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

Key Discoveries in Atomic Theory

Thomson's Discovery of Electrons

J.J. Thomson demonstrated that atoms contain tiny, negatively charged particles called electrons. He showed that atoms could lose electrons, suggesting a static atomic model.

Rutherford's Atomic Model

Ernest Rutherford established that atoms are mostly empty space. He proposed that a small, dense region, which he named the nucleus, resides at the atom's center. This nucleus contains protons and, as Rutherford suspected, neutrons. In his model, the number of protons equals the number of electrons, with the latter orbiting the nucleus in circular paths.

The Atom as a Planetary System

The Rutherford model is analogous to a planetary system because the nucleus represents the sun, and the... Continue reading "Atomic Structure and the Periodic Table" »

Biological Molecules and Biomolecules

Inorganic: H₂O, O₂, CO

Organic (Macromolecules): Proteins, Nucleic Acids, Carbohydrates, Lipids

Structure and Function of Macromolecules

• Polysaccharides: Polymers with structural functions (cellulose) or energy storage (glycogen).
• Nucleic Acids: Polymers of 4 nucleotides. Function associated with the storage, transmission, and expression of genetic information.
• Proteins: Combinations of 20 amino acids. Different functions (catalytic, structural, transport, hormones, antibodies, receptors).
• Lipids: Do not polymerize, they associate. Structural or functional roles.

Characteristics of Living Matter

Living things are made of chemical molecules interacting in an aqueous fluid, acquiring new physicochemical properties... Continue reading "Biomolecules and the Role of Water in Living Matter" »

The Krebs Cycle

The Krebs cycle, also known as the Citric Acid Cycle, is an amphibolic pathway because:

• It facilitates the degradation of Acetyl-CoA.
• Its intermediate compounds serve as precursors for other synthetic processes.

Stages of the Krebs Cycle

The cycle is divided into the following stages:

1. Formation of Citric Acid

   Citric acid is formed from oxaloacetic acid and Acetyl-CoA.

   • Modifications: Oxaloacetic acid + Acetyl-CoA → Citric acid
   • Inputs/Outputs: Enters H₂O and Acetyl-CoA

2. Isomerization of Citric Acid to Isocitric Acid

   • Modifications: Citric acid → Isocitric acid
   • Inputs/Outputs: None

3. Oxidation of Isocitric Acid

   Isocitric acid is oxidized, reducing NAD⁺ to NADH, forming alpha-ketoglutarate, and releasing CO₂.

   • Modifications: Isocitric acid →

Defrosting is essential in refrigeration systems to remove ice accumulation on evaporators, which reduces efficiency and cooling capacity.

Natural Defrosting

This method is typically used in refrigerated spaces operating above +2°C. It involves stopping the refrigeration system (compressor and fans) for a period, allowing the warmer ambient air within the refrigerated space to melt the ice accumulated on the evaporator.

In low-temperature facilities for freezing and storage of frozen products, based on forced-air evaporators, it becomes necessary to create additional heat for defrosting to melt the ice.

Water Spray Defrosting

This method involves spraying water under pressure onto the ice accumulated on the evaporator. The water melts the ice and... Continue reading "Refrigeration Defrost Methods" »

Chemical Substances and Mixtures

Chemical substances: N-type material: characteristic properties defined by Cunhas.

Mixtures (Mestura Kimicar)

Mixture: Contains two or more components; often called a chemical mixture (mestura kimicar).

• Heterogeneous (straight): Two or more phases present.
• Homogeneous (homo): One phase present (solution).

Colloidal Dispersions

Colloidal dispersion: A type of heterogeneous mixture in which the phases are not easily distinguished by the microscope. It has two main parts:

• Dispersed phase: The component present in lesser proportion; it is discontinuous and appears as separate particles.
• Dispersing (continuous) phase: The component present in greater proportion; it constitutes the continuous medium.

Solubility

Solubility: The... Continue reading "Properties and Separation Methods of Chemical Substances" »

Hemoglobin Iron Environment and Geometry

The iron ion (Fe) in Hemoglobin (Hb) is in a square planar environment, bonded to four nitrogen (N) atoms of the porphyrin ring. The fifth coordination position is bound to a nitrogen atom from a histidine residue (perpendicular to the plane), and the sixth position binds O₂ in oxyhemoglobin. When oxygenated, the coordination geometry around the iron is essentially octahedral. In contrast, deoxygenated Hb has a five-coordinate, square pyramidal geometry, as the sixth position is vacant.

Role of Magnesium and Calcium Competition

Magnesium (Mg) is extremely important. It plays a role related to the Na⁺/K⁺ pump; the interior of the cell requires large amounts of K⁺ and low amounts of Na⁺. Mg facilitates the... Continue reading "Iron and Copper Roles in Biological Oxygen Transport" »

The Molecular Structure of Water

Water exhibits a unique physical behavior because the two electrons shared in the molecule (from two hydrogen atoms) are unevenly shared, shifting toward the oxygen atom. This creates a negative pole at the oxygen atom and two positive poles where the hydrogen atoms are located. Therefore, water is fundamentally a bipolar molecule.

Key Physicochemical Properties of Water

Water possesses several critical properties:

1. High Cohesive Force: Strong attraction between molecules due to hydrogen bonds.
2. High Adhesion Strength: Water molecules have a great capacity to adhere to the walls of small-diameter tubes, allowing them to climb against gravity (a phenomenon known as capillarity).
3. High Surface Tension: Its surface resists

Redox Reactions

Oxidation: A process in which an atom, ion, or molecule loses electrons.
Reduction: A process in which an atom, ion, or molecule gains electrons.

An oxidizing agent is a substance that gains the electrons lost during oxidation. A reducing agent is a substance that donates electrons, which are then gained during reduction. In short, a reducer is an electron donor, and an oxidant is an electron acceptor. Every redox reaction must involve at least one oxidizer and one reducer.

Balancing Redox Equations

Historically, oxidation was defined as the gain of oxygen. For example, in the reaction CO + 1/2O₂ → CO₂, carbon monoxide acts as the reducer, and the process is oxidation. Today, we follow the electron-transfer concept, and reactions... Continue reading "Redox Reactions: Principles, Volumetry, and Applications" »

Fundamental Atomic Structure

• Atom: The smallest unit of a substance that retains its chemical properties, composed of subatomic particles common to all elements.
• Atomic Number (Z): The number of protons in an atom's nucleus. In a neutral atom, this equals the number of electrons.
• Mass Number (A): The total number of particles in the nucleus (protons + neutrons).
• Isotopes: Varieties of the same element with the same atomic number (Z) but a different number of neutrons, resulting in a different mass number (A).

Chemical Quantities and Formulas

• Mole (mol): The amount of substance containing 6.022 × 10²³ particles, known as Avogadro's number.
• Empirical Formula: Indicates the simplest whole-number ratio of atoms in a molecule.
• Molecular Formula: Indicates

Atoms, Molecules, and Ions

Atoms: Electrically balanced particles consisting of one positively charged center called the nucleus, surrounded by a cloud of negatively charged particles called electrons, which exactly balance the nuclear charge.

Molecules: Electrically balanced particles with more than one positive center (nuclei). Molecules are sets of bonded atoms that act as a unit.

Ions: Atoms (or groups of atoms) with unbalanced charges.

The number of protons determines the number of electrons necessary to balance the atom's charge. Neutrons are the cementing material in the nucleus. The force between protons and neutrons is called the strong nuclear interaction. Number of protons = ATOMIC NUMBER of the atom (Z)

The atomic number is also given... Continue reading "Understanding Atoms, Molecules, and Ions: Structure and Properties" »