Covalent Bonds and Chemical Reactions

Covalent Bonds

  • Definition: Covalent bonds involve the sharing of electrons between atoms, creating strong bonds.

    • Metaphor: Covalent connections can be likened to cohabitation—sharing resources (like electrons) is essential for bonding, similar to sharing dinner with a spouse.

Types of Covalent Bonds

  • Single Covalent Bond: Involves the sharing of one pair of electrons (2 electrons total).

  • Double Covalent Bond: Involves the sharing of two pairs of electrons (4 electrons total).

  • Triple Covalent Bond: Involves the sharing of three pairs of electrons (6 electrons total).

    • Note: The strength of the bond increases with the number of electron pairs shared.

Electron Sharing Dynamics

  • Electrons oscillate back and forth between bonded atoms, creating a shared pattern around the nucleus.

  • Covalent bonds can be drawn through models such as the electron shell model or represented through chemical formulas.

Unequal Electron Sharing

  • Distinction between Nonpolar and Polar Covalent Bonds:

    • Nonpolar Covalent Bond: Electrons are shared equally between atoms.

    • Example: Electrons oscillate between two equal nuclei, represented by equivalent sharing (e.g., equal receiving of dollars).

    • Polar Covalent Bond: Electrons are shared unequally, favoring the atom with greater nuclear charge (more protons attract electrons).

    • Example: Between hydrogen (1 proton) and oxygen (more than 1 proton), electrons spend more time near oxygen, leading to partial charges—oxygen becomes slightly negative (δ−) and hydrogen slightly positive (δ+).

    • Polar Molecules: Molecules like water exhibit a bent structure due to the uneven charge distribution, analogous to the Earth's geographic poles (one negatively charged and one positively charged).

Water as a Polar Molecule

  • Water is a quintessential polar molecule, where oxygen's greater electronegativity causes a bending structure and unequal charge distribution, facilitating hydrogen bond formation:

    • Oxygen attracts electrons more than hydrogen, inducing a slight negative charge at the oxygen and a slight positive charge at the hydrogens.

Hydrogen Bonds

  • Definition: A hydrogen bond is an attractive interaction between a hydrogen atom bonded to a more electronegative atom and another electronegative atom.

    • Character: These bonds are relatively weak individually but can create substantial forces when numerous hydrogen bonds exist.

  • Cohesion and Adhesion: Due to hydrogen bonds, water exhibits strong cohesive forces (molecules sticking together) leading to surface tension, which explains phenomena like a spider walking on water.

States of Matter

  • Solid: Has constant volume and shape (e.g., a water bottle).

  • Liquid: Constant volume but conforms to the shape of its container.

  • Gas: Changes in both volume and shape (e.g., opening a soda can releases gas, allowing it to expand into the entirety of its surroundings).

Chemical Reactions

  • Definition: A chemical reaction involves breaking and forming bonds, transforming reactants into products.

    • Reactants: Original substances that undergo change.

    • Products: Substances produced by the chemical reaction.

  • Example Terms:

    • Metabolism: Sum total of all chemical reactions in the body.

    • Energy: Measurement of work capacity.

  • Energy types:

    • Kinetic Energy: Energy of motion.

    • Potential Energy: Stored energy based on an object's position.

    • Example: A roller coaster at its peak has high potential energy due to gravity.

    • Chemical Energy: Potential energy stored in chemical bonds, released during chemical reactions (e.g., food consumed providing energy).

Types of Chemical Reactions

  1. Decomposition: Breaking down larger molecules into smaller components.

    • Example: AB → A + B

  2. Synthesis: Combining smaller molecules to form larger ones.

    • Example: A + B → AB

  3. Exchange: A reaction where bonds are both broken and formed, involving both decomposition and synthesis.

    • Example: AB + CD → AC + BD

  4. Reversible: Can transition in both directions.

    • Denoted by a double-headed arrow (↔).

Specifics to Reactions

  • Catabolism: Biological reactions that involve breaking down molecules (decomposition).

  • Anabolism: Biological processes that involve building up molecules (synthesis).

    • Hydrolysis: Water is used to break down chemical bonds (decomposition). E.g., AB + H2O → A + BOH.

    • Dehydration Synthesis/Condensation: Building larger molecules by removing water. E.g., A + B → AB + H2O.

Enzymes in Reactions

  • Enzymes are catalysts that lower the activation energy required for a chemical reaction, thereby accelerating the reaction.

  • Key Properties:

    • Enzymes are not consumed in reactions; they remain unchanged post-reaction.

  • The activation energy is the energy needed to initiate the reaction—metaphorically, it’s like a nudge that gets things moving.

Exergonic vs Endergonic Reactions

  • Exergonic: Releases energy (exothermic).

  • Endergonic: Absorbs energy (endothermic).

Organic and Inorganic Compounds

  • Organic Compounds: Contain carbon and hydrogen (e.g., nucleic acids, proteins, lipids, carbohydrates).

  • Inorganic Compounds: Generally do not contain carbon-hydrogen structures (e.g., water, salts).

Solutions and Mixtures

  • Solution: A homogeneous mixture of solute (material being dissolved) and solvent (dissolving medium, usually liquid).

  • Colloid: A mixture where particles are dispersed but not settled out (e.g., milk).

  • Suspension: Larger particles that settle over time (e.g., blood).

pH Scale and Acids/Bases

  • pH scale ranges from 0 to 14:

    • 0 indicates acidity, 7 is neutral, 14 indicates alkalinity.

    • Acid: Proton donor (increases hydrogen ions in solution).

    • Base: Proton acceptor (reduces hydrogen ions in solution).

  • Strong acids dissociate fully; weak acids partially dissociate.

Buffers and Homeostasis

  • Buffers minimize changes in pH by neutralizing strong acids/bases, usually consisting of a weak acid and its conjugate base.

  • Example: Tums acts as a buffer to reduce acidity after spicy meals.

Biological Macromolecules

  • Monomers and Polymers:

    • Monomer: Individual units (one).

    • Polymer: Multiple monomers linked together.

  • Types of biological macromolecules include:

    • Carbohydrates:

    • Monomer: Monosaccharides (e.g., glucose, fructose).

    • Polymer: Polysaccharides (e.g., starch, glycogen).

    • Proteins:

    • Monomer: Amino acids.

    • Polymer: Polypeptides.

    • Lipids:

    • Fatty acids lead to triglycerides, phospholipids.

Fatty Acids and Saturation

  • Saturated vs Unsaturated Fatty Acids:

    • Saturated: Every carbon has four bonds, allowing no room for additional hydrogen.

    • Unsaturated: Contains double bonds between carbons, creating kinks and preventing tight packing.

  • Unsaturated fats are typically liquid at room temperature, while saturated fats are solid.