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

Modelos atómicos: Thomson, Rutherford y Bohr

Thomson imaginó el átomo como una especie de área continua positiva en la que los electrones están incrustados, más o menos como pasas en un pudding. Este modelo de Thomson fue bastante razonable y fue aceptado durante varios años, ya que permitía explicar ciertos fenómenos.

Formación de iones

La explicación de la formación de iones es la siguiente: un átomo que ha ganado o perdido uno o más electrones se convierte en un ion. Los electrones pueden perderse o ganarse con relativa facilidad, de modo que su número puede variar dentro del átomo, mientras que el número de protones se mantiene siempre fijo para cada átomo.

Un átomo que pierde electrones se convierte en un ion positivo o... Continue reading "Evolution of Atomic Models: Thomson to Bohr" »

Fundamental Chemical Definitions

Molecule

The union of atoms.

Lattice

A continuous structure of millions of atoms.

Chemical Bond

The attractive force that keeps atoms united in a molecule or a crystal.

Elementary Chemical Substance

Atoms of the same element that unite.

Chemical Compound

Atoms of different elements that unite.

The Octet Rule

Atoms of different chemical elements tend to join with other atoms to have eight electrons in their outermost shell, known as an octet, to achieve greater stability.

Types of Chemical Bonds

Ionic Bond

The transfer of valence electrons. The ionic bond is the union of oppositely charged ions through electrostatic forces of attraction. In this case, the elements bond to achieve a noble gas electron configuration.

Ionic Crystal

A... Continue reading "Chemical Bonding and Material Attributes" »

Tissue Homogenization and Protein Extraction

Tissues are rich in proteins that fulfill different functions and therefore possess different characteristics. Depending on these traits, it is possible to solubilize, separate, and purify them through various methods.

Methods for Cell Disruption

The first step in the extraction of most proteins and subcellular structures is the disruption of tissues or cells to obtain a cell lysate. In this lysate, the protein or multiprotein complex subcellular structure is kept in conditions that permit isolation. This is accomplished using procedures commonly known as soft mechanical homogenization.

These methods produce the rupture of cell membranes gently, thereby releasing the cellular contents. Common techniques... Continue reading "Protein Extraction and Bradford Assay Quantification" »

Substances, Mixtures, and Separation Techniques

1. Pure Substances vs. Mixtures

• Distilled Water: Pure substance/compound
• Tap Water: Mixture/homogeneous
• Diamond: Pure substance/element
• Gasoline: Mixture/homogeneous
• Wine: Mixture/homogeneous
• Air: Mixture/homogeneous

2. Dalton's Theory

• Matter is made up of indivisible and indestructible atoms.
• All atoms of the same element are equal in mass and properties.
• Compounds are formed by the combination of different elements.

3. Separation Techniques

• Screening: Separates solid particles of different sizes. Instrument: sieve.
• Filtration: Separates solids from liquids. Instrument: filter.
• Evaporation: Separates solids from liquids when the liquid is not needed. Works best with homogeneous mixtures. The process is faster

Errors of Measurement

Large errors are due more often, even when incorrect sampling is applied, or an application of the method is not suitable. The most likely causes of errors are:

1. Material is strategically in the form $k$ is done, but does not take into account the disposition of strata; i.e., $k$ is not proportionately represented.
2. Analytical property $k$ is measured, which varies non-uniformly from the surface to the center.
3. $k$ in suspension during transport; there is a separation of particles, making it impossible to shake the entire volume for a homogeneous sample.

Preparation of Materials

Reagent Concentrations:

• Aqueous reagents: Physical concentration (% P, % V).
• Aqueous reagents: Chemical concentration (M, N, m).

Treatment of the Sample

Before... Continue reading "Mastering Analytical Chemistry: Error Sources and Sample Preparation" »

Aluminum

Aluminum is used in telescopes. Tempered powder paint is used in metal protection and the preparation of alloys. Aluminum forms alloys with other metals. Duralumin, an aluminum alloy, is used in aeronautics because it is very lightweight and has great resistance.

Aluminothermy

Aluminothermy is a metal extraction procedure that reduces metal oxides using aluminum powder. Metals such as chromium, manganese, and molybdenum are obtained using this method.

Salts of Aluminum

Important industrial salts are called alum (double salts).

Natural Aluminum

Aluminum is not found free in the Earth's crust. It is named after these characteristics:

1. Alumina
2. Hydroxide
3. Silicates

Obtaining Aluminum

Aluminum is extracted using the electrolytic method. Bauxite and cryolite... Continue reading "Aluminum, Copper, Polymers, and Ceramics: Properties and Uses" »

Fuel Properties and Combustion

Oil is formed by the decomposition of organic matter, primarily plankton, in marine environments. It contains the remains of animals and is a mineral found in sedimentary rock formations.

Soluble compounds begin to form, undergoing thermal decomposition into hydrocarbons (HC).

Gaseous Fuels

Gaseous fuels, also called hydrocarbons (HC), are designed for use in combustion. They are divided into natural gas fuels and manufactured gaseous fuels.

Advantages and Properties of Gaseous Fuels

The calorific value varies greatly depending on the type of gas and the presence of non-combustible components. Non-combustible components lower the heat efficiency of combustion.

Calorific value is the heat released during combustion.

Specific

States of Matter

Solid State

Solids are characterized by molecules that are tightly packed with minimal empty spaces. They possess a defined shape and volume and do not flow. Examples include: aluminum, diamond, gold, salt, sugar, flour, and cups.

Liquid State

Liquids consist of molecules with disordered empty spaces, allowing them to flow and adopt the shape of their container. They have a defined volume but no definite shape. Examples include: ethanol, milk, oil, paraffin, water, juice, and cologne.

Gaseous State

Gases have no definite form or volume, adopting the shape and volume of their container. Their molecules are extremely separated and spread rapidly. Examples include: chlorine, nitrogen, Tanax (insecticide), Lucu gas, spray paint, and... Continue reading "Matter, Minerals, and Modern Materials: Core Concepts" »

The Nature of Matter and Its Changes

Chemistry is the scientific discipline dedicated to studying the nature of matter and the changes affecting its composition and properties.

Physical vs. Chemical Changes

• Physical changes do not alter the fundamental nature or chemical identity of substances. Examples include melting ice or boiling water.
• Chemical changes (or chemical reactions) result in the formation of new substances with different chemical properties. Examples include burning wood or rusting iron.

Classifying Matter

Pure Substances

A pure substance has a definite and constant composition, characteristic physical and chemical properties, and cannot be separated into other substances through physical methods.

Mixtures

A mixture has a variable composition... Continue reading "Chemical Principles: Understanding Matter and Its Transformations" »

Chemical Bonding and Atomic Properties

1) In the compound NaCl:
I. A pair of atoms share their electronic link (F)
II. Sodium presents the electronic configuration of Neon (V)
III. Chlorine presents the electronic configuration of Argon (V)

2) In the compound MgCl₂, we can say that magnesium:
I. Has an octet in its valence shell (V)
II. Lost 2 electrons (V)
III. Gained 2 electrons (F)
IV. Shares its valence electrons (F)

4) Given the compounds PCl₅, BF₃, CH₄, and XeF₄, it is possible to say:
I. Carbon (C) satisfies the octet rule (V)
II. The compound BF₃ has 26 total valence electrons (F)
III. P and Xe have 5 and 8 valence electrons, respectively (V)

Stoichiometry and Chemical Reactions

6) One of the main reactions in the metallurgy of Iron (Fe)