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

Understanding Chemical Bonds

Ionic Bond: This bond occurs when metallic elements interact with non-metal atoms. In this case, the metal atoms donate electrons to the non-metal atoms, becoming positively and negatively charged ions, respectively. These oppositely charged ions are attracted by strong electrical forces, being tightly bound and giving rise to an ionic compound. These electrical forces are called ionic bonds.

Covalent Bond: Covalent bonds are the forces that hold non-metallic atoms together. These atoms have many electrons in their outermost level (valence electrons) and tend to gain electrons rather than transfer them to acquire the stability of the electronic structure of a noble gas. Therefore, electrons from non-metallic atoms... Continue reading "Understanding Chemical Bonds: Ionic, Covalent, and Metallic" »

Understanding Atomic Structure and Models

What is a Subatomic Particle?

A subatomic particle is a particle smaller than an atom. It can be an elementary particle or a composite particle, in turn, composed of other subatomic particles such as quarks, which make up protons and neutrons.

Dalton's Atomic Theory: Foundations of Chemistry

Key Postulates of Dalton's Theory

1. Elements are composed of tiny particles called atoms.
2. All atoms of a given element are identical in mass and properties.
3. Atoms of one element differ from those of any other element; atoms of different elements can be distinguished by their relative atomic weights.
4. Atoms of one element combine with atoms of other elements to form chemical compounds. A given compound always has the same relative

Understanding Energy and Its Sources

What Is Energy?

Energy is the ability to perform work. Heat transfer is the process of energy spreading to an object. It occurs through several mechanisms:

• Convection: The circulation of fluids or gases.
• Radiation: The propagation of heat in the form of waves.

Forms of Energy

• Chemical Energy: Stored in the bonds of atoms.
• Electrical Energy: The energy that provides electricity.
• Nuclear Energy: The energy that holds particles together in an atom's nucleus.
• Radiant Energy: Carried by electromagnetic waves.
• Sound Energy: The energy produced by the displacement of waves.
• Kinetic Energy: The energy of motion.

Primary Energy Sources

Energy sources are natural resources from which we can obtain energy to produce heat, light,... Continue reading "Fundamentals of Energy: From Fossil Fuels to Nuclear Reactions" »

Vacuum electronics utilize various types of transducers for pressure measurement. These include bellows mechanical transducers, diaphragm transducers, thermal transducers, and ionization transducers.

Bellows and Diaphragm Transducers

Bellows and diaphragm transducers operate based on the pressure differential between atmospheric pressure and the process being measured. They can be offset relative to atmospheric pressure and calibrated in absolute units. These transducers are suitable for measuring high vacuum. They may be attached to strain gauges or capacitive elements for electrical output.

Thermal Transducers

Thermal transducers are based on the principle of proportionality between the energy dissipated from the hot surface of a filament heated... Continue reading "Vacuum Electronics: Bellows, Thermal, and Ionization Transducers" »

Classification of Substances

Substances can be classified according to different criteria:

• Natural and Artificial Substances

  Natural substances are those that exist in nature. Artificial substances are those formed from natural substances by chemical processes (man-made).

• Homogeneous and Heterogeneous Mixtures

  If we observe a substance that consists of several components and perceive distinct parts, we call it heterogeneous. Conversely, if we do not perceive a mixture, it is a homogeneous substance.

• Pure Substances and Mixtures

  Matter that contains a single substance is called a pure substance. Conversely, if it is formed by more than one substance, we call it a mixture.

• Solid, Liquid, and Gas States

  This is the best-known classification, made according

1. Origin of Fire

1.1. The Fire Tetrahedron

For a fire to occur, a chemical reaction between a fuel and an oxidizer is necessary, along with an activation energy. These three factors make up the fire triangle. The fire tetrahedron is formed by adding the chain reaction, which is a reaction that does not need external energy to be maintained.

• Fuel: A substance that reacts easily with an oxidizer to produce heat.
• Oxidizer: A substance that activates the fuel (e.g., oxygen).
• Activation Energy: The minimum energy required to initiate the combustion process.
• Chain Reaction: A self-sustaining reaction that does not require external energy.

Types of Fire

• Class A: Solid fuels like wood.
• Class B: Liquid or gas fuels like oil or acetylene.
• Class C: Electrical

Reinforcement Bars and Wires

Reinforcement bars and wire sizes (in mm):

• Bars (Corrugated, Smooth, and 40 Soldiers): 6, 8, 10, 12, 14, 16, 20, 25, 32.
• Wires (Smooth, used only for joists): 5, 6, 7, 8, 9, 10, and 12.

Material Properties and Identification

Key properties include: B lim elast. (Elastic Limit), Weldability, and Ductility. Features for identification include ovalization, the corrugation material identification, and country of origin.

Electrically Welded Mesh and High-Strength Steels

Electrically Welded Mesh (ME): Used for savings and separation (longitudinal x transverse). Identification includes: dl-disc (discontinuous longitudinal), BNS (bar), T (wire), b (width), xl (length), and electron beam processing (AB haltura c (step)).

The longitudinal... Continue reading "Steel Reinforcement, Welding Standards, and Material Quality Control" »

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