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

Ranking Elements

The first classification of chemical elements was based on their chemical and physical properties, dividing them into two large groups: metals and non-metals.

• The first classification was done by J.W. Döbereiner. He observed a link between the atomic mass and properties of elements such as barium, calcium, and strontium. He arranged 40 elements in a line, one after another, by their mass.
• John Newlands arranged the elements by atomic mass, from the lowest to the highest, in columns. This is now called the Law of Octaves.
• D.I. Mendeleev arranged the elements by atomic mass. As a result of this work, the periodic law of elements was discovered in 1869.

Forces Between Molecules

These are listed from weakest to strongest:

1. Dispersion

Atomic Structure: Models and Definitions

The Plum Pudding Model

The Plum Pudding Model considers the atom as a ball of positive charge with electrons (negative charge) embedded.

The Rutherford Model

Rutherford's Bombardment Experiment

Rutherford tested the Rutherford Model by bombarding metal foil atoms with alpha particles (projectiles harder than atoms).

Experimental Results

• Result 1: The majority of alpha particles passed through the foil undeflected.
• Result 2: Some of these particles suffered deviation.
• Result 3: Very few rebounded and turned back.

Interpretation and Consequences

The interpretation was that particles that crossed the foil showed that atoms are not solid, but contain much empty space.

The Consequences of the Rutherford Atomic Model... Continue reading "Atomic Structure Fundamentals: Models, Particles, and Radioactivity" »

Reactions in Aqueous Solutions

Acid and Base Definition According to Bronsted-Lowry

Acid: A substance capable of donating protons.

Base: A substance capable of accepting protons.

For a substance to act as an acid, it must be in the presence of another substance that acts as a base and accepts the proton transferred by the acid. In aqueous solutions, water plays the role of both acid and base.

• When an acid donates protons, it becomes a species capable of accepting protons, called the conjugate base.
• When a base accepts protons, it is transformed into a species capable of donating protons, i.e., an acid, called the conjugate acid.

Equilibrium of Water Dissociation and the Concept of Kw

Water behaves as both an acid and a base according to the reaction:... Continue reading "Chemical Reactions in Aqueous Solutions and Stoichiometry" »

Atomic Structure Concepts

Balmer Series

The striped visible emission spectrum of H corresponds to the transitions of excited electrons returning to level n = 2.

Lyman Series

If electrons transition to level n = 1, the energy differences are greater, resulting in higher frequencies. The lines of this spectrum appear in the ultraviolet region.

Quantum Model and Orbitals

Quantum Model

An electron with a given energy sublevel occupies a defined region of space called an orbital.

Orbital Definition

An orbital is a region of space where there is a high probability of finding the electron.

Form of an Orbital

The form of an orbital depends on the type of sublevel (q) it belongs to. S orbitals are spherical; P orbitals are dumbbell-shaped (often described as '... Continue reading "Atomic Structure and Chemical Laws Explained" »

Concrete Terminology and Definitions

Mixing Water Definition

Mixing Water: Water contained in fresh concrete minus the water absorbed by the aggregate to reach the Saturated Surface Dry (SSD) condition.

Aggregates and Water Absorption

Aggregates (Rocks): Aggregates have pores, and when in contact with water, absorption occurs until they become saturated (often appearing shiny).

Water-Cement Ratio (W/C Ratio)

Water-Cement Ratio (W/C): The ratio between the mass of free water and the mass of cementitious materials (cement and additives).

Kneading (Mixing)

Kneading (Mixing): The process of combining the smaller fractions of concrete materials (the matrix) at one time.

Concrete Mechanical Resistance

Mechanical Resistance

Mechanical Resistance (Strength):... Continue reading "Concrete Terminology and Mechanical Resistance Testing" »

Part 1: Fundamentals of Electricity and Matter

What is Matter?

Matter is made up of elementary particles that form atoms.

The Structure of the Atom

The atom comprises a core (nucleus) and an outer shell (crust).

Electric Charge and Atomic Components

The atomic components are protons, neutrons, and electrons. The nucleus contains protons and neutrons, while the electrons reside in the outer shell.

• Neutrons: Are electrically neutral (do not carry a charge).
• Protons: Have a positive electric charge.
• Electrons: Have a negative electric charge.

Negatively Charged Atoms (Ions)

An atom becomes negatively charged when it possesses an excess of electrons.

Neutral Atoms and Charge Balance

An atom is electrically neutral when the number of protons (positive charges)... Continue reading "Atomic Structure, Electric Charge, and Material Conductivity" »

Chemical Bonding

Introduction

Chemical bonds are the forces that hold atoms together, leading to the formation of molecules and crystals. There are three primary types of chemical bonds:

1. Ionic Bonds

Ionic bonds occur between a metal and a nonmetal. In this type of bond, one atom loses electrons (forming a positive ion called a cation) while the other gains electrons (forming a negative ion called an anion).

2. Covalent Bonds

Covalent bonds form between two nonmetals. Atoms in a covalent bond share electrons to achieve a stable electron configuration. Each shared pair of electrons represents a covalent bond. These bonds can be visualized using Lewis diagrams.

3. Metallic Bonds

Metallic bonds occur between atoms of the same metal. In metallic bonding,... Continue reading "Understanding Chemical Bonds: A Comprehensive Look" »

Acid-Base Reactions

Acid-base reactions are essential in chemistry, allowing us to determine the concentration of an acid or base solution through titration. This process involves using a solution of known concentration (a standard solution) and an acid-base indicator.

Neutralization

Neutralization is the combination of hydrogen ions (H⁺) and hydroxide ions (OH^-) to form water (H₂O) and a salt. These reactions are exothermic, meaning they release heat.

Acid + Base → Salt + Water

Titration of a Strong Acid with a Strong Base

When titrating a strong acid (e.g., hydrochloric acid, HCl) with a strong base (e.g., sodium hydroxide, NaOH), the reaction is a straightforward neutralization:

HCl + NaOH → NaCl + H₂O

Titration of a Weak Acid with a Weak Base

Titrating... Continue reading "Acid-Base Reactions: Titration, Neutralization, and Indicators" »

Supercomputers

Powerful machines using processors similar to those in PCs, connected together and typically engaged in complex scientific applications, such as:

• Understanding biological processes
• Climate modeling
• Studying physical phenomena like particle collisions

Classification is often based on a benchmark test involving solving a system of equations. This can be considered unfair as not all supercomputers are designed for this specific task, though many are intended for numerical calculations. They utilize thousands of processors working in parallel to analyze problems. The optimal process varies depending on the problem, the communication needs between processors, and system optimization strategies to maximize speed.

Fullerenes

A fullerene is... Continue reading "Advanced Materials and Computing Concepts" »

1) Solution

A homogeneous mixture of two or more substances formed by a solute dispersed in a solvent.

2) Tyndall Effect

Visual of a light beam passing through a homogeneous mixture.

3) Concentration

The relationship between the amount of solute and solvent.

4) Dissolution

The process of scattering solute particles within the solvent.

5) Solubility

Expresses the maximum amount of solute that can dissolve in a given solvent.

6) Polar Molecule

A molecule with an uneven distribution of electronic charge along its structure.

7) Non-Polar Molecule

A molecule with a uniform distribution of electronic charges.

8) Types of Concentrations

• Dilute: A solution containing a small amount of solute.
• Saturated Solution: Contains the maximum amount of solute at a given temperature.