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

Atomic Structure Fundamentals

What Are Electrons?

Electrons are negatively charged particles found in all atoms and charged particles.

Thomson's Atomic Model

According to Thomson, the atom was a mass of positive charge with embedded electrons. The negatively charged electrons were distributed within this positive charge to ensure the atom was neutral.

Rutherford's Atomic Model

In Rutherford's model, the atom is formed by a very small nucleus and an electron cloud (cortex). In the nucleus, all its positive charge and almost all its mass are concentrated. In the electron cloud, electrons orbit the nucleus.

Bohr's Atomic Model

The Danish scientist Niels Bohr conducted a series of studies and concluded that electrons orbit the nucleus in specific, quantized... Continue reading "Atomic Structure & Periodic Table: Essential Chemistry Concepts" »

What is Matter?

Matter is anything that occupies space and has mass. This includes land, water, air, and more. Essentially, if something exists physically, it is considered matter.

Theories of Matter

Historically, there were two main theories regarding the divisibility of matter:

• Matter is discontinuous: This theory proposed that there is a fundamental, indivisible unit of matter. This smallest unit was called an "atom."
• Matter is continuous: This theory suggested that matter could be infinitely divided into smaller and smaller parts.

It was eventually proven that matter is discontinuous, meaning atoms exist.

Thompson's Atomic Model

J.J. Thompson's model, often called the "plum pudding" model, depicted the atom as a sphere of positive charge with negatively... Continue reading "Understanding Matter: Atoms, Structure, and Properties" »

Volumetric Analysis

Requirements for Volumetric Reactions

For a reaction to be used in volumetric analysis, it must meet the following criteria:

• The reaction between the titrant and the titrated substance must be quantitative, without adding excess reagent. The reaction must be complete at the equivalence point.
• The reaction must be fast. If it is slow, it is possible to accelerate it with temperature or catalysts.
• The reaction must be stoichiometric and definite.
• To determine the endpoint, a sensitive method must be available.

Characteristics of a Standard Solution

To prepare a standard solution, there are two methods:

1. Directly dissolve a standard substance and dilute to an exact volume (using a volumetric flask).
2. Prepare a solution of approximate concentration

Tin: Metallurgy, Properties, and Applications

Pyrometallurgical Reduction of Cassiterite

Cassiterite is processed in a reverberatory furnace where tin is reduced by raw coke and subsequently refined.

Electrolytic Recovery of Tin

This process involves inserting crude tin into a sodium hydroxide solution, which dissolves the tin. The metal is then obtained by electrolysis of the solution.

Applications of Tin

Pure tin is used to form alloys such as bronze, and in applications like metal welding, metal printing, antifriction alloys, and low melting point alloys.

Lead: Characteristics, Metallurgy, and Refining

Properties of Lead

Lead is a bluish-gray metal, known for being heavy and soft.

Metallurgy of Lead

Galena is often used as the starting material. Rich... Continue reading "Tin, Lead, Zinc, Aluminum: Metallurgy, Properties, and Uses" »

Scientific Prefixes and Submultiples

Understanding scientific prefixes is crucial for expressing very large or very small numbers concisely. Here are common prefixes and their factors:

• Giga (G): 10⁹
• Mega (M): 10⁶
• Micro (µ): 10^-6
• Nano (n): 10^-9
• Pico (p): 10^-12

Understanding Scientific Notation

Scientific notation is a way of writing numbers that are too large or too small to be conveniently written in decimal form. It is commonly used in science, where it is also called "standard form" or "standard index form."

Example: To express 38,000 meters with three significant figures:

38,000 m = 3.80 x 10⁴ m

Gas Volume Variation at Constant Pressure (Charles's Law)

When the temperature of a given mass of gas increases, if the pressure remains constant, the volume... Continue reading "States of Matter and Gas Laws Explained" »

Understanding Key Organic Functional Groups

Phenols: Structure and Naming

Phenols are aromatic derivatives characterized by the presence of a hydroxyl (-OH) group directly attached to an aromatic ring. They exhibit acidic properties and can form metal salts.

These compounds are widely distributed in natural products, such as tannins.

Naming Conventions for Phenols

Phenols are named similarly to alcohols, with the suffix "-ol" appended to the name of the parent hydrocarbon when the -OH group is the principal functional group. For example, benzene with an -OH group is named phenol.

When the -OH group is not the principal functional group, the prefix "hydroxy-" is used, followed by the name of the hydrocarbon.

If the benzene ring has several substituents... Continue reading "Essential Organic Functional Groups: Phenols, Aldehydes, Ethers, Ketones" »

Introduction to Materials Science

Materials Science is an extensive discipline that relates the structure, properties, and application of engineering materials.

What are Engineering Materials?

Engineering materials are defined as those materials that, due to their desirable properties, can be used in machinery parts, structural elements, or for other engineering purposes. These materials can be structurally crystalline or amorphous and include:

• Metals
• Polymers
• Ceramics
• Composites (composed of two or more different materials from the families above)

Types of Engineering Materials

Metallic Materials

Metallic materials are substances whose atoms are joined by metallic bonds. These unique chemical bonds permit some atomic mobility and complete mobility for... Continue reading "Fundamentals of Materials Science and Engineering" »

Quantum Numbers

By solving the equations of quantum mechanics for an atom, quantum numbers appear as a mathematical consequence. These describe the behavior of electrons in the atom.

• The principal quantum number, n: Represents an energy level. It can assume any positive integer (1, 2, ...). The first level is the lowest energy, and subsequent levels, increasingly distant from the nucleus, have greater energies.
• The orbital angular momentum quantum number, l: Determines the orbital shape and energy within each level. It takes values between 0 and n-1 inclusive.
• The magnetic quantum number, m_l: Describes the orientation of the orbital in space. Among other things, it explains the splitting of spectral lines when an external magnetic field is applied.

What is a Mixture?

A mixture is a substance formed by combining two or more substances without a chemical reaction occurring that changes its components.

• A homogeneous mixture is one in which no substance loses its original properties and can be separated by physical means. It has a uniform composition throughout.
• A heterogeneous mixture is one that has a non-uniform composition in which components can be distinguished by the naked eye and consists of two or more physically distinct substances, unevenly distributed.

Physical Separation Techniques

Distillation

Distillation is used to separate two liquids with different boiling points by heating and subsequent condensation of the substances. The distillation process consists of two phases: first, the... Continue reading "Understanding Mixtures and Separation Techniques" »