Notes, summaries, assignments, exams, and problems for Chemistry

Fundamentals of Electricity

Etymology and Early Observations

Electricity originates from the Greek word "elelctron," meaning "amber." This name was given because the Greeks observed that fossil resin used in jewelry, when rubbed, attracted light objects.

Thales' Discovery

Thales noted that when amber was rubbed with force using cloth, silk, wool, or skin, it would attract light materials.

William Gilbert's Contribution

William Gilbert observed that this attractive behavior was not limited to amber and similar substances. He recognized these phenomena as electrostatics.

Causes and Natural Phenomena

These electrostatic phenomena are caused by the behavior of atoms in each material. Natural phenomena associated with electricity include:

• Lightning storms.

Understanding Atoms: Key Concepts

Atom: The smallest unit of a chemical element that retains its identity and properties, and cannot be split by chemical processes.

Mass Number: Represents the sum of protons and neutrons present in the atomic nucleus. Also known as the nucleon number.

Atomic Number: The positive integer that equals the total number of protons in an atom's nucleus.

Ion: A particle formed when a neutral atom or group of atoms gains or loses one or more electrons.

Cation: An ion (either atom or molecule) with a positive electric charge.

Anion: An ion (either atom or molecule) with a negative electric charge.

Isotope: Used to indicate that all isotopes of the same element are found in the same place in the periodic table.

Atomic Mass:... Continue reading "Understanding Atoms: Mass, Number, Ions, and Isotopes" »

Atomic Structure and Quantum Concepts

Notation: Z (Atomic Number) = Protons; A (Mass Number) = Protons + Neutrons.

• Cation: Positive charge, loses electrons.
• Anion: Negative charge, gains electrons.

Radiation and Energy Calculations

Frequency: f = c / λ (where c = 3 × 10⁸ m/s).

Planck's Constant: E = h × f (h = 6.63 × 10^-34 J·s).

Energy Levels: ΔE = E_f - E_i = -K / n².

• Absorption: Inf → Sup (Energy +).
• Emission: Sup → Inf (Energy -).

Isotopes and Quantum Numbers

Isotopes: Same atomic number (Z) but different atomic mass (A).

• n (Principal): Energy level (1, 2, 3...).
• l (Angular Momentum): Orbital shape (0 to n-1).
• m_l (Magnetic): Orientation (-l to +l).
• m_s (Spin): Electron spin (+½, -½).

Orbital Types

• l = 0: s²
• l = 1: p⁶
• l = 2: d¹⁰
• l = 3: f¹⁴

Electron Configuration

Möller

States of Matter and Their Changes

State changes are processes experienced by the body according to the environmental conditions of pressure and temperature.

• Solid-Liquid (Fusion)
• Liquid-Gas (Vaporization)
• Gas-Solid (Deposition)
• Liquid-Solid (Solidification)
• Solid-Gas (Sublimation)
• Gas-Liquid (Condensation)

When heating a body, the energy of the particles increases. There comes a moment when this energy is sufficient to overcome the forces of cohesion, and then fusion occurs when we consider that part of a solid body. The same applies to all states of aggregation. The form of fusion of a body depends on its nature. We will distinguish between crystalline and amorphous bodies.

• In a crystalline body, such as ice, melting is produced at a constant temperature

Chemical Elements

These are the fundamental building blocks from which all matter is composed.

Chemicals

This is a substance that cannot be separated into its components by physical processes.

Alloys

Artificial mixtures made from two or more chemical elements or compounds.

Composites

Composite materials made from two or more components that have very different physical and chemical properties, and which together form a substance with properties different from those of its separate components.

Metal Extraction System

Metals are obtained basically by two industrial processes: heat or electricity. In both processes, this is done via a chemical reaction called reduction, in which the pure metal is obtained by separating it from the compound where it is... Continue reading "Key Concepts in Materials and Nanotechnology" »

Ammonia

Ammonia is a colorless gas with a characteristic, suffocating odor. It is prepared from hydrogen and nitrogen using the method introduced by Haber and Bosch in Germany, known as the Haber synthesis. The stages of this method are:

• Preparation of synthesis gas: Processes to obtain the hydrogen and nitrogen needed for the reaction.
• Catalytic synthesis: The gases are contacted with a catalyst in a reactor at temperatures ranging from 400 to 600 °C and pressures from 200 to 1000 atm.
• Separation of ammonia: The mixture from the reactor is cooled until the ammonia liquefies and separates from the gas stream; the remaining nitrogen and hydrogen are recycled.

Ammonia is used as a cleaning agent due to its great solvent power, as a refrigerant in... Continue reading "Industrial Chemical Processes and Material Properties" »

General Properties of Metals

• Electrical and thermal conductivity: Excellent conductors of heat and electricity.
• Resistance: Resistant to stress and efforts.
• Mechanical properties: High toughness, ductility, and malleability.
• Physical state: Solid at room temperature (except for mercury).
• Economic factors: Generally economical and heavy.
• Magnetism: Some exhibit magnetic properties.
• Melting point: High fusion temperatures.

Classification of Metals

Most metals are not used in their pure form but as alloys. They are classified into ferrous and non-ferrous metals.

Ferrous Metals and Alloys

• Soft Iron: Considered pure iron; it is silver in color but oxidizes easily and can crack internally.
• Steel: Ductile and malleable; it oxidizes easily but can be forged and

Kinetic Model of Gases: Microscopic Behavior

For centuries, scientists sought a model to explain the behavior of gases at the microscopic level. The simplest model assumes that a gas consists mainly of empty space occupied by small particles in constant, chaotic motion. This model is called the Corpuscular Kinetic Model.

Key Characteristics of Gases

• When heated, gas temperature increases.
• Gases exert pressure.
• Gases tend to fill the entire volume available.
• A larger volume may result in less pressure (at constant temperature).
• Higher volume and higher temperature are related.
• At higher temperatures, gases diffuse more rapidly.

The Kinetic Theory of Matter

Matter consists of very small particles that cannot be seen. These particles are in continuous,... Continue reading "Kinetic Theory of Matter: States, Properties, and Systems" »

Dalton's theory, which posited atoms as indivisible particles, was eventually superseded by experiments revealing the electrical properties of matter. These groundbreaking studies demonstrated that atoms themselves contain smaller, subatomic particles responsible for electrical behavior: the electrons.

Early Atomic Theories and Electron Discovery

Thomson and the Electron

Towards the end of the 19th century, J.J. Thomson conducted groundbreaking experiments using cathode ray tubes (discharge tubes with a positive and a negative pole across which an electric current passed). He discovered a negatively charged particle within the atoms of chemical elements, which he named the electron. When an electrical discharge occurred between the plates, a beam... Continue reading "Atomic Structure Explained: Subatomic Particles & Key Models" »

Fundamental Chemistry Definitions

• Solute: Substance dissolved in a dispersing phase.
• Saturated Solution: Contains the maximum quantity of solute that can be dissolved.
• Solution: A homogeneous mixture.
• Solvent: The medium in which the solute is dispersed.
• Homogeneous Mixture: Maintains constant concentration throughout.
• Heterogeneous Mixture: Varies in the amount of components throughout.

Concentration and Measurement Units

• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kilogram of solvent.
• Density: Mass per unit of volume.
• Molar Mass: The sum of atomic masses of a substance (grams per mole).
• Moles: The ratio between mass and molar mass.
• % w/w (Mass/Mass): Grams of solute in 100 grams of solution.
• % m/v (Mass/Volume)