Atomic Models: After discovering electrons and protons, the scientists started thinking of arranging these particles in an atom. Different models were proposed to explain the distribution of subatomic particles in an atom.
There has been a variety of atomic models throughout the history of atomic physics that refers mainly to a period from the beginning of the 19th century to the first half of the 20th century when a final model of the atom which is being used nowadays (or accepted as the most accurate one) was invented.
Although the awareness of atom existence goes way back to the antique period of world history (Greek conception of an atom).
This article will be mainly about five basic atomic models, from which each one has somehow contributed to how we percept the structure of the atom itself – Dalton’s Billiard Ball Model, J.J Thomson’s “plum pudding” model, Rutherford’s Planetary model, Bohr’s Atomic model, Electron Cloud Model/Quantum Mechanics Model.
Different Types of Atomic Models
1. John Dalton’s Atomic Model
John Dalton was an English scientist who came up with the idea that all matter is composed of tiny things. It was the first complete attempt to describe all matter in terms of particles. He called these particles atoms and formed an atomic theory. In this theory, he claims that:
- All matter is made of atoms. Atoms are indivisible and indestructible.
- All atoms of a given element are identical in mass and properties.
- Compounds are formed by a combination of two or more different kinds of atoms.
- A chemical reaction is a rearrangement of atoms.
Parts of his theory had to be modified based on the discovery of subatomic particles and isotopes. We know that atoms are not indivisible because they are made up of neutrons, electrons, and protons.
2. Plum Pudding Model
After discovering an electron in 1897, people realized that atoms are made up of even smaller particles, shortly after in 1904 J. J. Thomson proposed his famous “plum pudding model. ”
In this model, atoms were known to consist of negatively charged electrons. However, the atomic nucleus had not been discovered yet. Thomson knew that the atom had an overall neutral charge. He thought that there must be something to counterbalance the negative charge of an electron.
He came up with the idea that negative particles are floating within a soup of diffuse positive charges. His model is often called the plum pudding model because of his similarity to a popular English dessert.
Read Full Article On J.J. thomson Atomic Model: J.J Thomson Atomic Model
3. Rutherford’s Atomic Model
Rutherford was first, who suggested that Thomson’s plum pudding model was incorrect. His new model introduces the nucleus to the atom theory. The nucleus contains a relatively high central charge concentrated into a very small volume. This small volume also contains the bulk of the atomic mass of the atom.
Lighter and negatively charged electrons surround the nucleus. His model is sometimes known as the planetary model of the atom. However, there were still some major problems with this model.
For example, Rutherford could not explain why atoms only emit light at certain frequencies. This problem was solved later by Danish physicist Niels Henrik David Bohr.
4. Bohr’s Atomic Model
Bohr model describes the atom as a positively charged nucleus, which is surrounded by electrons. Electrons travel in circular orbits, and electrostatic forces provide attraction. Because the normally occupied energy level of the electron is called the ground state.
The electron can move to the less–stable level by absorbing energy. This higher–energy level is called the excited state. The electron can return to its original level by releasing the energy. All in all, when an electron jumps between orbits, it is accompanied by an emitted or absorbed amount of energy (hv).
5. Electron Cloud Model/Quantum Mechanics Model of Atom
The Quantum Mechanics Model of Atom is nowadays being taught as the most “realistic” atomic model that describes atomic mechanisms and how to present science presumes they work. It came to exist as a result of a combination of the number of scientific assumptions:
- All particles could be perceived as matter waves with a wavelength. (Louis de Broglie)
- Resulting from the previous assumption, the atomic model, which treats electrons also as matter waves were proposed. (Erwin Schrödinger, the quantum mechanical atomic model, emerged from the solution of Schrödinger’s equation for an electron in the central electrical field of the nucleus.)
- Principle of uncertainty states that we can’t know both the energy and position of an electron. Therefore, as we learn more about the electron’s position, we know less about its energy and vice versa. (Werner Heisenberg)
- There exists more than one energy level of the electron in the atom. Electrons are assigned certain atomic orbitals that can differ from one another in energy. (Niels Bohr)
- Electrons have an intrinsic property called spin, and an electron can have one of two possible spin values: spin-up or spin-down. However, any two electrons occupying the same orbital must have opposite spins. (the Stern-Gerlach Experiment)
Here are two models of atomic structure in use today; The Bohr model and the quantum mechanical model. Of these two models, the Bohr model is simpler and relatively easy to understand.
Importance of Atomic Models
As per Dalton’s atomic theory, the atom is the ultimate particle that makes up all matter, and it is indivisible. The discovery of subatomic particles (such as protons, neutrons, and electrons) disproved this assumption.
This led to the requirement for an atomic model that could account for and explain the stability of all atoms and molecules and could also provide a comparison between the differences in the physical and chemical properties of different elements.
Also, atomic models were quite important in explaining the formation of compounds from two or more atoms. It is important to note that atomic models were also required to explain the emission of electromagnetic radiation by atoms, the origin/source of the radiation, and the characteristics of the electromagnetic radiation.