Unidad 1: La materia se organiza

Fundamental Definitions of Matter: Mass, Weight, and Volume

The universe is composed entirely of matter, which encompasses everything from living beings and computers to water, food, clothing, and even the air. Matter is formally defined as anything that possesses mass, weight, and volume. Because it occupies a specific place in space, matter is both observable and measurable. Within this study of matter, a "body" is defined as a specific portion of matter that has well-defined limits. While some bodies are easy to distinguish, such as a pencil or a tree, others are more complex to define, such as the specific boundaries of a body of water in a lagoon.

Mass is defined as the total quantity of matter contained within a body. When comparing two bodies made of the same material but of different sizes, the larger body will consistently have a greater mass than the smaller one. Mass is measured using a balance and is typically expressed in units of kilograms ($kg$) or grams ($gr$).

Weight is the force of attraction, specifically gravity, exerted by the planet Earth on all bodies. Unlike mass, weight depends on two distinct factors: the mass of the body and the gravity of the planet. Weight is measured using an instrument called a dynamometer and is expressed in Newtons ($N$).

Volume represents the space occupied by a body. The methods for measuring volume vary depending on the body's physical shape and its state of matter. Common units for expressing volume include cubic meters ($m^3$), cubic centimeters ($cm^3$), liters ($l$), or milliliters ($ml$). An example of an extreme material regarding these properties is Aerogel, which is an ultra-lightweight solid material with an enormous capacity for thermal insulation.

Classification of Materials and Their Properties

Materials are defined as the various classes of matter that constitute bodies. Common examples include plastic, paper, steel, meat, sugar, and glass. In the field of Natural Sciences, the properties of materials are categorized into two types: extensive and intensive properties.

Extensive Properties are those that depend directly on the quantity of matter or mass being analyzed. These include mass, weight, volume, and general dimensions such as length, width, and diameter. For instance, requiring a bar of 25 Newtons ($25\,N$) or purchasing 500 grams ($500\,gr$) of sugar refers to extensive properties.

Intensive Properties are independent of the quantity of matter or mass analyzed. Examples include color, smell, taste, texture, and temperature. These properties are essential for selecting materials for specific uses. For example, sulfur is yellow, alcohol boils at $78^\circ C$, and water freezes at $0^\circ C$. These are inherent characteristics of the substance regardless of how much of it is present.

Specific Intensive Properties of Materials

Materials possess various intensive properties that determine their suitability for infrastructure, manufacturing, or consumer goods. These are categorized into several functional groups.

Mechanical properties describe how materials behave when subjected to external forces. Hardness is the resistance a material offers against being scratched by another; the diamond is the hardest known material, while glass is harder than wood. Plasticity is the ability to deform permanently without breaking, seen in chewing gum or plasticine. Ductility allows materials to be deformed into wires or cables, as seen in copper and steel. Malleability is the property of deforming into thin sheets, common in aluminum, copper, gold, and silver. Elasticity is the ability to return to an original state after a force is removed, such as a rubber band. Tenacity is the resistance to breaking when hit, exemplified by steel, while Fragility is the tendency to break easily upon impact.

Electrical properties determine the behavior of a material when electricity passes through it. Electrical Conductors, like copper, allow current to pass easily. Electrical Insulators, such as rubber, wood, plastic, or porcelain, prevent the flow of current. Semiconductors, such as Silicon, Germanium, and Selenium, allow current to pass only under specific conditions like certain temperatures.

Thermal properties involve the transmission of heat. Thermal Conductors, including copper, gold, silver, steel, aluminum, and iron, transmit heat efficiently. Thermal Insulators, such as wood, plastic, glass, cork, rubber, and polystyrene (telgopor), block or isolate the passage of heat.

Optical properties are defined by how light interacts with the material. Opaque materials, like wood, stone, and metals, do not let light pass through. Transparent materials, like glass or clean water, allow light to pass through clearly. Translucent materials, such as frosted glass or turbid water, allow only part of the light to pass through.

Acoustic properties involve sound transmission. Acoustic Transmitters include wood, metals, and water. Acoustic Insulators, such as cork, are used to block sound. Finally, Magnetic properties refer to the capacity to attract metallic materials such as iron, nickel, and cobalt.

Origins and Environmental Effects of Materials

Materials can be classified according to their origin into two main groups: Natural and Artificial. Natural materials are found in nature and can be of Animal origin (leather, wool, silk), Vegetal origin (cotton, wood), or Mineral origin (aluminum, silver, salt, coal, petroleum). Artificial materials are manufactured by humans using natural materials as precursors. For example, paper is made from wood, glass is made from minerals, plastics are synthesized from petroleum, and cardboard is produced from wood.

Materials are also classified by their environmental impact. Recyclable materials, such as glass, cardboard, paper, and plastic, undergo processes to be converted back into raw materials or new products to reduce waste. Toxic materials are harmful to the environment and living beings; these include pesticides in food, heavy metals like lead or arsenic in water, and chemical wastes in streams. Biodegradable materials are those that decompose through the action of bacteria, fungi, and other living organisms. While most materials are technically biodegradable, many require extremely long periods to destroy themselves completely.

Physical States of Matter and the Kinetic-Molecular Model

Matter exists in three primary physical states or states of aggregation: solid, liquid, and gaseous. Water is a unique example that can exist in all three states simultaneously (as seen in the water cycle).

Solid matter has its own defined shape and volume and is incompressible. Examples include gold, wood, and iron. Liquid matter has a defined volume but adopts the shape of its container and is very difficult to compress. Examples include alcohol, vinegar, and water. Gaseous matter has neither a defined shape nor volume, occupying the entire space of its container, and is highly compressible. Examples include carbon dioxide, oxygen, and water vapor.

To explain these behaviors, scientists use the Kinetic-Molecular Model. This model posits that matter is formed by infinitely small particles that are invisible to the naked eye. Between these particles exist forces of attraction (drawing them together) and repulsion (pushing them apart). These particles possess kinetic energy, which is the energy of motion. Kinetic energy increases as temperature increases and decreases as temperature decreases.

In the solid state, particles are very close together with restricted movement; attraction forces predominate, and kinetic energy is at its minimum. In the liquid state, particles have greater movement and are more spaced out; attraction and repulsion forces are in equilibrium, and kinetic energy is at an intermediate level. In the gaseous state, particles are very separated with chaotic movement; repulsion forces predominate, and kinetic energy is at its maximum.

Practical Applications and Workshop Procedures

A notable practical application of the concepts of biodegradable materials is the creation of biodegradable planters using yerba mate. This process involves collecting used yerba mate, drying one portion in the sun while keeping another damp. A thick paste (engrudo) is made by mixing flour and water over low heat, with vinegar added to prevent mold. The yerba is mixed into this paste to form a moldable mass. This mass is pressed into a mold lined with plastic wrap and dried in the sun for at least a day until it becomes firm and lighter in color. Finally, a drainage hole is drilled to protect plant roots.

Another application is found in the workshop "Símbolos patrios reciclados," where students create patriotic cockades (escarapelas) using recyclable materials to distribute throughout the school, demonstrating the utility of recycling in community settings.

Questions & Discussion

The Mass vs. Weight Debate: Juan and María discussed whether a kilogram ($1\,kg$) of cotton weighs the same as a kilogram ($1\,kg$) of lead. Juan argued the lead weighs more, but María is correct; since both have a mass of one kilogram, the gravitational force (weight) acting on them is identical, although their volumes differ significantly.

Galileo's Vacuum Experiment: A common physics demonstration involves dropping a bowling ball and feathers. In a normal environment, the bowling ball falls faster because of air resistance. However, within a vacuum chamber where air is removed, both fall at the exact same rate. This confirms Galileo Galilei's discovery (around the late 16th/early 17th century) that gravity acts equally on all masses in the absence of air resistance.

Identifying Matter and Properties: Classifying various items into categories is common in physical chemistry. For example, a liter of water refers to volume, while a 784 Newton value ($784\,N$) refers to weight. Light traveling in a vacuum at $299,792,458\,m/s$ is classified as "non-matter," as is the feeling of fear or the sunlight mentioned in narrative texts, because they lack mass and do not occupy space. Conversely, a syringe made of plastic or a needle made of stainless steel are bodies composed of specific materials (plastic and steel).", "title": "Study Guide for Physical Chemistry Unit 1: The Organization of Matter"}