Electron shells of atoms

Evolution of atomic structure concepts

The understanding of how electron shells are organized began with historical experiments by E. Rutherford. Studying the passage of alpha rays through a thin metal foil, researchers concluded that a dense central nucleus exists.

Based on these data, the planetary model of the atom was proposed. In it, the structure of the microworld was likened to the Solar System, where the massive atomic nucleus plays the role of the Sun, and electrons orbiting around it act as the planets. However, subsequent development of science required an important refinement: the real laws of electron motion in the shell differ cardinally from the laws of celestial mechanics governing planetary motion.

Interaction of electrons with energy

A crucial property of atomic structures is their ability to absorb and emit light energy. This phenomenon forms the basis of spectral analysis.

If a light beam is passed through a gaseous substance and then dispersed into a spectrum, characteristic sets of spectral lines can be observed. These lines are strictly individual and reflect the energy transitions of electrons inside the shells of atoms of a specific element.

Wave properties of matter

To describe the behavior of electrons and other microparticles, the de Broglie equation is used. It mathematically proves that any moving object possesses wave properties.

The main formula is: λ = h / (m · v)

Where the parameters are distributed as follows:

• λ — wavelength;
• h — Planck's constant;
• m — mass of the object;
• v — velocity of particle motion.

Nuclear transformations and beta decay

The fundamental difference between nuclear and chemical processes is that during chemical reactions, atoms retain their integrity, whereas during nuclear processes, they undergo decay and transformations. A striking example is the radioactive beta decay of nuclides, accompanied by high-energy radiation.

Let us examine the transformation mechanism of the carbon-14 isotope ($^{14}C$):

1. Initial state: the $^{14}_{6}C$ atom is present in the biosphere in negligible amounts.
2. Intranuclear process: one of the neutrons in the nucleus transforms into a proton.
3. Radiation: the nucleus ejects a high-energy electron (the so-called $\beta$-particle) at immense speed.
4. Formation of a new element: the nuclear charge increases from +6 to +7. Carbon transforms into a nitrogen ion ($^{14}_{7}N^{+}$), which lacks one electron in its shell.
5. Neutralization: the resulting ion captures an electron from the environment, becoming a fully neutral nitrogen atom.

Practical application and safety

The $^{14}C$ isotope is continuously formed in the upper layers of Earth's atmosphere. This process is triggered when cosmic ray neutrons collide with atmospheric nitrogen nuclei: $^{14}_{7}N + n^{0} = ^{14}_{6}C + p$.

This mechanism has found wide application in archaeology. In organic remains (tissues, wool, leather) buried underground, the $^{14}C$ content steadily decreases over time. By measuring the intensity of the $\beta$-particle flux from the studied sample, specialists can accurately determine its historical age.

At the same time, working with radioactive nuclides requires utmost caution in medical and laboratory practice. High-energy radiation accompanying nuclear transformations poses an extreme hazard to health, necessitating strict control over radiation sources.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Quantum-mechanical model of the atom: orbitals and electron spin.
• Principles of electron shell filling (Klechkowski's rule, Pauli exclusion principle).
• Emission and absorption spectra: the Balmer and Lyman series.
• Medical applications of other radioactive isotopes (iodine-131, technetium-99m).

Other topics in "Chapter 5. Structure of Matter"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.