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

Ionic Versus Covalent Chemical Bonds

Ionic Bonds

The ionic bond forms between elements with very different electronegativities. This involves the transfer of electrons from the less electronegative element to the most electronegative one. This process forms respective positive ions (cations, which lose electrons) and negative ions (anions, which gain electrons).

This type of bond typically occurs between elements at opposite ends of the periodic table: specifically, between highly electronegative elements (nonmetals) and less electronegative elements (metals).

Properties of Ionic Compounds

1. High melting and boiling temperatures.
2. Solid at room temperature.
3. The crystal lattice is very stable, making it very difficult to break.
4. They are hard (scratch resistant)

Mendeleev's Criteria for Sorting Elements

Mendeleev sought a system linking elements based on the properties of their simple substances. He ranked them in increasing order of their atomic weights, from hydrogen to uranium. The arrangement ensured that elements with similar properties remained in the same column.

Mendeleev's Prediction and Gaps

Mendeleev noted that some known elements did not fit his structure, so he left empty spaces ('holes') to maintain correct positioning based on properties. Convinced his system was correct, he assumed these gaps would be filled by undiscovered elements.

Acceptance of Mendeleev's Solution

In 1869, the scientific world was skeptical of his predictions, but Mendeleev did not wait long for his work to be recognized.... Continue reading "Mendeleev's Periodic Table: Structure and Element Properties" »

Dalton's Atomic Theory and Postulates

In 1808, the English scientist John Dalton (1766-1844) published his ideas about the constitution of matter. These postulates can be summarized using modern language:

• Matter is comprised of extremely small particles called atoms, which are indivisible and indestructible.
• Each chemical element has atoms that are all identical, but different from those of other chemical elements.
• According to Dalton, a chemical compound is formed by the union of atoms of different elements of the same type and always in the same proportion.

Chemical Elements, Compounds, and Electrolysis

• Chemical element: A substance that cannot be decomposed into other simpler substances because it consists of a single type of atom.
• Composite (Compound)

Materia: Pure substances: substances that is form by the same kind of particles (molecules, atoms…).  Elements: form by the same kind of atom. We can’t divide them. Ej. P, O, C… Compounds: form by the same kind of molecules. We can divide them. Ej. H₂O, CO₂. Mixtures: substances that is form by different kinds of particles.  Homogeneas: you can’t see the different components. Ej. Seawater. Heterogeneas: you can see the different components. Ej. Granite.
1. The atom: is the smallest unit of a chemical element that retains its identity and properties that can not be divided by chemical processes.Types: Proton: have a positive charge. Neutron: don’t have charge. Electron: have negative charge.
4. Rutherford’s atomic model:
Rutherford... Continue reading "Coh3 chemical name" »

The Pluralistic School

Speculation about the physical world, initiated by the Ionians, was continued in the 5th century BC by Empedocles and Anaxagoras. They developed philosophies which replaced the description of a first Ionian substance only by the assumption of a plurality of substances. Empedocles maintained that all things are composed of four irreducible elements: air, water, earth, and fire, combined or separated by two opposing forces as a process of alternation: love and hate. Through this process, the world evolves from chaos to form and back into chaos again, in a repeated cycle. Empedocles considered the eternal cycle as the true object of religious worship and criticized the popular belief in personal gods, but failed to explain... Continue reading "Pluralism and Atomism in Ancient Greek Philosophy" »

Understanding Chemical Solutions

A solution is an optically homogeneous, single-phase system. It is composed of two main components: the solute and the solvent.

Types of Chemical Solutions

• Unsaturated: These are solutions containing less solute than what is required to reach saturation.
• Saturated: These contain the maximum amount of solute that can be dissolved under specific conditions of pressure and temperature.
• Supersaturated: These contain more solute than can be maintained in stable equilibrium under given conditions of pressure and temperature.

Solubility and Its Coefficients

Solubility is a measure of the ability of a particular substance to dissolve in another. The solubility coefficient is a value associated with each element or compound... Continue reading "Fundamental Principles of Chemical Solutions and Phases" »

Key Properties of Chemical Substances

Ionic Compounds

• Solid at room temperature
• Form crystal lattices, not individual molecules
• Soluble in water
• Conduct electricity when molten or dissolved
• High hardness and brittle
• High melting and boiling temperatures

Molecular Substances

• Composed of molecules
• Weak intermolecular forces
• Often gaseous (e.g., O₂, N₂, NH₃) or liquid (e.g., H₂O)
• Soft solids
• Low melting and boiling temperatures
• Poor electrical conductors
• Not very soluble in water

Covalent Crystals

• Solid
• Form crystals with atoms joined by covalent bonds in three dimensions
• Insoluble in all solvents
• Generally do not conduct electricity (except graphite)
• Very hard and brittle
• High melting and boiling temperatures (1200 to 3600 °C)

Metals

• Solid at room temperature (except

Understanding Uranium and Nuclear Fuel

Natural uranium is composed of three isotopes: Uranium-238 (U-238), Uranium-235 (U-235), and Uranium-234 (U-234). While U-238 is fertile and can be converted to fissile material, U-235 is the primary fissionable isotope used for power generation. Natural uranium ore cannot be used directly as nuclear fuel because the concentration of U-235 is too low. Therefore, uranium needs to be enriched to achieve a U-235 concentration of more than 3%. To produce one kilogram of enriched uranium, approximately eight kilograms of natural uranium must be purified and refined.

How Nuclear Power Plants Operate

Nuclear power plants utilize uranium as their primary energy source, harnessing nuclear fission to generate electricity.... Continue reading "Nuclear Energy Fundamentals: Fuel Cycle, Power, and Waste" »

Understanding Vaporization and Boiling

The transition from liquid to vapor, known as vaporization, can occur in two primary ways: either only on the surface of the liquid (evaporation) or throughout its entire volume (boiling).

When a liquid in a container is heated, its vapor pressure increases until it equals the atmospheric pressure. At this point, vapor forms throughout the entire mass of the liquid and escapes. Boiling is a specific form of vaporization.

The boiling temperature is a characteristic property of each substance, but it varies with pressure. Vapor pressure itself depends on temperature and increases as temperature rises.

Intermolecular Forces and Boiling Point

The constitution of a liquid significantly influences its boiling behavior.... Continue reading "Fundamentals of Vaporization, Distillation, and Adsorption" »

Properties and Behavior of Liquids

Fluidity is a property of liquids and gases that gives them the ability to pass through openings smaller than themselves, provided the opening is at the same level or lower than the container in which the fluid resides. This behavior distinguishes fluids from the solid state of matter.

Liquid State and Shape

Liquid is one of the four states of matter. A liquid is a fluid whose volume remains essentially constant under given temperature and pressure conditions, and its shape conforms to the container that holds it. A free droplet, when not acted on by external forces, tends toward a spherical shape due to surface tension. ^[1] In a gravitational field, a liquid instead conforms to the shape of its container.

Pressure