History of creation and fundamental law
Modern chemical science is based on the periodic law, which determines the rules and patterns of changes in the characteristics of chemical elements. The visual and systematic expression of this rule is the Periodic Table of Elements, which was first developed and presented to the scientific community by D.I. Mendeleev in 1869.
This table does not simply list existing substances, but strictly organizes them, clearly illustrating how the properties of chemical elements periodically repeat and change. It was this discovery that made it possible to structure all the knowledge accumulated by that time.
Chronological filling and new elements
The Periodic Table is not a static object; it expanded as science developed. A special milestone in the filling of the table is uranium. All chemical elements following uranium in the table were introduced into it strictly in chronological order — as scientists synthesized and discovered them.
The process of updating the system continues in modern times. For instance, the reliable discovery of the two most recent chemical elements was officially and securely confirmed in 2012.
Element cell structure
For ease of use and quick access to information, the Periodic Table is divided into blocks — cells. Each such cell contains a standardized set of brief yet comprehensive information about a specific chemical element.
Let us examine the structure of a typical cell using aluminum as an example:
- Atomic number: 13 (determines position in the table).
- Symbol: Al (international letter designation).
- Name: aluminum (full name).
- Atomic mass: 26.981 (precise quantitative indicator).
Briefly: answers to topical questions
What is the modern formulation of the periodic law?
The modern formulation of the periodic law states that the properties of chemical elements and the substances they form are in periodic dependence on the charges of atomic nuclei.
What is the physical meaning of the atomic number of a chemical element?
The physical meaning of the atomic number of a chemical element is that it is numerically equal to the charge of the atomic nucleus.
Since an atom is an electroneutral particle, the nuclear charge determines both the number of protons inside it and the total number of electrons surrounding the nucleus. Thus, knowing the element's atomic number in the table, one can precisely determine the number of its electrons and protons.
How does the electronegativity of chemical elements change across periods from left to right?
In periods from left to right, the electronegativity of chemical elements increases.
This pattern is confirmed by the electronegativity values for the elements of periods II and III. The lowest values are observed in alkali metals at the beginning of the period, and the highest in halogens at the end.
| Element | Electronegativity |
|---|---|
| Lithium (Li) | 1,0 |
| Fluorine (F) | 4,0 |
| Sodium (Na) | 0,9 |
| Chlorine (Cl) | 3,0 |
Which elements of the Periodic Table belong to s-elements?
S-elements include the chemical elements of groups IA and IIA of the Periodic Table. In the atoms of these elements, the outer s-sublevel is being filled.
Which chemical elements of the Periodic Table are the main organogens?
The main organogen chemical elements include those that account for 98% of the composition of living organisms.
- Carbon (C) — makes up 45–55% of the dry matter of bacteria.
- Oxygen (O) — makes up 25–30%.
- Nitrogen (N) — a structural component of proteins, nucleotides, and coenzymes (8–15%).
- Hydrogen (H) — makes up 6–8%.
Important organogens also include sulfur (S), which is part of proteins, and phosphorus (P), necessary for the synthesis of nucleic acids and ATP.
How do atomic radii of elements in main subgroups change from top to bottom?
In the given example for alkali metals, atomic radii increase from top to bottom: Li — 159 pm, Na — 171 pm, K — 216 pm, Rb — 229 pm, Cs — 282 pm. As the radius increases, the bond between the outer electrons and the nucleus weakens.
Which d-elements of the Periodic Table belong to essential trace elements (biometals)?
Essential d-elements include metals that are part of many enzyme proteins.
List of essential trace elements:
- Manganese (Mn) — essential element.
- Iron (Fe) — essential element.
- Cobalt (Co) — essential element.
- Copper (Cu) — essential element.
- Zinc (Zn) — essential element.
- Molybdenum (Mo) — essential element.
Probable essential biometals also include vanadium (V), chromium (Cr), and nickel (Ni).
Class and exam questions
What is the essence of the Periodic Table?
It combines all known chemical elements and visually expresses the periodic law — the law of periodic variation of the properties of these elements.
When and by whom was this table created?
The system was first compiled by the Russian scientist D.I. Mendeleev in 1869.
How were elements beyond uranium added?
All elements following uranium were added to the table chronologically, strictly as they were actually discovered.
What information is contained in a table cell?
Each cell provides basic information: atomic number, chemical symbol, full name, and atomic mass value.
What else to study on this topic
- Formulation and physical meaning of the periodic law
- Properties of elements located after uranium
- Principles of atomic mass calculation
- The process of verification and confirmation of the discovery of new elements
- The relationship between atomic number and chemical characteristics
Master the entire topic in the "Chemistry" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic "Periodic Table of Chemical Elements" and 3,009 more pages of the subject
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Other topics in the section "Chapter 1. Substances. Properties and Structure"
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