General Chemistry: Foundations and Core Concepts

Chemistry in Context

Introduction to Chemistry

Chemistry is the scientific study of the composition, properties, and interactions of matter. It is a foundational science that connects to many other scientific disciplines and is essential for understanding the material world.

• Definition: Chemistry investigates substances, their properties, and how they change during chemical reactions.

• Historical Development:

  • Ancient Greeks proposed that matter consisted of four elements: earth, air, fire, and water.

  • Alchemists (circa 1580) attempted to transform base metals into noble metals, contributing practical techniques but lacking scientific rigor.

• Chemistry as the Central Science: Chemistry is interconnected with biology, physics, medicine, engineering, environmental science, and more. Understanding chemistry is crucial for progress in these fields.

• Importance in Everyday Life: Chemistry is involved in digestion, manufacturing materials (e.g., polymers), refining fuels, and countless other daily processes.

The Scientific Method

The scientific method is a systematic approach to investigation, based on observation and experimentation.

• Steps: Observation, hypothesis formation, experimentation, analysis, and conclusion.

• Hypothesis: A tentative explanation for observations.

• Theory: A well-substantiated, comprehensive, and testable explanation of aspects of nature.

• Law: A concise statement summarizing a vast number of experimental results and observations.

Domains of Chemistry

Chemists study matter in three conceptual domains:

• Macroscopic: Observable phenomena (e.g., color, state, volume).

• Microscopic: Atoms, molecules, and particles, often visualized with microscopes or models.

• Symbolic: Chemical symbols, formulas, and equations used to represent substances and processes.

Phases and Classification of Matter

States of Matter

Matter exists in several physical states, each with distinct properties.

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume but takes the shape of its container; particles are less tightly packed and can move past each other.

• Gas: No definite shape or volume; particles are far apart and move freely.

• Plasma: A high-energy state with charged particles, found in stars and lightning.

Mass vs. Weight

• Mass: The amount of matter in an object; measured in kilograms (kg) or grams (g); does not change with location.

• Weight: The force exerted by gravity on an object; depends on location (e.g., Earth vs. Moon).

Law of Conservation of Matter

The total quantity of matter remains constant during physical and chemical changes.

• Statement: Matter is neither created nor destroyed in a chemical reaction.

Classification of Matter

• Pure Substances: Have constant composition and properties.

  • Elements: Cannot be broken down by chemical means (e.g., gold, oxygen).

  • Compounds: Composed of two or more elements chemically bonded (e.g., H2O, CO2).

• Mixtures: Combinations of two or more substances that can be separated by physical means.

  • Homogeneous Mixture (Solution): Uniform composition throughout (e.g., saltwater).

  • Heterogeneous Mixture: Non-uniform composition (e.g., salad dressing).

Atoms and Molecules

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

• Molecule: Two or more atoms bonded together (e.g., O2, H2O).

Physical and Chemical Properties

Physical Properties and Changes

Physical properties can be observed without changing the chemical identity of a substance.

• Examples: Density, color, melting point, boiling point, electrical conductivity.

• Physical Change: Alters the state or appearance but not the composition (e.g., melting, freezing, dissolving).

Chemical Properties and Changes

Chemical properties describe a substance's ability to undergo changes that transform it into different substances.

• Examples: Flammability, reactivity, toxicity, acidity.

• Chemical Change: Produces one or more new substances (e.g., rusting, combustion).

Extensive vs. Intensive Properties

• Extensive Properties: Depend on the amount of matter (e.g., mass, volume, heat).

• Intensive Properties: Independent of the amount of matter (e.g., density, temperature).

Atomic Structure and Symbolism

Structure of the Atom

Atoms consist of a dense nucleus surrounded by electrons.

• Nucleus: Contains protons (positive charge) and neutrons (neutral); most of the atom's mass.

• Electrons: Negatively charged particles occupying most of the atom's volume.

• Relative Sizes: Atomic diameter ~ $10^{-10}$ m; nucleus diameter ~ $10^{-15}$ m.

Subatomic Particles

Particle	Mass (amu)	Charge
Proton	1.0073	+1
Neutron	1.0087	0
Electron	0.00055	-1

Atomic Number, Mass Number, and Isotopes

• Atomic Number (Z): Number of protons; defines the element.

• Mass Number (A): Total number of protons and neutrons: $A = Z + N$

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

• Symbolism: $^{A}_{Z}X$ (where X is the element symbol)

Ions

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Charge Calculation: $\text{Charge} = \text{Number of protons} - \text{Number of electrons}$

Atomic Mass and Isotopic Abundance

• Atomic Mass Unit (amu): $1\ \text{amu} = 1.6605 \times 10^{-24}\ \text{g}$

• Average Atomic Mass: Weighted average of all isotopes: $\text{Average mass} = \sum (\text{fractional abundance} \times \text{isotopic mass})$

• Example (Boron): $\text{Average mass} = (0.199 \times 10.0129) + (0.801 \times 11.0093) = 10.81\ \text{amu}$

The Periodic Table

Development and Organization

The periodic table arranges elements by increasing atomic number and groups elements with similar properties together.

• Periodic Law: The properties of elements are periodic functions of their atomic numbers.

• Periods: Horizontal rows (numbered 1-7).

• Groups: Vertical columns (numbered 1-18).

Classification of Elements

• Metals: Shiny, malleable, good conductors of heat and electricity.

• Nonmetals: Dull, poor conductors.

• Metalloids: Properties intermediate between metals and nonmetals.

Special Groups

• Alkali Metals: Group 1 (except hydrogen)

• Alkaline Earth Metals: Group 2

• Transition Metals: Groups 3-12

• Halogens: Group 17

• Noble Gases: Group 18

• Lanthanides and Actinides: Two rows at the bottom

Element Symbols

• Each element is represented by a one- or two-letter symbol (e.g., H for hydrogen, Fe for iron).

• Symbols are derived from English or Latin names.