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

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" »

Conventional Thermal Power Plant Operation

Electric power is generated from the heat produced by the combustion of coal or natural gas fuel.

Core Components of the Thermoelectric Cycle

There are many types of boilers. The most commonly used are radiation boilers, so named because the heat energy is primarily transmitted by radiation.

Boiler Structure and Function

Boilers have a burner appropriate for the type of fuel used and a combustion chamber surrounded by innumerable tubes through which water circulates to vaporize.

Reheaters

Reheaters are parts of the boiler designed to eliminate water droplets accompanying the steam to convert it into dry steam.

Economizers and Preheaters

Economizers and preheaters harness the residual heat of the emitted combustion... Continue reading "Thermal Power Generation Plant Components and Cycle" »

Elements and Compounds

Elements are substances consisting of a single type of atom. Compounds are substances obtained by the grouping of atoms of different elements.

A Little History

Chemical Elements for Life: Bioelements

Bioelements are the chemical elements of living beings. The most abundant species are: C, H, O, N, Ca, P, Mg, S, Na, K, and Cl, and they make up more than 99% of these living things.

Trace Elements

Trace elements are present in lower proportions (approximately 0.1%) and are indispensable for all living things, such as Fe, Zn, Mn, F, I, Cu, and Co.

The RDA (Recommended Dietary Allowance) is the amount of nutrient that a healthy person should eat each day on average, as part of the diet, to maintain good health.

Isolated Atoms

The elements... Continue reading "Fundamental Chemical Substances and Structures" »

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 and Matter Fundamentals

Octet Rule

The formation of compounds tends toward atoms gaining electrons to achieve 8 electrons in their outermost shell.

Molecules

Molecules are formed by a set of atoms. Generally, small molecules are called diatomic (having 2 atoms), or triatomic, etc. Molecules are formed by atoms of the same element or consist of different atoms.

Crystals (General Structure)

Crystals are formed by a variable number of atoms, ions, or molecules, usually large, arranged in a regular, multi-dimensional lattice structure.

Ionic Bond

An ionic bond forms between a metal and a non-metal. Atoms tend to gain or lose electrons to achieve a stable configuration:

• Metals tend to lose electrons to form positive ions (cations).
• Non-metals

Catalyst

A catalyst is a substance present in a chemical reaction that produces a change in its speed without being consumed during its course. It participates in the reaction but is not altered by it. There are positive catalysts that increase the rate of reaction and negative catalysts that reduce the rate of reaction.

Oil

Oil is a mixture of organic substances—liquid, gaseous, or even solid in solution—mainly abundant in hydrocarbons. Simple hydrocarbons, such as methane, exist, as well as more complex ones that can have up to 40 carbon atoms. Organic compounds with oxygen, such as phenols, are also present. Oil is composed mainly of carbon, a lower percentage of hydrogen, and an even smaller percentage of other elements like nitrogen,... Continue reading "Chemical Concepts Explained: Catalysts, Oil, and Molecular Forces" »

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" »