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

Water: The Foundation of Life

Life on Earth began in water, evolving over 3 billion years before conquering land. Water continues to be essential for all living beings.

Water's Essential Role in Biological Systems

The unique properties of cell membranes are due to their particular structure, which in turn is due to the tendency of the phospholipids that compose them to form bilayers in aqueous media.

• Water is Essential for Life: It is a constituent of cells (its percentage depends on cell type and physiological state), provides a means of transport for solutes over short and long distances, and is involved in cell metabolism as a substrate, product, or reagent.
• Turgor: A feature of plant cells where water exerts pressure on the cell wall. It is

Chemical Bonds and Substance Types

The enormous variety of substances is possible thanks to the fact that the atoms of most elements have a great ability to join other atoms, either among different elements or atoms of the same element. These forces are known as chemical bonds. The result of chemical bonding ranges from a discrete group of atoms, called a molecule, to a structure of millions of atoms ordered regularly in space, forming a lattice or crystal.

Classifying Chemical Substances

Elements and Compounds

If atoms of the same element join, they form an elemental substance, whereas if they are different elements, they form a chemical compound.

Molecular Substances

Substances which are formed by molecules are called molecular substances. The... Continue reading "Chemical Bonds and Substance Classification" »

Electron Spin and Orbitals

Spin refers to the movement of an electron around the nucleus and on its own axis. There are two possible spin directions: +1/2 and -1/2. When two electrons have opposite directions of rotation, they are represented with small arrows, one pointing up and the other down.

An orbital is occupied when it contains two electrons. An orbital with a single unpaired electron is represented by a single arrow. Orbitals are represented as rectangles called quantum boxes, within which the electrons are indicated.

The electronic configuration of an atom describes how the electrons are arranged within the atom.

Hund's Rule

Hund's rule states that an electron cannot completely fill an orbital until all orbitals within that sublevel contain... Continue reading "Electron Configuration and Chemical Bonding Basics" »

Intermolecular forces (IMFs) are attractive forces that exist between molecules. They are responsible for holding molecules together in condensed phases (liquids and solids) and influence various physical properties such as melting points, boiling points, and solubility.

Dipole-Dipole Interactions

These forces occur between molecules that possess a permanent nonzero dipole moment. In such molecules, electrons accumulate in one part (creating a negative pole), while another part becomes electron-deficient (forming a positive pole). If the dipole is sufficiently large, the electrostatic forces between these dipoles can significantly influence the substance's properties. For instance, substances with strong dipole-dipole interactions often have... Continue reading "Intermolecular Forces: Molecular Interactions and Properties" »

Mol

The unit of amount of substance in the SI. It is the amount of substance that contains as many basic entities as there are atoms in 12 g of the isotope carbon-12.

Avogadro's Number (NA)

One mole contains Avogadro's number of particles: NA = 6.022045 × 10²³.

Molar Mass (M)

Mass of one mole of atoms or molecules. The numerical value of molar mass in grams matches the value of the mass in amu of its formula.

Molar Volume

Volume of 1 mole of a substance at a certain temperature (the temperature must be stated), whether solid, liquid, or gas.

Following Avogadro's principle, 1 mole of gas occupies the same volume when measured under the same conditions of pressure (p) and temperature (T), irrespective of the gas. Under standard conditions (0 °C and... Continue reading "Fundamental Chemistry Concepts & Laws" »

Chemical Reactions

A chemical reaction is a process in which one or more substances react to form other substances with different properties.

Chemical Reactions and Chemical Equations

The chemical equation is the symbolic representation of a chemical reaction.

Activation Energy

For a chemical reaction to be possible, particles must collide with a minimum energy.

Reaction Energy

The energy exchange that occurs in the course of a chemical reaction is called the energy of reaction.

Speed of Reaction

The speed at which a chemical reaction takes place.

Factors Influencing the Reaction Rate

• Nature of Reagents: Generally, covalent substances lead to slow reactions at room temperature, while ionic substances react quickly when dissolved.
• Temperature: The reaction

Fundamental Chemical Substances: Elements and Compounds

Defining Simple Substances: Elements

Simple substances, or elements, are the basic building blocks of matter. They combine in fixed proportions by mass to form compounds.

Classification of Elements

• Metallic Elements

  Located on the left side of the periodic table. All are solids at room temperature, except mercury (Hg), which is a liquid with a melting point of -39 °C.

• Nonmetals

  Found on the right side of the periodic table. Examples include carbon (C), nitrogen (N), phosphorus (P), oxygen (O), sulfur (S), selenium (Se), and the halogens: fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). They exist in various physical states; for instance, sulfur is solid, chlorine is gaseous, and bromine

Bioelements: Chemical Basis of Life

Bioelements are the chemical elements that constitute living matter. They are classified based on their abundance:

Classification of Bioelements

• Primary Bioelements

  These make up the vast majority of living matter. They include Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), and Sulfur (S) – often abbreviated as CHONPS.

• Secondary Bioelements

  These include Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+), and Chlorine (Cl-). Although present in smaller proportions than primary bioelements, they are essential for life. In aqueous environments within living organisms, they are always found in their ionized forms.

• Trace Elements (Oligoelements)

  These are required in very small amounts.

Understanding Chemical Bonding Principles

Chemical bonding is the union between atoms, molecules, or ions to form larger structures. Molecules, in turn, can be joined by intermolecular forces to form multimolecular structures.

The Octet Rule

To form a stable molecule or structure, atoms that bond tend to gain, lose, or share electrons to complete their valence shell with eight electrons.

Types of Chemical Bonds

Ionic Bond

The ionic bond originates as a result of electrostatic forces exerted between oppositely charged ions, thus forming an ionic crystal. This typically occurs between elements with very different electronegativities.

Covalent Bond

The covalent bond between two atoms occurs when these atoms share electrons so that they complete their... Continue reading "Fundamentals of Chemical Bonding and Material Properties" »

Metal Classification by Density

Non-ferrous metals are primarily classified based on their most important property: density.

• Light Metals: Have a density between 2 and 5 Kg/dm³.
• Ultralight Metals: Their density is less than 2 Kg/dm³.
• Heavy Metals: Possess a density greater than 5 Kg/dm³.

Aluminum's Natural Source and Abundance

From Which Mineral is Aluminum Obtained?

Aluminum is obtained in nature primarily in the form of bauxite. This mineral is composed of aluminum oxide, iron oxide, silicon oxide, and water.

Regions of Bauxite Abundance

This mineral exists predominantly in tropical regions of the planet, for example, Northern Brazil.

Aluminum Production Process

Stages of Aluminum Production

The metallurgical production of aluminum occurs in two main... Continue reading "Aluminum: Properties, Production, and Industrial Applications" »