High School Chemistry/Chemistry in History

During medieval times, a group of people known as alchemists began looking for ways to transform common metals, such as lead, copper and iron, into gold (Figure 1.14). Can you imagine how much money you would make if you could go to the store, buy some iron nails, and turn them into gold? You’d be rich in no time!



Alchemists experimented with many different kinds of chemicals, searching for what they termed the "philosopher's stone" – a legendary substance that was necessary for the transformation of common metals into gold. We now know that there is no such thing as a "philosopher's stone", nor is there any chemical reaction that creates gold from another metal. We know this because we now have a much better understanding of the matter in our universe. Nevertheless, it was thanks to those early alchemists that people became interested in chemistry in the first place.

Lesson Objectives

 * Give a brief history of how chemistry began.
 * State the Law of Conservation of Mass.
 * Explain the concept of a model, and create simple models from observations.

"Chemistry" was Derived from an Arabic Word
When we speak of "chemistry", we refer to the modern, scientific study of matter and the changes that it undergoes. Still, it’s no coincidence that the word "chemistry", looks a lot like the word "alchemy". Early alchemists were commonly known as 'chemists', and over time, people started referring to their work, particularly the more legitimate forms of it, as chemistry. In many ways, it’s appropriate that our word for the present-day study of matter comes from the early practice of alchemy because a lot of the techniques and equipment fundamental to modern chemistry were actually developed by early alchemists.

The origin of the word "alchemy" is something of a mystery. Certainly, early Europeans borrowed "alchemy" from the Arabic word "al-kimia", meaning "the art of transformation" (of course, the transformation that alchemists were primarily concerned with involved the creation of gold). Most of what we know today about early alchemy is based on translations of Arabic documents. That’s because Muslim alchemists were some of the first to keep careful notes about their experiments.

Even though our earliest records of alchemy come from the Arab Empire, some scholars believe that Arabs adopted alchemy and the word "al-kimia" from the Greeks around 650 AD. The Greeks, in turn, may have learned of alchemy from the Egyptians. Khem was an ancient name for Egypt, and Egyptians were known, in early history, as masters of the art of working with gold. It's very likely that "al-kimia" is actually a distorted version of the word "al-kimiya" meaning "the art of the land of Khem", or the art of Egypt.

The Origins of Chemistry were Multicultural


While the word "chemistry" may have its roots in Egypt, chemical experimentation seems to have been prevalent all over the world, even as early as the 5th century BC. In China, the goal of the early alchemists was largely to find "the elixir of life" – a potion that could cure all diseases and prevent death. Ironically, many of these early elixirs involved mixtures of mercury and arsenic salts, both of which are extremely poisonous. In fact, it's rumored that several Chinese emperors actually died after drinking "elixirs of life" (Figure 1.15). Despite never finding a magical potion that could cure all diseases, early Chinese chemists did discover many new chemicals and chemical reactions, including those used in fireworks and gunpowder.

Like the Chinese, alchemists from India were interested in some of the medical benefits of different chemicals. In addition to medicine, Indian alchemists were fascinated by metals and metallurgy. Early Indian writings contain methods for extracting and purifying metals like silver, gold and tin from ores that were mined out of the ground. Moreover, it was alchemists from the Indian subcontinent who first realized that by mixing molten metals with other chemicals they could produce materials that had new and beneficial properties. For example, Wootz steel (also known as Damascus steel) was a substance discovered in Sri Lanka around 300 AD. It was made by mixing just the right amounts of molten iron, glass and charcoal, but it became famous because it could be used to produce swords, legendary for their sharpness and strength in battle.

Around the same time that Wootz steel was being developed in Sri Lanka, Egyptian and Greek alchemists were beginning to experiment as well. Much of the alchemy in this part of the world involved work with colors and dyes and, of course, the transformation of common metals into gold and silver. Greek philosophers like Plato and Aristotle, however, were also responsible for the important suggestion that the universe could be explained by unified natural laws. As you will discover in the next section, modern chemistry relies on the study of these universal laws. Of course, modern scientific laws are slightly different than the laws that either Plato or Aristotle had in mind. In general, scientific laws are determined by careful experimentation and observation, whereas the early Greeks believed that their "natural laws" could be deduced through philosophy.

Medieval Europeans were similarly fascinated by alchemy. Unfortunately, many alchemists in Europe borrowed ideas from the more mystical of the Arabian alchemists and, as a result, European alchemy quickly became associated with wizardry, magic, and the search for the "philosopher's stone". It wasn’t until the late 17th century that European chemists began applying the scientific method. Robert Boyle (1627 – 1691) was the first European to do so, using quantitative experiments to measure the relationship between the pressure and the volume of a gas. His use of the scientific method paved the way for other European scientists and helped to establish the modern science of chemistry.



About 100 years after Robert Boyle first performed his experiments, a French scientist by the name of Antoine Lavoisier (1743 - 1794) employed the scientific method when he carefully measured the masses of reactants and products before and after chemical reactions (Figure 1.16). Since the total mass (or quantity of material) never changed, Lavoisier's experiments led him to the conclusion that mass is neither created nor destroyed. This is known as the Law of Conservation of Mass. Lavoisier is often called “The Father of Modern Chemistry” because of his important contribution to the study of matter.

After the success of Lavoisier's work, experiments involving careful measurement and observation became increasingly popular, leading to a rapid improvement in our understanding of chemicals and chemical changes. In fact, by the end of the 19th century, chemical knowledge had increased so much that practically everyone had stopped searching for the "philosopher's stone".

What Chemists Do
You might wonder why the study of chemistry is so important if you can't use it to turn iron into gold or to develop a potion that will make you immortal. Why didn't chemistry die when scientists like Boyle and Lavoisier proved alchemy was nothing but a hoax? Well, even though we can't use chemistry to make gold or to live forever, modern chemistry is still very powerful! There may be no such thing as a potion that cures all diseases, but many chemists today are developing cures for specific diseases. In fact, chemists are working on everything from treatments for HIV/AIDS to medications for fighting cancer.

Modern chemists study not only chemicals that can help us, but also chemicals that can hurt us. For example, environmental chemists test the air, soil, and water in our neighborhoods to make sure that we aren't exposed to heavy metals (such as mercury or lead) or chemical pesticides. Moreover, when environmental chemists do find dangerous substances, they use their knowledge of chemistry to clean up the contamination. Similarly, every time you buy packaged food from the grocery store, you can be sure that many tests have been done by chemists to make sure that those foods don’t contain any toxins or carcinogens (cancer-causing chemicals).

Chemists are also responsible for creating many important materials we use today. Other technologies rely on chemistry as well. In fact, your flat-screen LCD TV, the cubic zirconium ring on your finger, and the energy efficient LED lights in your home are all thanks to our improved understanding of chemistry (Figure 1.17).



So, how do chemists accomplish all of these remarkable achievements? Unlike many of the early alchemists that experimented by randomly mixing together anything that they could find, today's chemists use the scientific method. This means that chemists rely on both careful observation and well-known physical laws. By putting observations and laws together, chemists develop what they term models. Models are really just ways of predicting what will happen given a certain set of circumstances. Sometimes these models are mathematical, but other times, they are purely descriptive.

A model is any simulation, substitute, or stand-in for what you are actually studying. A good model contains the essential variables that you are concerned with in the real system, explains all the observations on the real system, and is as simple as possible. A model may be as uncomplicated as a sphere representing the earth or billiard balls representing gaseous molecules, or as complex as mathematical equations representing light.

The learner.org website allows users to view streaming videos of the Annenberg series of chemistry videos. You are required to register before you can watch the videos but there is no charge. After you register the first time, you can return to the website (from the same computer) and view videos without registering again. The website has a video that applies to this lesson. The video is called "Modeling The Unseen". Video on Demand – Modeling the Unseen.

Over time, scientists have used many different models to represent atoms. As our knowledge of the atom changed, so did the models we use for them. Our model of the atom has progressed from an "indestructible sphere", to a dish of "plum pudding", to a "nuclear model".

Hypotheses and theories comprise some ideas that scientists have about how nature works but of which they are not completely sure. These hypothesis and theories are models of nature used for explaining and testing scientific ideas.

Chemists make up models about what happens when different chemicals are mixed together, or heated up, or cooled down, or compressed. Chemists invent these models using many observations from experiments in the past, and they use these models to predict what might happen during experiments in the future. Once chemists have models that predict the outcome of experiments reasonably well, those working models can help to tell them what they need to do to achieve a certain desired result. That result might be the production of an especially strong plastic, or it might be the detection of a toxin when it's present in your food.

Science is not the only profession whose members make use of the scientific method. The process of making observations, suggesting hypotheses, and testing the hypotheses by experiment is also a common procedure for detectives and physicians.

Lesson Summary

 * The word "chemistry" comes from the Arabic word "al-kimia" meaning "the art of transformation".
 * Chemistry began as the study of alchemy. Most alchemists were searching for the "philosopher's stone", a fabled substance that could turn common metals into gold.
 * Chinese alchemists were particularly interested in finding "the elixir of life".
 * In India, much early chemistry focused on metals.
 * The scientific method involves making careful observations and measurements and then using these measurements to propose hypotheses (ideas) that can, in turn, be tested with more experiments.
 * Robert Boyle and Antoine Lavoisier employed the "scientific method", thereby bringing about the rise of modern chemistry.
 * The Law of Conservation of Mass states that mass is neither created nor destroyed.
 * Modern chemists perform experiments and use their observations to develop models. Models then help chemists to understand and predict the results of future experiments. Models also help chemists to design new materials and cures for diseases.

Review Questions

 * 1) Where does the word "chemistry" come from?
 * 2) Consider the following data about John's study habits, and grades:
 * (a) Propose a qualitative (words, but no math) model that might describe how the length of time John spends studying relates to how well he does on the test?
 * (b) If John wants to earn 92% on his next test, should he study for about 6 hours, 9 hours, 12 hours, or 18 hours? Justify your answer.
 * (c) If John studies for 7 hours, do you think he will score 15%, 97%, 68%, or 48%? Justify your answer.
 * 1) Helen wanted to know if lemon juice chemically reacts with tea to lighten its color. So Helen added 25 drops of lemon juice to 250 mL of tea and observed that the tea colored lightened significantly. Helen wanted to make sure that the color lightening was the result of a chemical reaction and not the result of dilution. Which one of the following activities should Helen carry out to serve as a control for this experiment?
 * (a) Helen should add 25 drops of orange juice to another 250 mL sample of tea.
 * (b) Helen should add 25 drops of distilled water to another 250 mL sample of tea.
 * (c) Helen should add 25 drops of lemon juice to a 250 mL sample of distilled water.
 * (d) Helen should add 25 drops of tea to a 250 mL sample of lemon juice.
 * (e) Helen should add 25 drops of tea to a 250 mL sample of tea.
 * (e) Helen should add 25 drops of tea to a 250 mL sample of tea.

Vocabulary

 * chemistry
 * The science of the composition, structure, properties, and reactions of matter


 * hypothesis
 * A proposal intended to explain a set of observations.


 * law
 * A relationship that exists between specific observations.


 * scientific method
 * A method of investigation involving observation to generate and test hypotheses and theories.


 * theory
 * A hypothesis that has been supported with repeated testing.