The Evolution of the Atomic Model: From the Old Solar System Model to Electron Orbitals

Discover the differences between the old solar system model and the modern understanding of electron orbitals. Learn how this shift impacts our comprehension of electric current, conductors, and insulators. Gain insights into the implications of electron behavior within atoms and its relevance to advancements in materials science and electrical engineering.

The study of atoms, the fundamental building blocks of matter, has undergone significant advancements over the past century. One crucial aspect of this progress lies in the understanding of electron behavior within atoms. In the early days, the old solar system model portrayed electrons as orbiting around the nucleus in fixed circular paths. Resembling planets orbiting the Sun. However, the new understanding of electron orbitals has revolutionized our perception of atomic structure. In this article, we will explore the differences between the old and new models of the atom. Focusing on electron orbitals and how they relate to electric current, conductors, and insulators.

Old solar system model
Solar System Model-

The Old Bohr Model

In the old solar system model, proposed by scientists like Niels Bohr, electrons were depicted as revolving around the nucleus in distinct circular orbits at fixed distances. Each orbit represented a specific energy level. Electrons were thought to remain in their respective orbits without any transition between them. This model was useful in explaining some experimental observations, such as the discrete emission spectra of elements. However, it fell short when attempting to explain more complex phenomena. Such as the behavior of atoms with more than one electron.

The New Quantum Model

The new understanding of electron behavior stems from quantum mechanics. A branch of physics that emerged in the early 20th century. According to the modern view, electrons do not follow well-defined paths like planets orbiting the Sun. Instead, they exist in regions around the nucleus known as electron orbitals or electron clouds. These electron orbitals represent the probability of finding an electron at a particular location within an atom.

electron orbitals of the atomic model
Spatial arrangement of orbitals in the carbon atom in the case of (a) sp, (b) sp 2 and (c) sp 3 hybridizations.-

Electrons in Orbitals

Electron orbitals are characterized by their shapes, sizes, and energies. They are represented by mathematical functions called wavefunctions, which describe the spatial distribution of electrons. The three most commonly known types of orbitals are s, p, and d orbitals, each with a distinct shape. The s orbital is spherical, while p orbitals take on the shape of dumbbells aligned along different axes. The d orbitals are more complex in shape, resembling cloverleaf patterns.

The concept of electron orbitals revolutionizes our understanding of atomic structure. Providing a more accurate depiction of electron behavior and their distribution in space. Rather than assuming fixed paths, electrons exist in a superposition of all possible orbitals, displaying both wave-like and particle-like properties. This wave-particle duality allows electrons to occupy multiple orbitals simultaneously, leading to phenomena such as electron interference and diffraction.

electron orbitals of the atomic model
S,P,D,F Orbitals-

Conductivity in the Quantum Model

Now, let’s explore how this new understanding of electron orbitals relates to electric currents, conductors, and insulators. In the context of electric current, the movement of electrons is crucial. In conductive materials, such as metals, the outermost electrons of atoms are loosely bound and are referred to as “free electrons.” These free electrons can move within the material under the influence of an electric field. Which creates a flow of charge known as electric current.

In terms of electron orbitals, electric current can be understood as the movement of these free electrons between orbitals. When a voltage is applied across a conductor, it creates an electric field that exerts a force on the free electrons, causing them to move. However, it’s important to note that individual electrons do not flow in a straight line from one end of the conductor to the other. Instead, they experience collisions with other electrons and lattice ions, leading to a random motion called electron drift.

In Band Theory, it is said that certain conductive materials have what’s called a conduction band, which exists just above the valence layer of an atom. Electrons travel within this band, through a conductor when current is flowing. In metal conductors, this band actually overlaps the valence layer. This is because the atoms are so much closer together, and form a lattice which gives them their shape.

The conduction band is a band of energy levels that is unoccupied at absolute zero temperature. Electrons can move from the valence band to the conduction band by absorbing energy, such as from a photon of light or from thermal energy. In metals, the conduction band and valence band overlap which means that electrons can easily move from the valence band to the conduction band. This is why metals are good conductors of electric current. So while all electrons exist within orbitals, some orbitals overlap, and electrons move between various energy levels. However, only the electrons in the outermost valence layer move to the conduction band.

Insulators in the Quantum Model

Insulators, on the other hand, have tightly bound electrons that are not free to move within the material. These electrons are confined to their respective orbitals and are not easily influenced by external electric fields. As a result, insulators have very low conductivity and do not allow the flow of electric current.

The behavior of conductors and insulators can be explained in terms of electron orbitals and energy levels. In conductive materials, the presence of overlapping or partially filled orbitals allows electrons to move more freely, facilitating the flow of electric current. In contrast, insulators have completely filled or large energy gaps between their electron orbitals, which makes it difficult for electrons to move and contribute to electric current.

Another way this can be understood is through Band Theory. Insulators have a completely filled valence layer, and a large energy gap stands between the valence and conduction bands. This means that electrons cannot easily move from the valence band to the conduction band, at normal temperatures. This is why insulators are poor conductors of electricity. Within this theory exists a level called the Fermi Layer, which typically sits midway between the valence layer and the conduction band between atoms. Raising and lowering temperatures can increase or decrease electron energy in an atom which allows electrons to become move further from their standard energy level.

At the Fermi level, we most likely find electrons. In conductors, the Fermi level lies within the conduction band. This means that there are always some electrons in the conduction band, even at absolute zero temperature. In insulators, the Fermi level lies within the valence band. This means that there are no electrons in the conduction band at absolute zero temperature.


The new understanding of electron orbitals and their role in electric current provides a more comprehensive and accurate explanation of the behavior of conductors and insulators. By recognizing that electric current involves the movement of free electrons between orbitals, we can better analyze and predict the electrical properties of different materials.

In summary, the shift from the old solar system model to the new understanding of electron orbitals has revolutionized our perception of atomic structure. Electron orbitals represent the probability distribution of electrons around the nucleus and provide a more accurate description of electron behavior within atoms. In terms of electric current, conductors allow the movement of free electrons between orbitals, while insulators restrict electron movement due to their tightly bound electrons. By embracing the new model, we gain a deeper understanding of the behavior of electrons and their involvement in electrical conductivity, leading to advancements in fields such as materials science and electrical engineering. Next up in this series is “Electrical Charges: Positives, Negatives, and Neutrals.

Enjoy learning about electricity?