Evolution of Chemistry and Measurement Concepts
Chemistry Through History
Chemistry has been used since ancient civilizations in activities like cooking and metallurgy. Egyptians and Babylonians achieved great perfection in applying techniques, being masters in handling metals, glass, gold, silver, and clay. However, these peoples gave little importance to the theoretical basis of the processes they carried out daily.
In the 6th century BC, thanks to the emergence of theories about matter through philosophers like Thales of Miletus (625-545 BC) and Anaximander (611-547 BC), the theory of the 4 elements was developed by Aristotle (383-322 BC). These elements were water, air, earth, and fire, which formed matter and defined the fundamental qualities of bodies. Later, in the 5th century BC, Leucippus and Democritus proposed that matter was composed of tiny, indivisible particles they called atoms.
Alchemy (500-1600 AD)
Alchemy was the result of the technical domain and elaboration of Egyptians and Greeks. Alchemists, unlike their predecessors, not only sought to understand the natural world but also desired perfection in themselves. This ideal was materialized in gold. Thus, a large part of alchemy focused its efforts on the manipulation of metals and the search for the philosopher’s stone, a magical substance capable of transforming metals into gold and providing eternal youth. For this purpose, they developed and perfected various instruments and methods, such as alcohol, water bath, alembic, distillation, and sublimation.
Emergence of Modern Chemistry
In the 18th century, the theory of the 4 elements was no longer sufficient to explain the composition of matter. For example, the advancement of knowledge about gases questioned air as a single element, instead of a set of different substances. It was the first time when everything had to be measured, weighed, and verified. The most prominent representative of this trend was Antoine Lavoisier (1743-1794), a French chemist considered the father of modern chemistry, who established that matter is not destroyed but transformed, and demonstrated that air, water, and fire were not elements.
19th and 20th Centuries
During the 19th century, chemistry focused on investigating the nature of matter. John Dalton (1766-1844) presented a consistent proposal on atomic structure, which was complemented by Ernest Rutherford (1871-1937), thus beginning to understand that the atom is composed of smaller particles, not indivisible as its name indicates. The 20th century brought significant changes. In 1905, Albert Einstein presented the theory of relativity, shaking the historical basis of physics and chemistry. In the early 20th century, Marie and Pierre Curie studied radioactivity and discovered two new elements: radium and polonium.
Measurement
Measurement is a physical magnitude that quantifies a pattern called a unit. The result of a measurement is the number of times the unit is contained in the measured quantity.
Physical Magnitudes
Physical magnitudes are those features that can be measured by experts or anyone using a measurement instrument. There are two types of physical magnitudes: fundamental, which do not depend on any other measurement, like time or temperature, and derived, which are expressed as a relation between two or more fundamental magnitudes, like density.
Temperature and Heat
To express the energy of a body, we use a value corresponding to the average energy of molecules. Temperature measures the average energy of the molecules. It is independent of mass, depending only on the speed and mass of each molecule. Heat measures the energy transferred between bodies due to temperature differences.
Heat Units
Heat, as energy transferred due to temperature difference, is measured by the temperature change of a known mass absorbing heat. While joules are a unit of energy, calories are commonly used. A calorie is the heat needed to raise one gram of water’s temperature by one degree Celsius.
Measuring Temperature
Temperature is measured using:
1. Thermometer: A bulb containing a liquid that expands, covered by a tube with a numerical scale. Most materials expand with increased temperature and contract with decreased temperature.
2. Temperature Scales: Defined by two reference points. Common scales include:
- Celsius: Uses water’s freezing (0°C) and boiling (100°C) points.
- Kelvin: Starts at absolute zero (-273°C), where molecular motion ceases.
- Fahrenheit: Used in the U.S., with 180 degrees between water’s freezing and boiling points.
- Rankine: Freezing point is 492°R, boiling point is 672°R, with absolute zero matching Kelvin.
The Scientific Method
Every field of knowledge has its methods, but all follow common principles. Experimental sciences use a method with these stages:
- Observation of Phenomena: Observing phenomena using senses and instruments, then asking questions.
- Formulation of Questions: Asking about the phenomenon’s appearance, circumstances, and characteristics.
- Revision of Previous Work: Consulting sources to learn about existing knowledge.
- Formulation of Hypotheses: Answering the posed questions.
- Experimental Verification: Testing the hypotheses.
- Control Variables: Defining changes that could affect the phenomenon.
- Approach and Dissemination: Publishing or presenting the conclusions.
- Development of Legislation: Creating a deductive system for changes in the experiment.