Early history
The idea that matter is composed of discrete units and can be arbitrarily divided has been circulated for thousands of years, but these ideas are only based on abstract philosophical reasoning, not experimental and empirical observation. With the passage of time, the change of culture and school, the nature of atoms in philosophy has also changed greatly, and this change often has some spiritual factors. Nevertheless, the basic concept of atom is still adopted by chemists after thousands of years, because it can concisely explain some new discoveries in the field of chemistry.
The earliest existing explanation of the concept of atom can be traced back to ancient India in the 6th century BC. Rationalism and triumphalism have developed a complete theory to describe how atoms form more complex objects (first in pairs, then in pairs). Western literature is a century later, which was put forward by Le Xipu, and his student democritus summed up his views. Around 450 BC, democritus coined the word atom, which means it can't be cut. Although Indian and Greek atomic views are only based on philosophical understanding, modern scientific circles still use the name created by democritus [1]. Around the 4th century AD, China philosopher Mo Zhai also independently put forward the concept of finite separability of matter in his book Mo Jing, and called the smallest separable unit "end".
modern history
16 1 year, the natural philosopher robert boyle published The Doubtful Chemist. He believes that matter is composed of different "particles" or atoms, not basic elements such as gas, earth, fire and water [2]. Engels believed that Boyle was the first chemist who established chemistry as a science [25].
1789, the French aristocrat lavoisier defined the word atom. Since then, atoms have been used to represent the smallest unit of chemical change.
The atom described by Dalton in the new system of chemical philosophy is 1803. John dalton, an English teacher and natural philosopher, used the concept of atom to explain why different elements always react in integer multiples, that is, the law of multiple proportion. This also explains why some gases are more soluble in water than others. He proposed that each element contains only one kind of atom, and these atoms combine with each other to form compound [3].
1827, British botanist robert brown observed the dust on the water surface with a microscope and found that they were moving irregularly, which further proved the particle theory. Later, this phenomenon was called Brownian motion.
In 1877, Deschauer proposed that Brownian motion is caused by the thermal motion of water molecules.
1897, in the work of cathode ray, physicist Joseph ·J·J· Thomson discovered electrons and their subatomic characteristics, and shattered the hypothesis that atoms are inseparable. Thomson believes that electrons are evenly distributed throughout the atom, just as they are scattered in a sea of uniform positive charges, and their negative charges cancel out those positive charges. This is also called the raisin pudding model [4].
1909, under the guidance of physicist ernest rutherford, Philip Leonard bombarded gold foil with helium ions. It is found that the deflection angle of a small number of ions is much larger than that predicted by Thomson hypothesis. Rutherford pointed out that most of the mass and positive charges in an atom are concentrated in the nucleus at the center of the atom, while electrons surround the nucleus like planets around the sun. When positively charged helium ions pass near the nucleus, they will be reflected at a large angle [5]. This is the nuclear structure of the nucleus.
19 13 years, in the experiment of radioactive decay products, radiochemist Frederic Soddy found that there are often more than one atom for each position in the periodic table of elements [6]. Margaret Todd coined the term isotope to represent different kinds of atoms in the same element. In the process of studying ionic gas, Thomson invented a new technology, which can be used to separate different isotopes, and finally led to the discovery of stable isotopes [7]; In the same year, physicist niels bohr revisited Rutherford's model and linked it with Planck's and Einstein's quantization thoughts. He believes that electrons should be located in some orbits inside atoms and can jump between different orbits, instead of moving inward or outward freely as previously thought. When electrons jump between these fixed orbits, they must absorb or release certain energy. This electronic transition theory can well explain the line with fixed position in the spectrum of hydrogen atom [8], and relate the Planck constant and Rydberg constant in the spectrum of hydrogen atom.
19 16 german chemist Kossel concluded after investigating a large number of facts that the atoms of any element should make the outermost layer satisfy the 8-electron stable structure [1 1].
19 19 years, physicist Rutherford discovered protons in the experiment of alpha particles bombarding nitrogen atoms [24]. Francis William Aston used mass spectrometry to prove that isotopes have different masses, and the mass difference between isotopes is an integer, which is the so-called integer rule.
1923, American chemist Gilbert Newton g.n. Lewis developed Cosell theory and put forward valence bond electron pair theory [1 1]. Lewis assumes that the electrons of one atom and another atom in the molecule form chemical bonds between atoms in the form of "electron pairs". This was a hypothesis that was contrary to the orthodox theory at that time, because Coulomb's law showed that two electrons were mutually exclusive, but Lewis's hypothesis was quickly accepted by the chemical community, which led to the hypothesis of the opposite spin between atoms [15].
1926, Schrodinger (Irving Schrodinger? Dinger) uses the wave-particle duality hypothesis put forward by louis broglie in 1924 to establish a mathematical model of an atom, and describes electrons as three-dimensional waveforms. But mathematically, the exact values of position and momentum cannot be obtained at the same time.
1926, Werner Heisenberg put forward the famous uncertainty principle. This concept describes that only an uncertain momentum range can be obtained for a certain position to be measured, and vice versa. Although this model is hard to imagine, it can explain some previously observed properties of atoms that cannot be explained, such as the spectral lines of atoms larger than hydrogen. Therefore, people no longer use Bohr's atomic model, but regard the atomic orbit as the region where electrons appear with high probability (electron cloud) [9].
1930, scientists found that when α -rays bombard beryllium -9, they will produce an electrically neutral ray with strong penetrating power. At first, it was considered as a gamma ray. 1932, Mr. and Mrs. Aurio Curie discovered that this ray can generate protons from paraffin; In the same year, james chadwick, a student of Rutherford, determined that it was a neutron [1][24], and an isotope was redefined as an element with the same number of protons but different neutron numbers.
1950s With the development of particle accelerators and particle detectors, scientists can study collisions between high-energy particles. They found that neutrons and protons are a kind of hadrons, and they are made up of smaller quark particles. The standard model of nuclear physics has also been developed, which can successfully explain the interaction between the whole nucleus and subatomic particles at the subatomic level.
1985, Steven Chu and his colleagues developed a new technology in Bell Laboratories, which can cool atoms with lasers. William daniel phillips's team managed to put nano-atoms into magnetic traps. These two technologies, together with a method based on Doppler effect developed by Claude Cohen-Donucci's team, can cool a small amount of atoms to the temperature range of micro Kelvin, so that atoms can be studied with high precision, which lays the foundation for the discovery of Bose-Einstein condensation [10].
Historically, because a single atom is too small, it is considered impossible to conduct scientific research. Recently, scientists have successfully used a single metal atom to connect with organic ligands to form a single electron transistor. In some experiments, atoms are slowed down and captured by laser cooling, which can bring a better understanding of matter.
Development history of theoretical model of atomic structure
Dalton's atomic model
John dalton, a British natural scientist, transformed the speculative atomism of ancient Greece into quantitative chemistry theory and put forward the world's first atomic theory model. His theory mainly has the following three points [1 1]:
(1) All matter is composed of very tiny and inseparable matter particles, namely atoms;
(2) All kinds of properties and masses of atoms of the same element are the same, while atoms of different elements mainly show different masses;
(3) Atoms are tiny, indivisible solid spheres;
(4) The atom is the smallest unit involved in chemical changes. In chemical reactions, atoms are just rearranged and will not be created or disappeared.
Although it was proved to be a failed theoretical model by later generations, Dalton brought atoms from philosophy into chemical research for the first time, which made clear the direction of future chemists' efforts, and chemistry really got rid of ancient alchemy, so Dalton was praised as "the father of modern chemistry" by later generations.
Raisin pudding model
The raisin pudding model proposed by Thomson is the first atomic model with subatomic structure.
On the basis of the discovery of electrons, Thomson put forward the atomic raisin pudding model, and Thomson thought [1 1]:
① Positive charges are evenly distributed in atoms like fluid, and electrons are dispersed in positive charges like raisins, and their negative charges and those positive charges cancel each other out;
(2) When excited, electrons will leave atoms and produce cathode rays.
Thomson's student Rutherford completed the experiment (scattering experiment) of alpha particles bombarding gold foil, which denied the correctness of the raisin pudding model.
Saturn model
In the same year that Thomson proposed the raisin pudding model, Japanese scientists proposed Saturn model, arguing that electrons are not evenly distributed, but concentrated in a fixed orbit around the nucleus [16].
Planetary model
The planetary model was put forward by Rutherford based on classical electromagnetism, and its main contents are [1 1]:
Most of the volume of (1) atom is empty;
(2) There is a very small and extremely dense nucleus at the center of the atom;
(3) all the positive charges of atoms are in the nucleus, and almost all the mass is concentrated in the nucleus. Electrons with negative charges move around the nucleus at high speed in nuclear space.
With the progress of science, the fact of linear spectrum of hydrogen atom shows that the planetary model is incorrect.
Bohr's atomic model
In order to explain the linear spectrum of hydrogen atom, Bohr, a student of Rutherford, accepted Planck's quantum theory and Einstein's photon concept, and put forward an atomic structure model of layered arrangement of extranuclear electrons on the basis of planetary model. The basic idea of Bohr's atomic structure model is [12]:
(1) The electrons in the atom move around the nucleus in a circular orbit with a certain radius and do not radiate energy.
(2) Electrons with different orbital motions have different energy (E), and the energy is quantized. Orbital energy follows n( 1, 2, 3, ...), and n is called quantum number. Different orbits are named K(n= 1), L(n=2), N(n=3), O(n=4) and P(n=5) respectively.
③ When and only when electrons jump from one orbit to another, they will radiate or absorb energy. If the radiated or absorbed energy is expressed and recorded in the form of light, a spectrum is formed.
Bohr's atomic model explains the linear spectrum of hydrogen atom well, but it can't do anything about more complicated spectral phenomena.
Modern quantum mechanical model
Physicists De Broglie, Schrodinger, Heisenberg, etc., after 13 years of hard argumentation, have well explained many complex spectral phenomena on the basis of Bohr atom model in modern quantum mechanics model, the core of which is wave mechanics. In the Bohr atomic model, the orbit has only one quantum number (principal quantum number), but the modern quantum mechanics model introduces more quantum numbers (quantum numbers) [1 1] [12].
① principal quantum number and principal quantum number decided on different electron layers, named K, L, M, N, O, P and Q.
(2) angular quantum number and angular quantum number decide different energy levels. Symbol "L" * * n values (1, 2, 3, ... n- 1), with symbols of S, P, D and F, indicate that the motion state of electrons is related to L for multi-electron atoms.
③ The magnetic quantum number determines the orbits of different energy levels, and the symbol is "m" (see "magnetic moment" below). Only useful when a magnetic field is applied. The three quantities "N", "L" and "M" determine the motion state of an atom.
(4) Spin m.q.n Electrons in the same orbit have two kinds of spins, namely "↑↓". At present, the nature of spin phenomenon is still under discussion.