Chapter 1 - The Structure and Stability of Atoms

Periodic Table and Element Properties

The periodic table is a fundamental tool in chemistry, organizing elements by increasing atomic number and grouping them by similar properties. Understanding its structure allows prediction of chemical and physical behaviors.

• Atomic Number: The number of protons in an atom, unique to each element.

• Element Symbol: One- or two-letter abbreviation for each element (e.g., H for hydrogen).

• Atomic Weight: The weighted average mass of an element's isotopes.

• Groups/Families: Vertical columns; elements in the same group share similar properties (e.g., alkali metals, halogens, noble gases).

• Classification: Elements are classified as metals, nonmetals, or metalloids based on their properties.

• Predicting Properties: Position in the table helps predict reactivity, state, and other properties.

• Example: Sodium (Na) is an alkali metal, highly reactive, and found in Group 1.

Mass and Proportion Laws

Three fundamental laws govern mass relationships in chemical reactions and compounds.

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.

• Law of Definite Proportions: A chemical compound always contains the same elements in the same proportion by mass.

• Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

• Example: Water (H2O) always has a mass ratio of hydrogen to oxygen of about 1:8.

Atomic Structure and Historical Experiments

The internal structure of the atom was revealed through key experiments.

• Protons, Neutrons, Electrons: Atoms consist of a nucleus (protons and neutrons) surrounded by electrons.

• Thomson's Cathode-Ray Experiment: Discovered the electron, showing atoms contain negatively charged particles.

• Millikan's Oil-Drop Experiment: Measured the charge of the electron.

• Rutherford's Gold-Foil Experiment: Revealed the nucleus, showing most of the atom's mass is concentrated in a small, positively charged center.

• Example: Rutherford's experiment led to the nuclear model of the atom.

Isotope Symbols and Identification

Isotopes are atoms of the same element with different numbers of neutrons. Isotope symbols provide information about atomic structure.

• Isotope Symbol: Written as AZElement, where A is mass number, Z is atomic number.

• Protons: Equal to atomic number (Z).

• Neutrons: Equal to mass number (A) minus atomic number (Z).

• Electrons: Equal to protons in a neutral atom; adjusted for charge in ions.

• Identifying Isotopes: Isotopes have the same Z but different A.

• Example: 146C and 126C are isotopes of carbon.

Average Atomic Mass

The average atomic mass of an element is calculated from the masses and abundances of its isotopes.

• Weighted Average:

• Percent Abundance: The proportion of each isotope in nature.

• Inferring Abundance: The isotope with mass closest to the atomic weight is usually most abundant.

• Example: Chlorine has two main isotopes: 35Cl and 37Cl. Its atomic weight (~35.5) suggests 35Cl is more abundant.

Mole Conversions

The mole is a counting unit in chemistry, relating mass, number of particles, and moles.

• Mole: One mole contains particles (Avogadro's number).

• Conversions:

  • Mass to moles:

  • Moles to atoms:

• Example: 12 g of carbon () contains 1 mole, or atoms.

Chapter 2 - Periodicity and the Electronic Structure of Atoms

Wave-Energy Conversions

Electromagnetic radiation exhibits wave-like properties, and its energy can be related to wavelength and frequency.

• Wavelength (): Distance between two consecutive peaks.

• Frequency (): Number of cycles per second (Hz).

• Energy of a Photon:

• Speed of Light:

• Example: A photon with nm has and .

Line Spectra and the Bohr Model

The hydrogen emission spectrum consists of discrete lines due to quantized electron energy levels.

• Quantized Energy Levels: Electrons occupy specific energy levels; transitions between levels emit/absorb photons.

• Bohr Model: Electrons orbit the nucleus in fixed paths; energy is quantized.

• Highest/Lowest Energy Transitions: Largest energy change corresponds to shortest wavelength (highest energy photon).

• Example: Transition from to emits a photon; $n=2$ to emits a higher-energy photon.

de Broglie Wavelength

Matter exhibits both particle-like and wave-like behavior, as described by de Broglie's hypothesis.

• de Broglie Equation:

• Mass (): Mass of the particle.

• Velocity (): Speed of the particle.

• Example: An electron moving at m/s has a wavelength calculated by de Broglie's equation.

Quantum Numbers and Atomic Orbitals

Quantum numbers describe the properties and locations of electrons in atoms.

• Principal Quantum Number (): Energy level (shell).

• Angular Momentum Quantum Number (): Shape of orbital (s: , p: , d: ).

• Magnetic Quantum Number (): Orientation of orbital.

• Spin Quantum Number (): Electron spin ( or ).

• Orbital Shapes: s (spherical), p (dumbbell), d (cloverleaf).

• Example: An electron in a 2p orbital: , , , .

Electron Configurations

Electron configurations describe the arrangement of electrons in an atom, following specific rules.

• Pauli Exclusion Principle: No two electrons in an atom can have the same set of quantum numbers.

• Hund's Rule: Electrons fill degenerate orbitals singly before pairing.

• Ground-State Configuration: Lowest energy arrangement of electrons.

• Example: Oxygen:

Periodic Trends

Periodic trends arise from electron configuration and effective nuclear charge, affecting atomic size, ionization energy, and reactivity.

• Atomic Size: Decreases across a period, increases down a group.

• Ionization Energy: Increases across a period, decreases down a group.

• Reactivity: Metals become more reactive down a group; nonmetals become more reactive across a period.

• Effective Nuclear Charge (): Net positive charge experienced by valence electrons.

• Example: Sodium is larger and more reactive than chlorine; chlorine has higher ionization energy.