Chemistry

Solutions and substances in reactive bottles, including nitric acid and ammonium hydroxide, illuminated in different colors

Periodic table of modern chemical elements updated to 2016 by IUPAC.

Chemistry is the natural science that studies the composition, structure, and properties of matter, whether in the form of elements, species, compounds, mixtures, or other substances, as well as the changes they undergo during reactions and its relationship with chemical energy. Linus Pauling defined it as the science that studies substances, their structure (types and forms of arrangement of atoms), their properties and the reactions that transform them into other substances in reference over time. Chemistry, through one of its branches known as supramolecular chemistry, deals mainly with supra-atomic groups, such as gases, molecules, crystals and metals, studying their composition, statistical properties, transformations and reactions, although general chemistry also includes understanding the properties and interactions of matter on an atomic scale.

Chemistry is often called the "central science" because of its connecting role in the other natural sciences, relating to physics through physical chemistry, biology through biochemistry, astronomy through astrochemistry, geology via geochemistry, among others. Most chemical processes can be studied directly in the laboratory, using a number of often well-established techniques, both for handling materials and understanding the underlying processes. An alternative approach is provided by molecular modeling techniques, which draw conclusions from computational models.

Modern chemistry developed from alchemy, a protoscientific practice of an esoteric nature, but also experimental, that combined elements of chemistry, physics, biology, metallurgy, pharmaceuticals, among other disciplines. This phase ends with the chemical revolution, with the discovery of gases by Robert Boyle, the law of conservation of matter and the theory of combustion by oxygen postulated by the French scientist Antoine Lavoisier. The systematization became evident with the creation of the periodic table of elements and the introduction of atomic theory, as researchers developed a fundamental understanding of the states of matter, ions, chemical bonds, and chemical reactions. Since the first half of the 19th century, the development of chemistry has been accompanied by the appearance and expansion of a chemical industry of great relevance to the current economy and quality of life.

The disciplines of chemistry are grouped according to the class of subject matter under study or the type of study conducted. Among these are inorganic chemistry, which studies inorganic matter; organic chemistry, which studies organic matter; biochemistry, which studies the substances existing in biological organisms; physical chemistry, which understands the structural and energetic aspects of chemical systems at macroscopic, molecular and atomic scales, and analytical chemistry, which analyzes samples of matter and tries to understand their composition and structure through various studies and reactions.

Etymology

The word chemistry comes from the word «alchemy», the name of an ancient set of proto-scientific practices that encompassed various elements of modern science, as well as other widely varied disciplines such as metallurgy, astronomy, philosophy, mysticism or medicine. Alchemy, practiced at least since around the year 330, in addition to seeking the manufacture of gold, studied the composition of water, the nature of movement, growth, formation of bodies and their decomposition, the spiritual connection between bodies and spirits. An alchemist used to be called in everyday language "chemist", and later (officially, after the publication, in 1661, of the book The Skeptical Chemist, by the Irish chemist Robert Boyle) the art he practiced would be called chemistry.

In turn, alchemy derives from the Arabic word al-kīmīā (الکیمیاء). Originally, the term was a loan taken from the Greek, from the words χημία or χημεία (khemia and khemeia, respectively). The former could have Egyptian origin. Many believe that al-kīmīā derives from χημία, which in turn derives from the word Chemi or Kimi or Kham, which is the ancient name for Egypt in Egyptian. According to this hypothesis, khemeia could be "Egyptian art". The other alternative is that al-kīmīā derived from χημεία, meaning "to merge".. A third hypothesis, with more followers today, says that khemeia derives from the Greek khumos, the juice of a plant, and that it would come to mean " the art of juicing", and in this case "juice" could be a metal, and therefore could be "the art of metallurgy".

Definition

The definition of chemistry has changed over time; as new discoveries have been added to the functionality of this science. The term chemistry, according to the renowned scientist Robert Boyle, in 1661, was the area that studied the principles of mixed bodies.

In 1663, chemistry was defined as a scientific art through which one learns to dissolve bodies, obtain from them the different substances of their composition and how to unite them later to reach a higher level of perfection. This according to chemist Christopher Glaser.

The 1745 definition for the word chemistry, used by Georg Stahl, was the art of understanding the workings of mixtures, compounds, or bodies down to their basic principles, and then putting those bodies back together from those same principles.

In 1857, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. This definition would later evolve until, in 1947, it was defined as the science concerned with substances: their structure, their properties, and the reactions that transform them into other substances (characterization given by Linus Pauling).

More recently, in 1988, the definition of chemistry was broadened to be "the study of matter and the changes it involves", in the words of Professor Raymond Chang.

Introduction

The ubiquity of chemistry in the natural sciences makes it one of the basic sciences. Chemistry is of great importance in many fields of knowledge, such as materials science, biology, pharmacy, medicine, geology, engineering and astronomy, among others.

The natural processes studied by chemistry involve fundamental particles (electrons, protons, and neutrons), compound particles (atomic nuclei, atoms, and molecules), or microscopic structures such as crystals and surfaces.

From a microscopic point of view, the particles involved in a chemical reaction can be considered a closed system that exchanges energy with its surroundings. In exothermic processes, the system releases energy to its surroundings, while an endothermic process can only occur when the environment supplies energy to the reacting system. In most chemical reactions there is a flow of energy between the system and its field of influence, so the definition of a chemical reaction can be extended to include kinetic energy (heat) as a reactant or product.

Although there are a wide variety of branches of chemistry, the main divisions are:

• Biochemistry is a fundamental pillar of biotechnology, and it has been consolidated as an essential discipline to address the major current and future problems and diseases, such as climate change, shortages of agro-food resources in the face of rising global population, depletion of fossil fuel reserves, the emergence of new forms of allergies, increased cancer, genetic diseases, obesity, etc.
• Physical or physical chemistry, establishes and develops the fundamental physical principles behind the properties and behavior of chemical systems.
• Analytical chemistry, (from the Greek φναλσω) is the branch of chemistry that aims to study the chemical composition of a material or sample, through different laboratory methods. It is divided into quantitative analytical chemistry and qualitative analytical chemistry.
• Inorganic chemistry is responsible for the integrated study of the formation, composition, structure and chemical reactions of the inorganic elements and compounds (e.g. sulfuric acid or calcium carbonate); i.e. those that do not have carbon-hydrogen links, because they belong to the field of organic chemistry. Such separation is not always clear, for example in organometallic chemistry which is a overlap of both.
• Organic or chemical carbon chemistry is the branch of chemistry that studies a large class of carbon-containing molecules forming covalents carbon-carbon or carbon-hydrogen and other heteroatoms, also known as organic compounds. Friedrich Wöhler and Archibald Scott Couper are known as the parents of organic chemistry. The great importance of biological systems now makes much of the chemical work of a biochemical nature. Among the most interesting problems are, for example, the study of protein folding and the relationship between sequence, structure and protein function.
• Industrial Chemistry is responsible for the study of the manufacture of basic chemicals, the production and development of combinations that play an important role in technical development.

If there is an important and representative particle in chemistry, it is the electron. One of the greatest achievements of chemistry is having reached the understanding of the relationship between chemical reactivity and electronic distribution of atoms, molecules or solids. Chemists have taken the principles of quantum mechanics and its fundamental solutions for systems with few electrons and have made mathematical approximations for more complex systems. The idea of atomic and molecular orbital is a systematic way in which bond formation is understandable and is the sophistication of the initial Lewis dot models. The quantum nature of the electron makes the formation of bonds physically understandable and does not resort to beliefs like those used by chemists before the advent of quantum mechanics. Even so, great insight was gained from Lewis's point idea.

History

This section is an extract from History of Chemistry.[chuckles]edit]

Illustration of a chemical laboratory of the eighteenth century.

The history of chemistry covers a very wide period of time, ranging from prehistory to present, and is linked to the cultural development of humanity and its knowledge of nature. Ancient civilizations already used technologies that demonstrated their knowledge of the transformations of matter, and some would serve as the basis for the first studies of chemistry. These include the extraction of metals from their mines, the production of alloys such as bronze, the manufacture of ceramic red tissues, glazes and glass, fermentations of beer and wine, the extraction of plant substances to use them as medicines or perfumes and the transformation of fats into soap.

Neither philosophy nor alchemy, chemical protoscience, were able to truly explain the nature of matter and its transformations. However, based on experiments and recording their results, alchemists established the foundations for modern chemistry. The turning point towards modern chemistry occurred in 1661 with the work of Robert Boyle, The Sceptical Chymist: or Chymico-Physical Doubts & Paradoxes (The skeptical chemical: doubts and chemo-physical paradoxes), where the chemistry of alchemy is clearly separated, advocating for the introduction of the scientific method in chemical experiments. It is considered that chemistry reached the full range of science with the research of Antoine Lavoisier and his wife Marie Anne Pierrette Paulze, on which he based his law on the conservation of matter, among other discoveries that established the fundamental pillars of chemistry. From the centuryXVIII chemistry definitely acquires the characteristics of a modern experimental science. More precise measurement methods were developed that allowed better knowledge of phenomena and unproven beliefs were banished.

The history of chemistry is intertwined with the history of physics, as in atomic theory and in particular with thermodynamics, from the beginning with Lavoisier himself, and especially through the work of Willard Gibbs.

Epoch of the discovery of chemical elements
H																															He
Li	Be																									B	C	N	O	F	Ne
Na	Mg																									Al	Yeah.	P	S	Cl	Ar
K	Ca															Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Separate	Br	Kr
Rb	Mr.															And	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	You	I	Xe
Cs	Ba	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu	Hf	Ta	W	Re	You	Go	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	That's it.	Fm	Md	No.	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Nh	Fl	Mc	Lv	Ts	Og

Color key:Before 1500 (13 elements): Antiquity and the Middle Ages.1500-1800 (+21 elements): almost all in the Century of Lights.1800-1849 (+24 elements): scientific revolution and industrial revolution.1850-1899 (+26 elements): thanks to spectroscopy.1900-1949 (+13 elements): thanks to ancient quantum theory and quantum mechanics.1950-2000 (+17 elements): "postnuclear" elements (from no. 98 onwards) by bombing techniques.2001-presente (+4 elements): nuclear fusion.

Chemistry as a science

Robert Boyle

Under the influence of the new empirical methods proposed by sir Francis Bacon, Robert Boyle, Robert Hooke, John Mayow, among others, the old unscientific traditions began to be reshaped into a scientific discipline. Boyle, in particular, is regarded as the founding father of chemistry due to his most important work, "The Skeptical Chemist" which differentiates between the subjective claims of alchemy and the empirical scientific discoveries of the new chemistry. He he formulated Boyle's law, rejected the "four elements" and proposed a mechanical alternative to atoms and chemical reactions which could be subjected to rigorous experimentation, proved or disproved scientifically.

The theory of phlogiston (a substance that, they supposed, produced all combustion) was proposed by the German Georg Ernst Stahl in the 18th century and was only disproved towards the end of the century by the French chemist Antoine Lavoisier, who elucidated the principle of conservation of mass and developed a new system of chemical nomenclature used today.

Prior to Lavoisier's work, however, many important discoveries have been made, particularly regarding the nature of 'air', which was discovered to be composed of many different gases. Scottish chemist Joseph Black (the first experimental chemist) and Dutchman J. B. van Helmont discovered carbon dioxide, or what Black called "fixed air" in 1754; Henry Cavendish discovers hydrogen and elucidates its properties. Finally, Joseph Priestley and, independently, Carl Wilhelm Scheele isolate pure oxygen.

The English scientist John Dalton proposed the modern theory of atoms in 1803 in his book, The Atomic Theory, where he postulated that all substances are composed of "atoms" indivisible parts of matter and that different atoms have different atomic weights.

The development of the electrochemical theory of chemical combinations occurred in the early 19th century as the result of the work of two scientists in particular, J. J. Berzelius and Humphry Davy, thanks to the invention, not long ago, of the voltaic battery by Alessandro Volta. Davy discovered nine new elements, including the alkali metals, by extracting them from their oxides with electric current.

The British William Prout proposed ordering all elements by their atomic weight, since all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. J. A. R. Newlands devised a primitive table of the elements, which later became the modern periodic table created by the German Julius Lothar Meyer and the Russian Dmitri Mendeleev in 1860. Inert gases, later called noble gases, were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thus filling out the basic structure of the table.

Antoine Lavoisier

Organic chemistry has been developed by Justus von Liebig and others after Friedrich Wohler synthesized urea, showing that living organisms were, in theory, reducible to chemical terminology Other crucial advances of the century XIX were: the understanding of valence bonds (Edward Frankland,1852) and the application of thermodynamics to chemistry (J. W. Gibbs and Svante Arrhenius, 1870).

Chemical Structure

By the 20th century the theoretical foundations of chemistry were finally understood due to a series of discoveries that succeeded in Check the nature of the internal structure of atoms. In 1897, J. J. Thomson, from the University of Cambridge, discovered the electron and soon after the French scientist Becquerel, as well as the couple Pierre and Marie Curie investigated the phenomenon of radioactivity. In a series of scattering experiments, Ernest Rutherford, at the University of Manchester, discovered the internal structure of the atom and the existence of the proton, classifying and explaining the different types of radioactivity, and successfully transmutes the first element by bombarding it with nitrogen with alpha particles.

Rutherford's work on atomic structure was furthered by his students, Niels Bohr and Henry Moseley. The electronic theory of chemical bonds and molecular orbitals was developed by the American scientists Linus Pauling and Gilbert N. Lewis.

The year 2011 was declared by the United Nations as the International Year of Chemistry. This initiative was promoted by the International Union of Pure and Applied Chemistry, in conjunction with the United Nations Educational, Scientific and and the Culture.

Principles of Modern Chemistry

The current model of atomic structure is the quantum mechanical model. Traditional chemistry began with the study of elementary particles: atoms, molecules, substances, metals, crystals, and other aggregates of matter. Matter could be studied in liquid, gas, or solid states, either singly or in combination. The interactions, reactions, and transformations that are studied in chemistry are generally the result of interactions between atoms, giving rise to directions of the chemical bonds that hold them together with other atoms. Such behaviors are studied in a chemistry laboratory.

A variety of glassware materials are commonly used in the chemistry lab. However, glassware is not essential in chemical experimentation since a great deal of scientific experimentation (whether in applied or industrial chemistry) is done without it.

A chemical reaction is the transformation of some substances into one or more different substances. The basis of such a chemical transformation is the rearrangement of electrons in chemical bonds between atoms. It can be represented symbolically as a chemical equation, which usually involves atoms as the central particle. The number of atoms on the left and right in the equation for a chemical transformation must be equal (when unequal, the transformation, by definition, is not chemical, but rather a nuclear reaction or radioactive decay). The type of chemical reactions that a substance can undergo, and the energy changes that can accompany it, are determined by certain basic rules, known as chemical laws.

Energy and entropy considerations are important variables in almost all chemical studies. Chemical substances are classified on the basis of their structure, state, and chemical compositions. These can be analyzed using chemical analysis tools, such as spectroscopy and chromatography. Scientists engaged in chemical research are often referred to as "chemists". Most chemists specialize in one or more areas or subdisciplines. Several concepts are essential to the study of chemistry, and some of them are:

Matter

In chemistry, matter is everything that occupies space and has mass, shape, weight and volume, therefore it can be observed and measured. Matter is the substance that forms physical bodies, composed of particles. The particles that make up matter also have rest mass, however, not all particles have rest mass, an example is the photon. Matter can be a pure chemical substance or a mixture of substances.

Atoms

The atom is the basic unit of chemistry. It consists of a dense nucleus called the atomic nucleus, which is surrounded by a space called the "electron cloud". The nucleus is made up of positively charged protons and uncharged neutrons (both called nucleons). The electron cloud is negatively charged electrons revolving around the nucleus.

In a neutral atom, the negatively charged electrons balance the positive charge of the protons. The core is dense; The mass of a nucleon is 1,836 times that of an electron, yet the radius of an atom is approximately 10,000 times that of its nucleus.

The atom is the smallest entity that must be considered to preserve the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation states, coordination numbers, and the types of bonds an atom can hold. prefers to form (metallic, ionic, covalent, etc.).

Chemical Element

A chemical element is a pure substance that is made up of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, a number known as "atomic number" and which is represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in the nucleus. Although all the nuclei of all the atoms that belong to an element have the same atomic number, they do not necessarily have to have the same mass number; Atoms of an element that have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are carbon atoms, but carbon atoms can have mass numbers of 12 or 13.

From the moment the first elements were discovered, attempts were made to order or classify them in order to study their properties or characteristics.

The standard presentation of the chemical elements is in the periodic table, which orders the elements by atomic number. The periodic table is organized into groups (also called columns) and periods (or rows). The periodic table is useful for identifying periodic trends.

Chemical compound

Structural formula of the caffeine molecule.

A chemical compound is a pure chemical substance made up of more than one element. The properties of a compound bear little similarity to those of its elements. The standard nomenclature for compounds is set by the International Union of Pure and Applied Chemistry (IUPAC). Organic compounds are named according to the organic naming system. Inorganic compounds are named according to the inorganic naming system. In addition, the Chemical Abstracts Service has devised a method for naming chemical substances. In this scheme each chemical substance is identifiable by a number known as a CAS registry number.

Subdisciplines of Chemistry

Institute of Inorganic Chemistry and Environmental Engineering, Polymer Institute and Institute of Organic Chemistry Technology, Technological University of Western Pomerania, in Estetino, Poland.

Chemistry covers a fairly broad field of study, so in practice each topic is studied in a particular way. The six main and most studied branches of chemistry are:

• Inorganic chemistry: synthesis and study of electrical, magnetic and optical properties of compounds formed by non-carbon atoms (although with some exceptions). It treats especially new compounds with transition metals, acids and bases, among other compounds.
• Organic chemistry: Synthesis and study of compounds that are based on carbon chains.
• Biochemistry: studies chemical reactions in living beings, studies organism and living beings. Biochemistry is the study of chemicals, chemical reactions and chemical interactions taking place in living organisms. Biochemistry and organic chemistry are closely related, such as medical or neurochemical chemistry. Biochemistry is also associated with molecular biology and genetics.
• Physical chemistry: also known as physicochemistry, studies the physical foundations and bases of chemical systems and processes. In particular, the energy and dynamic aspects of such systems and processes are of interest to the physical chemical. Among its most important areas of study are chemical thermodynamics, chemical kinetics, electrochemicals, statistical mechanics and spectroscopy. It is usually associated with quantum chemistry and theoretical chemistry.
• Industrial chemistry: Study the methods of production of chemical reagents in high amounts, in the most economically beneficial way. At present it also seeks to combine its initial interests, with a low environmental damage.
• Analytical chemistry: studies the methods of detection (identification) and quantification (determination) of a substance in a sample. Subdivide in Quantitative and Qualitative.^{[chuckles]required]}

The difference between organic chemistry and biological chemistry is that in biological chemistry DNA molecules have a history and, therefore, in their structure they tell us about their history, about the past in which they have been constituted, while that an organic molecule, created today, is only a witness of its present, without past and without historical evolution.

In addition, there are multiple subdisciplines that, because they are too specific or multidisciplinary, are studied individually:^{[citation required]}

• Astrochemistry is the science that deals with the study of the chemical composition of the stars and the diffuse material found in interstellar space, usually concentrated in large molecular clouds.
• Electrochemical is a branch of chemistry that studies the transformation between electrical energy and chemical energy.
• Photochemistry, a subdisciplinary chemical, is the study of interactions between atoms, small molecules, and light (or electromagnetic radiation).
• Magnetochemical is the branch of chemistry that is dedicated to the synthesis and study of the substances of interesting magnetic properties.
• Nanochemical (related to nanotechnology).
• Petrochemical is the industry that uses oil or natural gas as raw materials for the production of chemicals.
• Geochemistry: studies all the transformations of the minerals existing on earth.
• Computational chemistry is a branch of chemistry that uses computers to help solve chemical problems. It uses the results of theoretical chemistry, incorporated into some software to calculate the structures and properties of molecules and solid bodies. While their results normally complement information obtained in chemical experiments, they may, in some cases, predict non-observed chemical phenomena to date.
• Quantum chemistry is a branch of theoretical chemistry where quantum mechanics and quantum field theory apply.
• Macromolecular chemistry: studies the preparation, characterization, properties and applications of macromolecules or polymers;
• Environmental chemistry: studies the influence of all chemical components on the earth, both in their natural and anthropogenic form;
• Nuclear chemical or nuclear physics is a branch of physics that studies the properties and behavior of atomic nuclei.
• Organometallic chemistry is responsible for the study of organometallic compounds, which are those chemical compounds that have a link between a carbon atom and a metallic atom, its synthesis and its reactivity.
• supramolecular chemistry is the branch of chemistry that studies supramolecular interactions, that is, between molecules.
• Theoretical chemistry includes the use of mathematics and physics to explain or predict chemical phenomena.
• Toxic chemistry: studies the toxicity of natural or artificial chemicals on the environment and the ecosystem, including the human being, in the short and long term.

The contributions of famous authors

About 455 years ago only twelve elements were known. As more elements were discovered, scientists realized that they were all in a precise order. When they put them in a table arranged in rows and columns, they found that the elements in the same column had similar properties. But there were also empty spaces in the table for the still unknown elements. These hollow spaces led the Russian scientist Dmitri Mendeleev to predict the existence of germanium, with atomic number 32, as well as its color, weight, density and melting point. His "prediction about other elements such as gallium and scandium was also very accurate," says Chemistry, a chemistry textbook published in 1995.

Relevant chemists of the 20th-21st century, winners of the Nobel Prize in Chemistry

Marie Curie discovered the Polonio and the radio.

Many scientists have contributed to the growth of Chemistry through important discoveries that have earned them the Nobel Prize in Chemistry. By way of example, among many of them, we can mention Emil Fischer who discovered the synthesis of glucose and other sugars, Maria Curie for her studies in the field of radioactivity discovering radium and polonium. Theodor Svedberg, for the invention and application of the ultracentrifuge; Irene Curie, daughter of Maria Curie, for building the first nuclear reactor using controlled nuclear fission. Otto Hanh for his discovery of nuclear fission, Linus Pauling for his study of the atomic structure of proteins, and sickle cell disease caused by a genetic defect in the production of hemoglobin. Luis Federico Leloir for the discovery of the chemical processes that give rise to the formation of sugars in plants, Paul Crutzen shared the Nobel Prize with Mario Molina and Sherwood Rowlands for the discovery of the role of nitrogen oxides and fluorocarbons in the destruction of the ozone layer, Roger David Kornberg for discovering how cells copy genetic information. The last scientists who have obtained the Nobel Prize in Chemistry have been Stanley Whittingham and Akira Yoshino for the development of lithium-ion batteries.

See also: News on the peaceful use of radioactivity

Field of study: the atom

The origin of the atomic theory dates back to the philosophical school of the atomists, in ancient Greece. The empirical foundations of the atomic theory, in accordance with the scientific method, is due to a set of works carried out by Antoine Lavoisier, Louis Proust, Jeremias Benjamin Richter, John Dalton, Gay-Lussac, Berzelius and Amadeo Avogadro, around the beginning of the century. XIX.

Atoms are the smallest fraction of matter studied by chemistry, they are made up of different particles, electrically charged, electrons, negatively charged; protons, positively charged; neutrons, which, as their name suggests, are neutral (no charge); they all contribute mass to contribute to the weight.

The types of atoms that make up cells are relatively few:

Each atom has in its central part a dense positively charged nucleus surrounded at some distance by a cloud of negatively charged electrons that are held in orbit around the nucleus by electrostatic attraction. The nucleus is made up of two types of subatomic particles: protons, which are positively charged, and neutrons, which are electrically neutral. The number of protons present in the nucleus of the atom determines its atomic number. A hydrogen atom has a single proton in the nucleus; therefore hydrogen, whose atomic number is 1, is the lightest element. The electric charge of a proton is exactly equal and opposite to the charge of an electron. The atom is electrically neutral; the number of negatively charged electrons around the nucleus is equal to the number of positively charged protons inside the nucleus; therefore, the number of electrons in an atom is also equal to the atomic number. All atoms of an element have the same atomic number.

Fundamental concepts

Particles

Atoms are the smallest parts of an element (such as carbon, iron, or oxygen). All the atoms of the same element have the same electronic structure (responsible for most of the chemical characteristics), and may differ in the number of neutrons (isotopes). Molecules are the smallest parts of a substance (such as sugar), and are made up of atoms linked together. If they have an electrical charge, both atoms and molecules are called ions: cations if they are positive, anions if they are negative.

The mol is used as a unit counter, like the dozen (12) or the thousand (1000), and is equivalent to 6,022045⋅ ⋅ 1023{displaystyle 6,022045cdot 10^{23}. It is said that 12 grams of carbon or a gram of hydrogen or 56 grams of iron contain approximately one mol of atoms (the molar mass of an element is based on the mass of a mol of that element). It is said then that the mol is a unit of change. The mol is directly related to the Avogadro number. The number of Avogadro was estimated for the carbon atom by the Italian chemical and physicist Carlo Amedeo Avogadro, Count of Quarequa and di Cerreto. This value, shown above, is equivalent to the number of particles present in 1 mol of that substance:

1 glucose mol 6,022045⋅ ⋅ 1023{displaystyle 6,022045cdot 10^{23} Glucose molecules. 1 uranium mill equivalent to 6,022045⋅ ⋅ 1023{displaystyle 6,022045cdot 10^{23} uranium atoms.

Within atoms there can be an atomic nucleus and one or more electrons. Electrons are very important to chemical properties and reactions. Inside the nucleus are neutrons and protons. Electrons are found around the nucleus. It is also said that the atom is the basic unit of matter with its own characteristics. It is formed by a nucleus, where the protons are found.

From atoms to molecules

Bonds are the unions between atoms to form molecules. Whenever a molecule exists, it is because it is more stable than the atoms that form it separately. The difference in energy between these two states is called the binding energy.

Atoms combine in fixed proportions to make specific molecules. For example, two hydrogen atoms combine with one oxygen to make a water molecule. This fixed ratio is known as stoichiometry. However, the same number and type of atoms can combine in different ways giving rise to isomeric substances.

Orbitals

Space diagram showing the atom hydrogenoid orbitals of angular time of type d (l=2).

For a detailed description and understanding of chemical reactions and the physical properties of different substances, their description through orbitals, with the help of quantum chemistry, is very useful.

An atomic orbital is a mathematical function that describes the arrangement of one or two electrons in an atom. A molecular orbital is the analog in molecules.

In the molecular orbital theory, the formation of the covalent bond is due to a mathematical combination of atomic orbitals (wave functions) that form molecular orbitals, so called because they belong to the whole molecule and not to an individual atom. Just as an atomic orbital (whether hybrid or not) describes a region of space around an atom where an electron is likely to be found, a molecular orbital also describes a region of space in a molecule where electrons are most likely to be found. electrons.

Like an atomic orbital, a molecular orbital has a specific size, shape, and energy. For example, in the molecular hydrogen molecule, two atomic orbitals are combined, each one occupied by an electron. There are two ways in which orbital combining can occur: additive and subtractive. The additive combination leads to the formation of a molecular orbital that has lower energy and has an almost oval shape, while the subtractive combination leads to the formation of a molecular orbital with higher energy and that generates a node between the nuclei.

From orbitals to substances

Orbitals are mathematical functions to describe physical processes: an orbital only exists in the mathematical sense, as a sum, a parabola or a square root can. Atoms and molecules are also idealizations and simplifications: an atom and a molecule only exist in a vacuum, and in a strict sense a molecule only breaks down into atoms if all its bonds are broken.

In the "real world" only materials and substances exist. If real objects are confused with the theoretical models used to describe them, it is easy to fall into logical fallacies.

Dissolutions

In water, and in other solvents (such as acetone or alcohol), it is possible to dissolve substances, so that they remain disintegrated into the molecules or ions that compose them (the solutions are transparent). When a certain limit, called solubility, is exceeded, the substance no longer dissolves, and remains either as a precipitate at the bottom of the container, or as a suspension, floating in small particles (suspensions are opaque or translucent).

Water, universal solvent

Concentration is the measure of the amount of solute per unit amount of solvent.

Measure of concentration

The concentration of a solution can be expressed in different ways, depending on the unit used to determine the amounts of solute and solvent. The most common are:

• g/l (grams per litre) reason solute/disolvent or solute/dissolution, depending on the convention
• % p/p (percent concentration in weight) reason solute/dissolution
• % V/V (percent concentration in volume) ratio solute/dissolution
• M (molarity) reason solute/dissolution
• N (normality) reason solute/dissolution
• m (molality) reason soluto/disolvente
• x (moulding)
• ppm (parts per million) reason solute/dissolution

Acidity

pH is a logarithmic scale to describe the acidity of an aqueous solution. Acids, such as lemon juice and vinegar, have a low pH (below 7). Bases, such as soda or sodium bicarbonate, have a high pH (greater than 7).

pH is calculated using the following equation:

pH=− − log aH+≈ ≈ − − log [chuckles]H+]{displaystyle pH=-log a_{H^{+}}approx -log[H^{+}],}

where aH+{displaystyle a_{H^{+},} is the activity of hydrogen ions in the solution, which in diluted solutions is numerically equal to the molarity of hydrogen ions [chuckles]H+]{displaystyle [H^{+},} that yields the acid to the solution.

• a neutral solution (extra pure water) has a pH of 7, which implies a concentration of hydrogen ions of 10^-7 M;
• 

  pHmeter_ pH meter
  an acid solution (e.g. sulfuric acid) has a pH ≤7, i.e., the concentration of hydrogen ions is greater than 10^-7 M;
• a basic solution (e.g. potassium hydroxide) has a pH  7, i.e. the concentration of hydrogen ions is less than 10^-7 M.

Formulation and nomenclature

IUPAC, an international body, maintains rules for chemical formulation and nomenclature. This body is the universally recognized authority on chemical nomenclature and terminology. In this way, it is possible to refer to chemical compounds in a systematic and unequivocal way.

By using chemical formulas it is also possible to systematically express chemical reactions, in the form of a chemical equation.

For example:

MgSO4+Ca(OH)2 CaSO4+Mg(OH)2{displaystyle MgSO_{4}+Ca(OH)_{2}rightleftharpoons CaSO_{4}+Mg(OH)_{2}}}}