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

Understanding Atomic Structure

Atomic Number

The atomic number (Z) is the number of protons in an atom. In a neutral atom, the number of electrons is equal to the number of protons.

Mass Number

The mass number (A) of an atom is the total number of protons (Z) and neutrons (n) in the nucleus. Therefore, A = Z + n.

Atomic Mass

The atomic mass is the mass of a single atom. Because the masses of atoms are very small, they are typically expressed using atomic mass units (amu) rather than SI units.

Isotopes

Isotopes are atoms of the same element that have the same atomic number but different mass numbers. Isotopes of an element have the same number of protons but different numbers of neutrons.

Atomic Orbitals (Electron Shells)

Atomic orbitals, or electron... Continue reading "Understanding Atomic Structure: Number, Mass, Isotopes, and Ions" »

Cytology Fixatives

Solution: Cytology fixatives, formerly employing ether/alcohol 96 in equal parts, are now rarely used due to the hazardous nature of ether. The 96% alcohol is most often used. The procedure involves immersing the preparation in the fixative bath for a minimum of 10 to 15 minutes. Other alcohols, such as 100% methanol, 80% propanol, and 80% isopropanol, can also be used. Citospray is used in samples obtained by forced exfoliation.

Sample Types in a Cytology Laboratory

Samples that can reach the lab from samples obtained by:

• Forced exfoliation: Rubbing or scraping with various instruments. This is applied to the skin and organs accessible from the outside.
• Spontaneous exfoliation: Samples containing spontaneously exfoliating

Understanding the Atom: Fundamental Building Blocks

The atom is the smallest indivisible particle from which all matter is built. While all atoms are fundamental, they differ according to the specific element they constitute. Despite their small size, atoms contain several internal parts and particles. Historically, various models, such as those proposed by Thomson and Rutherford, attempted to explain atomic structure. We will focus on the most current and widely accepted model, the Bohr model.

The Atomic Nucleus: Protons and Neutrons

The central part of the atom is the nucleus, which contains two primary types of particles:

• Neutrons: Particles with no electric charge (charge = 0).
• Protons: Particles with a positive electric charge (charge = +1)

ZOE Impression Paste

Advantages: Good adhesion, adequate working time, requires no insulation to the plaster model, is fluid allowing copying of fine details, and is economical.

Disadvantages: The Eugenol is acidified, and some patients are allergic to eugenol.

Elastomers

Organic materials formed by weak interaction with polymer molecules, forming a three-dimensional network with elastic properties.

Mercaptan Elastomers

Elastic impression materials with mercaptan groups in the polymer chain, which when hardened, forms a semisolid paste.

Synonyms: Polysulphide rubber, synthetic rubber, tiocoles.

Commercial presentation: Pasta-pasta

Consistencies: Light, regular, heavy.

Chemical Composition:

Paste: Polysulfide polymer (base), titanium dioxide (filler) can... Continue reading "Dental Impression Materials: ZOE Paste & Elastomers" »

Chemical Reaction Rates: Fundamentals and Catalysis

Key Concepts in Chemical Kinetics

• Rate Law

  The speed of a reaction is directly proportional to the concentrations of the reactants raised to some exponent.

• Collision Theory

  This theory states that a greater concentration of reactants leads to more frequent collisions, thereby increasing the reaction rate.

• Reaction Profile

  A diagram that illustrates the progress or development of a chemical reaction.

Factors Influencing Chemical Reaction Rates

The speed of a chemical reaction depends on several critical factors:

• Nature of Reactants: The inherent properties of the reacting substances.
• Concentration: Higher concentrations generally lead to faster reactions.
• Physical State of Reactants: This factor involves

1. 1. Specific Volume and Critical Conditions

   Statement: The specific volume of a gas is the volume that would occupy 1 mole of that gas at its critical temperature and pressure. (False)

   Correction and Explanation:

   This statement is false. The critical volume is the volume occupied by one mole of a substance at its critical point. Specific volume, by definition, is the volume per unit mass of a substance. The original statement incorrectly defines specific volume in terms of molar volume at critical conditions.

2. 2. Adiabatic Processes and Heat Transfer

   Statement: When there is heat loss to the environment, a process cannot be adiabatic. (True)

   Explanation:

   An adiabatic process is fundamentally defined by the absence of heat transfer (Q=0) to or from the

Key Concepts in Metallurgy and Materials Science

• The higher the ideal critical diameter of steel, the lower its hardenability.
• The greater the hardenability of steel, the greater the hardness of martensite that forms upon quenching.
• The lower the specific heat of a bath, the more energetic the cooling it produces during tempering.
• Examples of transformations include diffusion and martensitic transformations.
• Standard heat treatment can result in a coarser grain size in steels compared to those annealed at the same temperature.
• Hadfield steel, with more than 1% carbon and 14% manganese, is an example of martensitic steel.
• Magnesium is the element that causes the graphitization of white cast irons.
• Standard heat treatment produces a coarser grain size

Fundamental Chemical Definitions

Molecule

The union of atoms.

Lattice

A continuous structure of millions of atoms.

Chemical Bond

The attractive force that keeps atoms united in a molecule or a crystal.

Elementary Chemical Substance

Atoms of the same element that unite.

Chemical Compound

Atoms of different elements that unite.

The Octet Rule

Atoms of different chemical elements tend to join with other atoms to have eight electrons in their outermost shell, known as an octet, to achieve greater stability.

Types of Chemical Bonds

Ionic Bond

The transfer of valence electrons. The ionic bond is the union of oppositely charged ions through electrostatic forces of attraction. In this case, the elements bond to achieve a noble gas electron configuration.

Ionic Crystal

A... Continue reading "Chemical Bonding and Material Attributes" »

Substances, Mixtures, and Separation Techniques

1. Pure Substances vs. Mixtures

• Distilled Water: Pure substance/compound
• Tap Water: Mixture/homogeneous
• Diamond: Pure substance/element
• Gasoline: Mixture/homogeneous
• Wine: Mixture/homogeneous
• Air: Mixture/homogeneous

2. Dalton's Theory

• Matter is made up of indivisible and indestructible atoms.
• All atoms of the same element are equal in mass and properties.
• Compounds are formed by the combination of different elements.

3. Separation Techniques

• Screening: Separates solid particles of different sizes. Instrument: sieve.
• Filtration: Separates solids from liquids. Instrument: filter.
• Evaporation: Separates solids from liquids when the liquid is not needed. Works best with homogeneous mixtures. The process is faster

Aluminum

Aluminum is used in telescopes. Tempered powder paint is used in metal protection and the preparation of alloys. Aluminum forms alloys with other metals. Duralumin, an aluminum alloy, is used in aeronautics because it is very lightweight and has great resistance.

Aluminothermy

Aluminothermy is a metal extraction procedure that reduces metal oxides using aluminum powder. Metals such as chromium, manganese, and molybdenum are obtained using this method.

Salts of Aluminum

Important industrial salts are called alum (double salts).

Natural Aluminum

Aluminum is not found free in the Earth's crust. It is named after these characteristics:

1. Alumina
2. Hydroxide
3. Silicates

Obtaining Aluminum

Aluminum is extracted using the electrolytic method. Bauxite and cryolite... Continue reading "Aluminum, Copper, Polymers, and Ceramics: Properties and Uses" »