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

Bohr's Atomic Model

Rutherford's atomic model was incomplete and unstable. The Danish physicist Bohr proposed a new atomic model based on four postulates, among which was the continuity of orbits:

1. The atom consists of a nucleus with a positive charge and contains most of the mass of the atom, and a cortex in which the electrons are moving.
2. Electrons move in circular orbits around the nucleus.
3. Only orbits in which the electron's angular momentum is a multiple of Planck's constant are possible. In these orbits, the electron does not emit or absorb energy.
4. The step from one orbit to another involves the absorption or emission of radiation. The atom will absorb or emit only the radiation just enough to move from one orbit to another.

The Bohr model can... Continue reading "Bohr and Rutherford Atomic Models: Key Differences" »

Metals, Metalloids, and Non-metals

• Metals: Good conductors of electricity.
• Metalloids: Intermediate between metals and non-metals.
• Non-metals: Poor conductors of electricity.

Atomic Orbitals

The last significant electron shell fills with gas.

Examples of Orbitals

• S orbital
• P orbital
• D orbital
• F orbital

Orbital Shapes

• Orbital S: Spherically symmetric around the atomic nucleus.
• Orbital P: Two flattened areas at the point of contact, oriented according to the coordinate axes.
• Orbital D: Four lobes of alternating signs, with the last being a double lobe surrounded by a ring.
• Orbital F: More complex shapes.

Quantum Principles

1. Pauli Exclusion Principle: No two electrons can have the same quantum numbers.
2. Aufbau Principle: Electrons fill the lowest energy levels first.

Periodic Table Structure

What is the name and number of the columns in the periodic system of elements? They are called families or groups. There are 18 columns.

What is similar about elements in the same column? They have a similar electronic structure in their outermost shell.

What is the name and number of the horizontal rows in the periodic system of elements? They are called periods. There are 7 periods.

Explain what is similar about elements in the same row. They have the same number of electron shells.

Properties of Chemical Compounds

Characteristics of Ionic Compounds

• Very stable, requiring a lot of energy for the dissolution of their crystalline structure.
• Solid at room temperature.
• Do not conduct electricity in the solid state.
• Have high melting

Porcelain: Aesthetic Refractory Ceramic Material

Porcelain is an aesthetic refractory ceramic material constituted by a combination of a crystalline mineral phase and a glass phase.

Chemical Composition

It features a cored structure comprising a crystalline mineral phase and a glass (vitreous) phase.

Crystalline Mineral Phase Components:

• Feldspar (80%): Provides the glassy phase, crystalline phase matrix, and contributes to a low fusion temperature.
• Quartz Silica (15%): Enhances resistance and refractory properties.
• Alumina (1%): Further contributes to resistance and refractory characteristics.
• Kaolin Clay (3%): Adds strength, color, and acts as a linking agent.
• Metallic Pigment (1%): Used for color.

Glassy Phase Components:

• Silica (65%): Provides strength

Introduction to Chemical Bonding

Chemical bonding is the force that binds atoms, ions, or molecules together to form various substances. When two molecules are linked by intermolecular forces, these are also considered types of attractive forces.

The coordination number refers to the number of ions surrounding a central ion in a crystal lattice.

Types of Chemical Bonds

Ionic Bonds

Ionic bonds result from the electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions). Each positive ion is typically surrounded by the largest possible number of negative ions, and vice versa, forming a crystal lattice.

Lattice Energy

Lattice energy (E_lattice) is the energy released when one mole of a solid ionic compound is... Continue reading "Chemical Bonding Fundamentals and Material Characteristics" »

1. Does the Cathode Ray Tube (CRT) Use an Electron Gun?

Yes, the picture tube television (CRT) relies on an electron gun to generate the image.

2. Types of Cathode Ray Tubes (CRTs)

The main types of CRTs encountered are:

• Delta Tube
• In-line Tube
• Trinitron Tube
• Precision In-Line (PIL) Tube

3. LCD vs. TFT: Passive and Active Matrix Differences

How is an LCD screen different from a TFT screen?

Traditional LCD screens often utilize a passive matrix structure, whereas TFT (Thin-Film Transistor) screens employ an active matrix structure, which allows for faster response times and better image quality.

4. CRT Degaussing: Purpose and Process

Reasons for Degaussing

The movement of electron beams within the CRT is based on magnetic fields generated by deflection coils.... Continue reading "Display Technology Fundamentals: CRT, Plasma, and Matrix Screens" »

Defining Raya

Raya refers to the color of a mineral when it is pulverized into a fine powder.

Defining Brightness and Its Significance

Brightness

Brightness describes the general appearance of a mineral's cool surface when observed under reflected light. It is influenced by factors such as the refractive index, degree of transparency, and surface polish.

Types of Brightness

Metallic

Minerals with a metallic brightness exhibit a glow similar to polished metals and have a high refractive index.

Non-Metallic

Non-metallic minerals are typically light in color and have a low refractive index. They can be further classified as:

• Silky (resembling silk)
• Pearly (exhibiting a peel-like appearance)
• Earthy (scattering light completely)
• Greasy (having an oily appearance)

Ferrous Metals: Production, Treatments, and Properties

Mechanical Treatments for Metals

Mechanical treatments improve the characteristics of metals through controlled mechanical deformation.

Types of Mechanical Treatments:

• Hot Mechanical Treatment: Involves heating the metal followed by stretching or deformation.
• Cold Mechanical Treatments: Deformation performed at room temperature.

Related Surface Treatments:

Examples include metallization and chrome plating.

Ferrous Metals: Definition and Classification

Ferrous metals are those containing technically pure Iron (Fe) as their basis. Fe is a magnetic, blue-white metal material, known for being ductile and malleable. Its melting point is 1535 °C.

Classification of Ferrous Metals by Carbon Content

• Industrial

Pure Substances and Mixtures

Substances are formed by the same particles (either atoms or molecules). They cannot be decomposed into other substances by simple procedures. These include elements and compounds.

Mixtures are formed by two or more substances. Mixtures, whether homogeneous or heterogeneous, can always be separated by physical means such as filtration, decantation, distillation, or chromatography.

Separation Methods

Separation methods are generally categorized based on the type of mixture:

• Mechanical Methods: Most useful for heterogeneous mixtures.
• Thermal Methods: Appropriate for homogeneous mixtures.

Mechanical Separation Methods

Sedimentation

Widely used in mining to separate ore from gangue by gravity.

Settling (Decantation)

Used when

Biophysics II

Colloids

Colloids are suspensions of very small particles (micelles), even much larger than the dispersed molecules within a liquid. They are also called pseudo-solutions or colloidal solutions.

State of Sol and Gel

Protoplasmic colloids undergo sol-gel processing, also called reversal or phase change. Colloids present an intermediate state between solid, liquid, and gas. States in the protoplasm of sol and gel usually alternate due to changes in concentration. The most important sols in biology are protein dispersions in water.

Types of Colloids According to the Physical State of the Phases

The dispersant phase can be a solid, liquid, or gas, just as the dispersed phase may be liquid, solid, or gaseous. The passage from a sol to a... Continue reading "Biophysics II: Colloids, Properties, and States" »