Preferencia Electoral

In the course of its development, chemistry, like any other science, has undergone a number of stages. Each stage has led to a better understanding of phenomena that are studied by chemistry. Chemistry involves the structure of substances, their properties and transformation. Indeed, chemists have always been interested in the kinds of particles that substances are made of, which properties of these particles define the various substances that surround us and which of them define those transformations of chemical substances that we observe in nature and in experiments.

Everything that surrounds us is made up of substances, and the properties of various substances are different. For example, things made of the substances called wood and cotton can burn, while things made of metal cannot. Indeed, there are ever so many different substances: wood, metals, gasoline, water, gas, etc.

Properties of substances are diverse as far as color, solidity, electrical conductivity, are concerned. Also, substances can enter various processes of chemical transformation, as a result of which we get new substances. For example, gasoline, a fluid, turns into carbon dioxide (CO2)

and water (H2O) when it burns inside a motor. Methane, a gas used in gas stoves for cooking, as

a result of several chemical transformations performed at large chemical plants, is transformed into chemical fertilizer.

Chemistry answers such questions as How are substances constructed? Why do substances differ

from each other? How does the transformation of substances take place?

Chemistry, like physics, is a fundamental science. However, physics includes the study of energy and force, while chemistry mainly studies substances and their transformations.

General chemistry studies the fundamentals necessary for understanding organic, inorganic, physical and biological chemistry and for the comprehension of science as a whole.

General chemistry is among those subjects that educated people cannot do without. Indeed, a person ignorant of chemistry, would be out of touch with modern society; he would be unable to take part in an ordinary conversation in the 21st century!

A person without basic knowledge of chemistry is unable to understand the notes on labels that accompany foods. He cannot take part in conversations that occur in our modern society concerning such important matters as chemical weapons, narcotics, smoking and alcoholism. Such a person cannot understand the differences in the brands of gasoline at the filling stations, why cholesterol can be harmful, which detergents are dangerous and why, as well as a variety of other topics.

People in professions directly connected with chemistry (nuclear fission chemists, pharmacists, chemist-analysts) are included in lists of the top ten most prestigious and well-paid professions. Without knowledge of chemistry, one cannot become a doctor, a judge, a lawyer or a businessman. Prosecutors and counsels for defense call upon almost every American citizen to serve his country in the capacity of a juror, where he must understand the various proofs offered by the prosecutors or the lawyers. Indeed, the bases of many proofs lie in knowledge of chemical analyses.

What does it mean to know chemistry? This means: to understand the physical sense of chemical

phenomena. Physical sense includes the explanations of chemical phenomena arising from the

knowledge of physics and mathematics already learned in high school. Thus, in order to ease assimilation to the topic when studying chemistry, students should review physics and mathematics.

When studying general chemistry, students learn about the structure of the smallest particle of a substance — the atom. They learn about the various properties of atoms, they define the substances of things surrounding us and they learn how chemical and physical transformations of substances take place and how the structure of substances defines their physical and chemical properties.

Depth of knowledge

Having arrived in America from Russia in 1991, the elder of the two authors of this book was accustomed to go for a walk with his nine-year-old granddaughter. The girl would converse with her granddad about her new friends and about her acquired knowledge of English, while the elder, in turn, would share his knowledge of natural sciences. Once he told the girl a bit about atom structure.

Six years passed. The granddaughter came home from school one day — extremely upset. She said that the teacher had asked the class "Who knows what an atom is?" To her surprise, almost all the kids raised their hands. So did she, for this was a chance to boast of her knowledge in chemistry. She thought she would be the only one to properly answer that question. Who else had such a smart chemist grandfather as she did?

First, to calm the girl, the grandfather explained that the phrase "I know what the atom is" is illogical. On the one hand, it amounts to nothing; on the other hand, it can signify knowledge of various depths. Now what do we mean by the depth of knowledge?

Let's answer this question relative to the atom and the molecule. This question will cause many students to raise their hands:

1) those who know that atoms are tiny particles;

2) those who know what kind of particles atoms are made of; 3) those who know how atoms are formed;

4) those who know how atoms form molecules;

5) those who know what forces bind atoms into molecules; 6) those who know how to calculate the bonding energy;

7) those who know how the atoms' properties define the molecules' properties; 8) those who know what physical laws deal with atom and molecule structure; As we see, knowledge about the atom differs in depth.

Indeed, in the process of explaining the chemical phenomena of the atom, the molecule, chemical bonding, the structure of chemical substances, chemical reactions, the physical and chemical properties of substances and related topics, we will deepen our knowledge of chemistry. That is, we will answer the question:

Why is it that a simple description of atom and molecule structure precedes the section of the book devoted to a historic view, where various experiments and theoretical proofs are demonstrated to show how atom and molecule structure were established?

The world-famous scientist, Richard Feynman, who won the Nobel Prize for Physics, asked: "What is the shortest phrase, concerning the most important scientific knowledge we possess, that you would pass on to the next generation?" Feynman answered himself: "Everything is made

of atoms."

It is a known fact that all the substances around us (iron, stone, salt, bread, liquids, etc.) consist of molecules, which are the smallest particle of substances and consist of atoms. An atom consists of a positively charged nucleus around which negatively charged electrons rotate. A nucleus consists of nucleons (protons and neutrons).

Protons are always positively charged, their charges (in absolute units) being equal to those of the electrons.

Neutrons do not carry any electrical charges. Protons and neutrons consist of quarks.

There are 6.02 · 1023_{molecules of water in 18 grams of water. A molecule of water consists of} an atom of oxygen (O) and two atoms of hydrogen (H), i.e., H2O.

A hydrogen atom consists of a nucleus and one electron.

To break up water into molecules, we must heat the water to a temperature of 100° C. To further break up a water molecule into atoms, we must heat the steam to a temperature of about 5,000° C.

To tear away the electrons of the oxygen atom from its nucleus, we must raise the temperature to more than 10,000° C.

Thus, according to experimental data, the limit for breaking up particles into the smallest units possible depends on the temperature (energy) that we use in order to break up the substance. Now let's see how the atom is constructed.