
High Heat of Vaporization: Evaporation causes cooling.
Density: Solid water is less dense than liquid water, leading to ice floating on water.
Good Solvent: Can dissolve polar molecules and ions.
Organizes Nonpolar Molecules: Results in hydrophilic (water-loving) and hydrophobic (water-fearing) behaviors.
Ion Formation: Water can dissociate to form hydroxide (OH-) and hydrogen (H+) ions.
Implications for Marine Life
Water’s thermal properties prevent drastic temperature changes, allowing stable conditions for marine organisms, whereas shallow ecosystems are more vulnerable.
Hydrogen Bonding Effects
Water absorbs a significant amount of heat due to its hydrogen bonds, with heat increasing the movement of molecules and braking bonds, while cooling forms bonds and releases energy.
Global Thermostatic Effects
Water moderates Earth's surface temperature, preventing equatorial oceans from boiling and polar oceans from freezing solid, facilitating life on Earth.
Climate and Evaporation Patterns
The tropics are humid and receive more rainfall than evaporates; temperate regions experience less precipitation; polar regions have low evaporation relative to precipitation.
Heat Exchange Mechanisms
Heat removed from tropical oceans is transported towards the poles and released at higher latitudes through precipitation, impacting climate.
Composition of Seawater
Seawater contains sufficient salt to cover the planet with a thickness greater than 500 feet, primarily coming from geological weathering and volcanic outgassing.
Salinity Measurement: Measured in parts per thousand (ppt). For example, seawater typically has 35 grams of salt per 1,000 grams of water.
Seawater Salinity
An average salinity of 3.5% indicates 96.5% pure water and 3.5% solutes. Six ions make up 99% of seawater solids.
Main solutes: Sodium (Na+) and Chloride (Cl-) comprise 85% of seawater.
Sources of Seawater Salt
Rivers supply most of the salt; volcanic activity and weathering of sedimentary rocks contribute ions, while out-gassing from volcanic eruptions provides various gases.
Salinity Measurement Techniques
Conductivity of seawater indicates its salinity, which significantly influences water density.
Water Density Influences
Denser saltwater sinks below freshwater; cold water can trap more nutrients.
Dissolved Gases in Seawater
Major gases include Nitrogen (N2), Oxygen (O2), and Carbon Dioxide (CO2).
Nitrogen in Seawater
Comprises ~48% of dissolved gases but is mostly unusable in N2 form. Its reactive forms include nitrite (NO2), nitrate (NO3), and ammonium (NH4).
Oxygen in Seawater
Essential for aerobic organisms, constituting ~36% of dissolved gases, produced primarily through photosynthesis.
Carbon Dioxide in Seawater
Accounts for ~15% of dissolved gases and increases in concentration with water depth.
Acid-Base Balance in Seawater
Water separates into hydroxide (OH-) and hydrogen ions (H+); an imbalance leads to acidity or basicity as measured by pH (average seawater pH 7.8).
Carbonate Buffering System
CO2 dissolves in seawater forming carbonic acid, allowing the ocean to buffer changes in acidity and alkalinity, maintaining ecosystem stability.
Impact of Human Activities on Ocean Chemistry
Increased atmospheric CO2 leads to higher levels in seawater, promoting ocean acidification which affects calcifying organisms’ ability to form shells.
Long-term Environmental Impacts
Regions like New York, with significant shellfish industries, are at risk from the effects of acidification, potentially affecting economic and ecological stability.
Economic Implications for Shellfish Industry
New York relies heavily on shellfish, averaging $24 million annually over the past decade, highlighting the significance of aquaculture in local economies and the potential threats from ocean changes.