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

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.

Metallic Materials

Metallic materials are inorganic substances containing one or more elements. They may contain metals and also some non-metallic elements. The metallic elements include iron, copper, aluminum, nickel, magnesium, and titanium. Non-metallic elements include carbon, nitrogen, and oxygen.

Characteristics of Metal Components

• Have a crystalline structure
• Are good thermal and electrical conductors
• Many have mechanical resistance and are ductile at room temperature
• Can also exhibit high strength at elevated temperatures

A metal alloy is a combination of two or more metals. They are normally divided into two classes:

• Ferrous metals and alloys that contain a high percentage of iron
• Nonferrous metals and alloys containing no iron or relatively

Why Life Is Based on Carbon and Not on Silicon

Although silicon (Si) also has four electrons in its valence shell and is much more abundant in the Earth's crust than carbon (C), life is based on C and not on Si. This is because C-C, C=O, and C-N bonds are weak enough to form stable chains and rings, while also being able to break to make way for other molecules. This allows living organisms to obtain the energy contained in these bonds. In contrast, Si-Si and Si-O-Si-O chains are so stable that they are unalterable.

Descriptive Biology

Descriptive biology is based on the simple observation of the structure and functioning of living things, to make descriptions of what is observed. Until the 17th century, it was based solely on simple observation... Continue reading "Carbon-Based Life and the Scientific Method" »

Types of Materials

Materials are substances whose properties make them useful for the fabrication of structures, machinery, and other products.

Material Classification Groups

Materials are typically classified into groups:

• Metals and Alloys (e.g., iron, steel, aluminum)
• Polymers (e.g., nylon, polyurethane)
• Ceramics and Glass (e.g., alumina, magnesia)
• Composite Materials (e.g., wood, cermets)

Material Properties

Key material properties include:

• Chemical Properties
• Physical Properties
• Mechanical Properties
• Aesthetic and Economic Properties
• Fabrication Properties

Chemical Properties

Chemical properties include behavior related to oxidation and corrosion.

Oxidation

Oxidation occurs when a material combines with oxygen, forming oxides.

Corrosion

Corrosion is a form... Continue reading "Understanding Material Properties and Classes" »

Understanding Chemical Oxides

Binary combinations between oxygen and all other chemical elements except the noble gases and fluorine.

Formulating Oxides

Oxides have the following general formula: X₂O_n, where:

• X is the symbol of the other element.
• 2 corresponds to the valence of oxygen.
• O is the symbol for oxygen.
• n is the valence of the other element (metal or nonmetal).

Naming Oxides: Three Classifications

Oxides are named using three classifications: Traditional, Systematic, and Stock.

Traditional Nomenclature for Oxides

Basic Oxides: These result from the combination of oxygen and a metal.

• If the metal has a single valence, the oxide is named "Oxide" followed by the name of the metal.

Examples:

• CaO: Calcium Oxide
• Na₂O: Sodium Oxide

• If the metal has two

Laws of Melting

When a pure substance melts, it exhibits specific behaviors:

1. It melts at a specific temperature, called the melting point.
2. While melting, the temperature remains constant, even with the coexistence of solid and liquid phases.
3. All pure liquids, when sufficiently cooled, solidify at the same temperature at which they melt.
4. During solidification, the temperature remains constant.

Melting Point and Solidification

The melting and solidification points of a pure substance are characteristic properties that can be used to identify it.

A substance whose temperature varies during a state change cannot be considered a pure substance.

Vaporization

Vaporization is the change of state from liquid to vapor (or gas). It can occur in two ways: boiling... Continue reading "Understanding Changes of State: Melting, Boiling, and Sublimation" »

Properties of Matter

Characteristic and General Properties

There are some characteristic properties which allow us to identify substances (e.g., density, conductivity, color) and some general properties common to all types of matter (e.g., mass, volume, temperature).

Pure Substances

Types of Pure Substances

A pure substance is a form of matter with a constant composition that does not change regardless of physical conditions. Pure substances are categorized into two main types:

Compounds

Compounds are pure substances that can be chemically decomposed into simpler substances.

Elements

Elements are pure substances that cannot be decomposed into simpler substances by any chemical or physical procedure.

Examples of Pure Substances

• Compounds: Distilled water,

Since antiquity, attempts were made to understand matter by dividing it into its tiny parts. The Greeks called these tiny, allegedly invisible parts of matter 'atoms'.

Dalton's Atomic Theory

In 1808, John Dalton took the ideas of the Greeks and further developed them into a comprehensive theory. Key definitions and postulates from his theory include:

• Matter consists of indivisible particles called atoms.
• An element is a substance composed of identical atoms.
• A compound is a substance formed by atoms of two or more different elements combined in fixed ratios.

It is important to note that Dalton believed atoms were indivisible, a concept later disproven by the discovery of subatomic particles.

The Electrical Nature of Matter

Experiments can easily demonstrate... Continue reading "Unraveling the Atom: From Ancient Ideas to Modern Structure" »