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

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" »

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" »

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" »

Chemical Bonding Fundamentals

Chemical bonding describes how atoms or ions join to form molecules, giant structures, or lattices.

The Octet Rule

Atoms that bond tend to gain, lose, or share electrons until they complete their valence shell with eight electrons.

Primary Types of Chemical Bonds

• Ionic Bonding

  Originates from the electrostatic forces between oppositely charged ions, resulting in the formation of an ionic crystal.

• Covalent Bonding

  Originates when atoms share electrons so that their valence shells are filled, thereby satisfying the octet rule.

Models and Theories of Bonding

• Lewis Model

  The bond is established when attractive forces between atoms are balanced by repulsive forces.

• Standard Electronic Clouds Model

  The charge density between the

Burette: Precision Volume Measurement

The burette is a **glass device** used to measure volumes with high accuracy. It consists of a graduated cylinder marked from top to bottom in cm³ (milliliters). Its primary advantage is allowing the precise dispensing of liquid drop by drop, controlled by a **stopcock** (key) located at the bottom. This stopcock regulates the flow, making it essential for titrations.

Volumetric Pipette (Bulb Pipette)

These are long glass tubes featuring an **enlargement (bulb)** in the central part. The lower section is finished sharply. Volumetric pipettes are designed to measure and transfer a single, fixed volume of liquid with high precision.

Graduated Pipette (Measuring Pipette)

Graduated pipettes are narrow glass tubes... Continue reading "Essential Laboratory Glassware and Tools: Function and Design" »

Key Lighting Terminology

Luminous Flux

The amount of light emitted by a light source, measured in lumens (lm).

Luminous Efficacy

The ratio of the luminous flux emitted (in lumens) to the power consumed (in watts). Its unit is lm/W.

Color Rendering Index (CRI)

Indicates the quality level of light sources in reproducing colors as accurately as possible.

Color Temperature (K)

Different light sources emit light at various color temperatures, measured in Kelvin (K). Here are some common examples:

• Incandescent Lamp: 2,800 K
• Fluorescent Lamp (Warm White): 3,000 K
• Fluorescent Tubes (Cool White): 4,000 K
• Fluorescent Tubes (Daylight): 6,000 K
• Direct Sunlight (Clear Sky): 6,000 K

Types of Electric Lamps

Electric lamps are categorized based on their operating principles:... Continue reading "Understanding Electric Lamps & Lighting Terminology" »

Ferrous Metals: Definition and Production

Ferrous materials, also known as steel products, are all those with iron as their main component. The primary types include cast iron (or pig iron) and steel.

Pure iron is weak and soft. To improve its properties, iron alloys are created by mixing iron with carbon. The amount of carbon added determines whether cast iron or steel is produced; cast iron has a higher carbon content.

Steel Manufacturing Process

Steel is typically obtained through a foundry process conducted in three main stages:

1. Concentration
2. Reduction
3. Refinement

The Reduction Stage

During the reduction stage, iron ore is introduced into a blast furnace along with coking coal and limestone.

• Coking coal serves as a fuel with high calorific value.
• Limestone

Material Properties in Metallurgy

Tenacity: Resistance to Impact and Fracture

Tenacity is the resistance to impact stress and fracture, or the ability of a metal to change shape without breaking. It requires both significant strength and plasticity.

Fragility: Lack of Plasticity

Fragility expresses a lack of plasticity and, consequently, tenacity. Brittle materials break within their elastic limit; that is, failure occurs spontaneously upon reviewing the load. In contrast, a material is considered tough if it possesses some capacity for expansion and breaks only after significant deformation.

Resilience: Shock Resistance

Resilience is a metal's resistance to breakage by shock. This property is often determined by the Charpy impact test.

Creep (Fluence)