Introduction to Atomic Structure and Basic Chemical Principles

What is Science and Chemistry?

Definitions and Scope

• Science: The study of the physical and natural world through observations and experiments.

• Chemistry: The study of matter and its transformations. Matter is composed of atoms.

Classification of Matter

• Pure Substances:

  • Elements: Substances that cannot be broken down into simpler substances by chemical means.

  • Compounds: Substances composed of two or more elements in a fixed, whole-number ratio.

• Mixtures:

  • Homogeneous: Uniform composition throughout (solutions).

  • Heterogeneous: Non-uniform composition.

The Atomic Theory

Dalton's Atomic Theory

• Matter is composed of extremely small particles called atoms.

• An element consists of only one type of atom.

• Atoms of one element differ in properties from atoms of all other elements.

• A compound consists of atoms of two or more elements combined in a small, whole-number ratio.

• Atoms are neither created nor destroyed during a chemical change.

Dalton's Model and Laws

• Law of Conservation of Matter: Matter is neither created nor destroyed.

• Law of Constant Composition: A given compound always contains the same proportion of elements by mass.

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

Atomic Structure: Historical Experiments

Discovery of Subatomic Particles

• J.J. Thomson: Discovered the electron using the cathode ray tube experiment, showing that atoms are divisible and contain negatively charged particles.

• R.A. Millikan: Measured the charge of the electron with the oil drop experiment.

• Thomson's Plum Pudding Model: Proposed that electrons are embedded in a positively charged sphere.

Modern Atomic Model: The Nuclear Atom

• Based on Rutherford's gold foil experiment, the atom consists of a small, dense, positively charged nucleus surrounded by electrons.

Subatomic Particles Table

Particle	Mass (kg)	Charge (1.6 x 10-19 C)
Electron	9.11 x 10-31	-1
Proton	1.67 x 10-27	+1
Neutron	1.67 x 10-27	0

Atomic Symbols and Isotopes

Atomic Symbols

• General form: AZX, where A is the mass number (protons + neutrons), Z is the atomic number (protons), and X is the chemical symbol.

Isotopes

• Atoms of the same element with the same number of protons but different numbers of neutrons.

• Example: 12C, 13C, 14C (all carbon isotopes).

Ions

• An atom or group of atoms that carries a net positive or negative charge.

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

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

The Periodic Table and Elements

Periodic Table Organization

• Elements are arranged by increasing atomic number.

• Groups (columns) and periods (rows) classify elements with similar properties.

Oxidation Numbers

Rule	Oxidation Number
Free element	0
Group 1A	+1
Group 2A	+2
Fluorine	-1
Oxygen (most compounds)	-2
Hydrogen (with nonmetals)	+1

Naming Compounds and Writing Formulas

Ionic Compounds

• Formed from metal and non-metal ions.

• Monatomic ions: Use the element name for cations and add '-ide' for anions.

• Polyatomic ions: Use the name of the polyatomic ion.

Examples

• Ca3N2: Calcium nitride

• FeCl2: Iron(II) chloride

• BaCl2: Barium chloride

• NaClO: Sodium hypochlorite

• Li3PO4: Lithium phosphate

Covalent Compounds

• Formed from non-metal and non-metal elements.

• Prefixes indicate the number of each atom (mono-, di-, tri-, etc.).

Examples

• N2O: Dinitrogen monoxide

• SF6: Sulfur hexafluoride

• N2O5: Dinitrogen pentoxide

Acids

• Binary acids: Contain hydrogen and one other nonmetal (e.g., HCl = hydrochloric acid).

• Oxyacids: Contain hydrogen, oxygen, and another element (e.g., HNO3 = nitric acid).

Atomic Structure and Quantum Theory

Nature of Light

• Light exhibits wave-like properties, characterized by wavelength ($\lambda$), frequency ($\nu$), and amplitude.

• Relationship: $c = \lambda \nu$ where $c$ is the speed of light.

Energy of Light

• Energy of a photon: $E = h\nu = \frac{hc}{\lambda}$

• Planck's constant: $h = 6.626 \times 10^{-34} \text{ J s}$

Photoelectric Effect

• Electrons are ejected from a metal surface when exposed to light of sufficient frequency.

• Minimum energy required: $E = h\nu$

• Kinetic energy of emitted electrons: $KE = \frac{1}{2}mv^2 = h\nu - h\nu_0$

Atomic Spectra and the Bohr Model

Atomic Spectra

• Atoms emit light at specific wavelengths, producing line spectra.

• Hydrogen spectrum explained by Bohr's model.

Bohr Model of the Hydrogen Atom

• Electrons occupy stationary states (energy levels).

• Energy of electron in the nth orbit: $E_n = -R_H \frac{1}{n^2}$

• Transitions between energy levels result in absorption or emission of photons.

Quantum Mechanics

Wave-Particle Duality

• Louis de Broglie proposed that particles have wave-like properties: $\lambda = \frac{h}{mv}$

Heisenberg's Uncertainty Principle

• It is impossible to know both the position and momentum of a particle simultaneously: $\Delta x \cdot \Delta p \geq \frac{h}{4\pi}$

Wavefunctions

• The electron in an atom is described by a wavefunction ($\psi$), which gives the probability of finding the electron in a particular region of space.

Summary Table: Key Equations

Concept	Equation
Speed of light	$c = \lambda \nu$
Photon energy	$E = h\nu = \frac{hc}{\lambda}$
Bohr energy levels	$E_n = -R_H \frac{1}{n^2}$
de Broglie wavelength	$\lambda = \frac{h}{mv}$
Uncertainty principle	$\Delta x \cdot \Delta p \geq \frac{h}{4\pi}$

Example Problems

• Calculate the frequency of light with a wavelength of 650 nm: $\nu = \frac{c}{\lambda}$

• Calculate the energy of a photon with a wavelength of 450 nm: $E = \frac{hc}{\lambda}$

• Find the wavelength of a ball of mass 0.2 kg moving at 30 m/s: $\lambda = \frac{h}{mv}$

Additional info: These notes provide foundational concepts for understanding atomic structure, chemical bonding, and the quantum mechanical model of the atom, which are essential for further study in organic chemistry.