Chemical elements

Atoms

Atoms are material objects with a certain mass, size, composition, nucleus charge, and electron shell structure. They are preserved during chemical reactions, meaning they are chemically indivisible and only break down in nuclear transformations.

Atoms with the same nucleus charge belong to a specific chemical element and are carriers of its chemical properties.

Chemical Elements

Chemical element refers to a type of atoms with the same nucleus charge. Chemical elements are components of over 10 million organic and hundreds of thousands of inorganic substances. New compounds formed in chemical reactions consist of the same atoms as the original ones.

Currently, 110 chemical elements are known, arranged in the periodic table of elements by D. I. Mendeleev according to certain rules. Of these, 88 have been identified in nature, while 22 have been artificially synthesized through nuclear transformations.

Depending on their properties, origin, and occurrence in nature, chemical elements are classified into the following groups:

• By origin. Chemical elements are classified into natural and artificial by origin. The former exist in various natural compounds, while the latter are produced through nuclear reactions. Artificial elements generally have atomic numbers above 94 (Am, Cm, Bk, etc.).
• By chemical properties. Chemical elements are distinguished into metals and nonmetals by their chemical properties, which are further divided into families: alkali metals (Li, Na, K, Rb, Cs, Fr), alkaline earth metals (Cu, Sr, Ba, Ra), Iron family (Fe, Co, Ni), Platinum group metals (Ru, Rh, Pd, Os, Ir, Pr), halogens (F, Cl, Br, I), chalcogens (S, Se, Te).
• By structure. Based on the structure of the outer energy level and similar chemical properties, elements are divided into four blocks: s-elements (main group elements I, II), p-elements (main group elements III-VIII), d-elements (side group elements I-VIII), and f-elements (lanthanides and actinides).
• By occurrence. Elements in the Earth's crust are classified into abundant and rare. The abundant elements include Oxygen (49% by mass), Silicon (29.5%), Aluminum (8.05%), Iron, Calcium, Sodium, Potassium, and Magnesium. Together, these elements constitute 98.53% of the Earth's crust by mass, with the remaining 1.47% comprising all other elements.

  Rare or scattered elements are those less commonly found in nature, such as gallium, rubidium, thallium, lanthanum, etc.
• Radioactive elements. A separate group comprises radioactive elements (Tc, Pm, Po, At, etc.), whose atomic nuclei are unstable and capable of spontaneous decay.
• By importance for organisms. Chemical elements are divided into organogenic and biogenic based on their importance for humans and animals. These elements are the most important chemical components of various living organisms' systems.
• By physiological effect. Elements' physiological effects on living organisms classify them as essential, neutral, or toxic. Elements constantly present in the organism are termed essential. Toxic elements disrupt the organism's functions when present in excessive amounts. Examples include Arsenic (As), Lead (Pb), Mercury (Hg), Cadmium (Cd), Thallium (Tl), Barium (Ba), etc.

  However, it's worth noting that even elevated doses of some essential elements can lead to poisoning in humans and animals.

In some cases, a chemical element and a simple substance are represented by the same symbol, but these concepts should not be equated.

Substances

Substance is a form of existence of chemical elements in a free or combined state. Substances are classified into simple substances (hydrogen, oxygen, ozone, copper, silver, iron Fe) and complex substances, such as water, hydrogen peroxide, phosphoric acid, methanol, glucose, etc.

As early as 1741, M. Lomonosov hypothesized the existence of two types of particles in substances: elements (atoms) and corpuscles (molecules). According to Lomonosov's hypothesis, elements are particles of matter that do not consist of any other bodies, while corpuscles are aggregations of elements into one small mass.

Later, English chemist J. Dalton experimentally confirmed the atomic theory by formulating the law of multiple proportions in 1803, while A. Avogadro introduced the concept of a molecule as the smallest particle of matter composed of atoms.

In 1811, he formulated a law known as Avogadro's law: equal volumes of different gases at the same conditions contain the same number of molecules. This demonstrated that molecules can consist of atoms of a single element (simple substance) as well as atoms of different elements (complex substance).

It is now known that simple substances can be molecular — composed of molecules (O₂, H₂, O₃, Cl₂, N₂, etc.) and non-molecular — those consisting solely of atoms, such as noble gases (Ne, Ar, Kr), graphite, diamond, sulfur, and others.

Some simple substances can exist in the form of two or more substances with different properties. This phenomenon is called allotropy, and simple substances formed by one element are called allotropic modifications of that element.

Examples of oxygen allotropic modifications include oxygen O₂ and ozone O₃, while carbon has allotropes like diamond, graphite, carbine, and fullerene (buckyball). The differences in their properties are due to the different number of atoms in the molecules or different crystalline structures (polymorphism).

For the names of simple substances according to the new nomenclature, their traditional writing remains, for example: copper, iron, mercury, hydrogen, nitrogen, etc. This also applies to terms derived from these words: hydrogen electrode, iron nail, copper plate, mercury thermometer, hydrocarbon radical, and so on.

Thus, to distinguish a simple substance from an element by name, the latter is written with a capital letter.

If we write Carbon, we mean the element that is part of a huge number of organic and inorganic substances like carboxylic acids, carbonates, carbides, carbonyls, but under the term "carbon" we understand a simple substance (graphite, diamond, fullerene, etc.) with a specific crystalline lattice structure.

Complex substances can have a molecular structure (including halogen acids HCl, HF, HI, hydrogen sulfide H₂S, methane CH₄, benzene C₆H₆) and a non-molecular structure (ionic or crystalline).

For example, potassium hydroxide KOH, sodium chloride NaCl, lithium oxide Li₂O are typical ionic compounds, which under normal conditions are solid crystalline substances.

They can exist as molecules only at high temperatures in the gaseous state. All metals except mercury have a crystalline structure.

The subject of study in medicine is living organisms, which are complex systems from the standpoint of biology, chemistry, and physics.

Based on these fundamental natural sciences, new disciplines have emerged - biochemistry, biophysics, bioorganic, and bionorganic chemistry, which use their own methods to study living organisms.

What is living substance and is there a connection between living and nonliving? It is known that the properties of living substance include its chemical composition, internal energy, and the ability to preserve and transmit genetic information.

Living organism is an open thermodynamic system consisting of proteins and other organic and inorganic substances, capable of self-renewal, growth, and metabolism.

All living organisms on planet Earth have a cellular structure and are similar in elemental composition. Academician V. Vernadsky also pointed out the close connection between the chemical composition of the Earth's crust and ocean with the chemical composition of living organisms. He believed that living organisms and the Earth's crust create a unified system.

From a chemical point of view, the unity of living and nonliving lies in their similarity in chemical composition. Substances of living and nonliving nature consist of the same chemical elements and are subject to the same chemical interaction forces.