Chemistry of Life: Creating Compounds

Elements, Atoms, and Compounds

All living organisms are composed of matter, which consists of elements and compounds. Understanding the basic chemical building blocks is essential for studying biological processes.

• Element: A substance that cannot be broken down or converted into other substances by chemical means.

• Atom: The smallest particle of an element that retains its chemical properties.

• Compound: A substance consisting of two or more elements in a fixed ratio, exhibiting emergent properties distinct from its constituent elements.

Elements of Life

Only a fraction of the 92 naturally occurring elements are essential for life. Organisms require these elements to survive, grow, and reproduce.

• Essential elements: 20-25% of natural elements are required for life.

• Trace elements: Needed in minute quantities (e.g., iodine for thyroid function).

• Deficiency example: Lack of iodine can cause goiter in humans.

Evolution of Tolerance to Toxic Elements

Some organisms have evolved mechanisms to tolerate or detoxify toxic elements in their environment. This adaptation is significant in ecological restoration.

• Phytoremediation: The use of plants (e.g., sunflowers) to absorb and detoxify heavy metals from contaminated soils.

• Application: Sunflowers were used to clean soils after Hurricane Katrina.

Element Properties Depend on Atomic Structure

Subatomic Particles

The properties of elements are determined by the structure of their atoms, which are composed of subatomic particles.

• Neutrons: No electrical charge.

• Protons: Positive charge.

• Electrons: Negative charge; form a cloud around the nucleus.

• Atomic nucleus: Contains protons and neutrons.

Atomic Number and Atomic Mass

Atoms of different elements vary in their number of subatomic particles. These differences define their chemical identity and mass.

• Atomic number: Number of protons in the nucleus.

• Mass number: Sum of protons and neutrons in the nucleus.

• Atomic mass: Approximated by the mass number.

Isotopes

Isotopes are variants of elements with different numbers of neutrons. Some isotopes are radioactive and have important biological and medical applications.

• Isotope: Atomic forms of an element differing in neutron number.

• Radioactive isotope: Nucleus decays spontaneously, emitting particles and energy.

• Uses: Dating fossils, tracing metabolic processes, medical diagnostics (e.g., PET scans).

• Hazards: Radioactive fallout can damage cellular molecules.

Energy and Electrons

Potential Energy and Electron Shells

Energy is the capacity to cause change. Electrons possess potential energy based on their position relative to the nucleus, and their arrangement in shells influences chemical behavior.

• Potential energy: Energy due to location or structure.

• Electron shells: Electrons occupy shells with varying energy levels.

• Electron transitions: Electrons absorb or release energy to move between shells.

Electrons & Chemical Bonds

Valence Electrons and Reactivity

The chemical behavior of atoms is determined by the electrons in their outermost shell (valence shell). Atoms with incomplete valence shells are reactive and form chemical bonds.

• Inert atoms: Completed valence shells; unreactive.

• Reactive atoms: Incomplete valence shells; form bonds by sharing or transferring electrons.

Covalent Bonds

Covalent bonds involve the sharing of valence electrons between atoms, resulting in the formation of molecules.

• Covalent bond: Sharing of a pair of valence electrons.

• Single bond: One pair of electrons shared.

• Double bond: Two pairs of electrons shared.

Electronegativity & Covalent Bonds

Electronegativity is the tendency of an atom to attract electrons. It influences the polarity of covalent bonds, affecting molecular properties.

• Electronegativity: Measure of an atom's ability to attract electrons.

• Polar covalent bond: Unequal sharing of electrons due to differences in electronegativity.

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.

• Cation: Positively charged ion (lost electron).

• Anion: Negatively charged ion (gained electron).

• Ionic bond: Attraction between cation and anion.

• Ionic compounds: Also called salts.

Weak Chemical Interactions

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom nearby. They are crucial for the structure and function of biological molecules.

• Hydrogen bond: Noncovalent attraction between hydrogen and an electronegative atom.

• Polar covalent bonds: Cause partial charges, enabling hydrogen bonding.

• Biological importance: Many weak interactions collectively stabilize biological structures.

Van der Waals Interactions

Van der Waals interactions are weak attractions due to transient asymmetrical electron distributions. They are significant when many such interactions occur simultaneously.

• Van der Waals interaction: Weak attraction between molecules or atoms in close proximity.

• Example: Gecko's ability to walk on walls due to numerous van der Waals interactions between its toe hairs and surfaces.

Chemical Reactions

Making and Breaking Chemical Bonds

Chemical reactions involve the formation and breaking of chemical bonds, transforming reactants into products. Photosynthesis is a key biological reaction.

• Reactants: Starting molecules.

• Products: Final molecules.

• Photosynthesis equation:

Hydrogen Bonding & Water

Properties of Water

Water's unique properties arise from hydrogen bonding, making it essential for life. These properties include cohesion, adhesion, surface tension, temperature moderation, and its role as a solvent.

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules cling to other substances.

• Surface tension: Difficulty in breaking the surface of water due to ordered hydrogen bonds.

• Temperature moderation: Water absorbs and releases heat with minimal temperature change.

• Expansion upon freezing: Ice is less dense than liquid water, allowing it to float.

• Versatility as a solvent: Water dissolves many substances, supporting biochemical reactions.

Cohesion and Adhesion in Water Transport

Cohesion and adhesion are critical for the transport of water and nutrients in plants, especially against gravity.

• Cohesion: Hydrogen bonding keeps water molecules together.

• Adhesion: Water adheres to cell walls, counteracting gravity.

Surface Tension

Surface tension is a result of cohesion at the air-water interface, giving water an unusually high surface tension. This property allows certain organisms to walk on water.

• Surface tension: Measure of how hard it is to break the surface of a liquid.

• Biological example: Some insects can walk on water due to surface tension.

Moderation of Temperature by Water

Water's high specific heat allows it to absorb and release heat, moderating temperature in environments and organisms.

• Heat absorption: Water absorbs heat from warmer air.

• Heat release: Water releases stored heat to cooler air.

• Biological impact: Helps maintain stable temperatures in organisms and ecosystems.

Floating of Ice on Liquid Water

Ice floats because hydrogen bonds in ice are more ordered, making it less dense than liquid water. This property is vital for aquatic life.

• Insulation: Floating ice insulates water below, allowing life to persist under frozen surfaces.

• Ecological importance: Prevents bodies of water from freezing solid.

Water: The Solvent of Life

Solutions, Solvents, and Solutes

Water is known as the universal solvent due to its ability to dissolve a wide range of substances, facilitating biochemical reactions.

• Solution: Homogeneous mixture of substances.

• Solvent: Dissolving agent (water in aqueous solutions).

• Solute: Substance dissolved in the solvent.

• Aqueous solution: Solution where water is the solvent.

Water as a Solvent

Water dissolves ionic and polar compounds due to its polarity. Substances are classified based on their affinity for water.

• Hydrophilic: Affinity for water; dissolves easily.

• Hydrophobic: No affinity for water; does not dissolve (e.g., oils).

Acids, Bases, & pH

Acids, Bases, and pH Scale

The pH scale measures the concentration of hydrogen ions in a solution, affecting biological processes and molecular interactions.

• Acids: Increase H+ concentration (pH < 7).

• Bases: Decrease H+ concentration (pH > 7).

• Biological fluids: Most have pH between 6 and 8; internal pH of cells is close to 7.

• Buffers: Substances that minimize changes in H+ or OH- concentrations, maintaining pH stability.

Summary Table: Types of Chemical Bonds

Additional info: Academic context was added to clarify definitions, examples, and biological relevance for each topic.