Evolution of atomic structure model

The evolution of the atomic structure model is as follows:

The development of atomic structure model refers to the process of discovering and proposing new atomic structure models from the first atomic structure model proposed by Dalton in 1803.

The history of human understanding of atoms can be roughly divided into five stages:

(1) Ancient atomism.

(2) Dalton atomism.

(3) Thomson atomic model and Rutherford atomic model.

(4) Bohr atomic model.

(5) Quantum mechanical model of atomic structure (electron movement outside the nucleus).

Introduction to atoms

Atoms are the smallest units of ordinary substances that constitute chemical elements; Atoms are also the smallest particles in chemical changes and the smallest unit of chemical properties of elements.

Second, the composition of atoms.

Atoms consist of positively charged nuclei and negatively charged electrons. The number of positive charges carried by the nucleus is equal to the number of negative charges carried by electrons outside the nucleus, so atoms are electrically neutral. Atoms can directly form molecules, ions or substances.

When the number of protons is the same as the number of electrons, the atom is electrically neutral, which is called neutral atom; Otherwise, it is a positively or negatively charged ion. According to the number of protons and neutrons, the types of atoms are different: the number of protons determines which element the atom belongs to, while the number of neutrons determines which isotope the atom is.

Properties of atoms:

One. decay

Radioactivity Each element has one or more isotopes with unstable nuclei, which may undergo radioactive decay. In this process, the nucleus can release particles or electromagnetic radiation. When the radius of the nucleus is larger than that of the strong force, radioactive decay may occur, and the radius of the strong force is only a few femtometers.

Second, the magnetic moment

Basic particles have an inherent property, just like an object rotating around the center of mass has angular momentum in macroscopic physics, which is called spin in quantum mechanics. But strictly speaking, these particles are just points and cannot be rotated. The unit of spin is the reduced Planck constant, and the spins of electrons, protons and neutrons are all half.

In atoms, electrons move around the nucleus, so they have orbital angular momentum besides spin. For the nucleus, the orbital angular momentum comes from its own spin.

Third, the energy level.

In an atom, the potential energy of an electron is inversely proportional to its distance from the nucleus. Measure the potential energy of electrons. Usually, the energy required for an electron to leave an atom is measured. The unit is electron volts.

In the quantum mechanical model, electrons can only occupy a group of states centered on the nucleus, and each state corresponds to an energy level. The lowest energy level is called the ground state and the higher energy level is called the excited state.