Chapter 2: Scientific Inquiry and Chemistry of Life

Scientific Method and Data Types

The scientific method is a systematic approach used in biology to investigate natural phenomena. It involves making observations, forming hypotheses, conducting experiments, and analyzing data.

• Qualitative Data: Descriptive data that characterizes but does not measure attributes, properties, or phenomena (e.g., color, texture).

• Quantitative Data: Numerical data that can be measured and quantified (e.g., length, mass, temperature).

• Hypothesis: A testable statement or prediction based on observations.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

• Controls: Experimental elements used to minimize the effects of variables other than the independent variable. Negative control shows what happens in the absence of the experimental treatment; positive control confirms the expected effect.

Inductive Reasoning involves making generalizations from specific observations, while deductive reasoning uses general principles to predict specific outcomes.

Atoms and Elements

Atoms are the basic units of matter, composed of protons, neutrons, and electrons. Elements are substances consisting of only one type of atom.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• Atomic Number: Number of protons in an atom, determines the element.

• Mass Number: Sum of protons and neutrons.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Valence Shell: The outermost electron shell, determines chemical reactivity.

To determine the number of protons, electrons, and neutrons in an atom:

• Protons = Atomic Number

• Electrons = Atomic Number (in a neutral atom)

• Neutrons = Mass Number - Atomic Number

Chemical Bonds and Interactions

Chemical bonds hold atoms together in molecules and compounds. The type of bond affects the properties of the substance.

• Covalent Bond: Atoms share electrons. Can be nonpolar (equal sharing) or polar (unequal sharing).

• Ionic Bond: Electrons are transferred from one atom to another, creating ions that attract each other.

• Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen, nitrogen).

• Van der Waals Interactions: Weak attractions due to transient local partial charges.

Electronegativity is the tendency of an atom to attract electrons in a bond. It determines bond polarity.

Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new substances. They are represented by chemical equations.

• Reactants: Substances present before the reaction.

• Products: Substances formed by the reaction.

• Balancing Equations: Ensures equal numbers of each atom on both sides of the equation.

Example equation (balanced):

Properties of Water and Solutions

Water: Structure and Importance

Water is essential for life due to its unique chemical and physical properties.

• Polar Molecule: Water has a partial positive charge on hydrogen and partial negative on oxygen, leading to polarity.

• Cohesion: Attraction between water molecules due to hydrogen bonding.

• Adhesion: Attraction between water molecules and other substances.

• Specific Heat: Amount of heat required to raise the temperature of 1 gram of a substance by 1°C. Water's high specific heat stabilizes temperatures.

• Heat of Vaporization: Energy required to convert water from liquid to gas.

• Evaporative Cooling: As water evaporates, it removes heat, cooling surfaces.

Solutions, Solutes, and Solvents

Solutions are homogeneous mixtures of two or more substances.

• Solvent: The substance that dissolves the solute (water is the universal solvent).

• Solute: The substance dissolved in the solvent.

• Hydrophilic: Substances that dissolve well in water (water-loving).

• Hydrophobic: Substances that do not dissolve well in water (water-fearing).

Acids, Bases, and Buffers

Acids and bases affect the pH of solutions, which is crucial for biological processes.

• Acid: Substance that increases hydrogen ion concentration () in solution.

• Base: Substance that decreases hydrogen ion concentration.

• pH: Measure of hydrogen ion concentration;

• Buffer: Substance that minimizes changes in pH by accepting or donating hydrogen ions.

Mole: Unit for amount of substance; 1 mole = particles (Avogadro's number).

Molarity (M): Concentration of solute in solution;

Organic Molecules and Functional Groups

Carbon Chemistry and Diversity

Carbon's electron configuration allows it to form four covalent bonds, enabling the creation of large, complex, and diverse organic molecules.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen.

• Carbon Skeletons: Can vary in length, branching, and ring structures, contributing to molecular diversity.

Isomers

Isomers are compounds with the same molecular formula but different structures.

• Structural Isomers: Differ in the covalent arrangement of atoms.

• Geometric Isomers: Differ in spatial arrangement around a double bond.

• Enantiomers: Mirror-image isomers, important in biological systems.

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms within molecules that confer particular chemical properties.

Recognizing these groups is essential for understanding the function and reactivity of organic molecules.

Additional info: Academic context and definitions have been expanded for clarity and completeness. Table entries for functional groups are inferred from standard biology curriculum.