Bohr’s Atomic Model And Its Postulates

To address the concerns expressed about Rutherford’s atomic model, Neils Bohr proposed some postulates regarding the atomic model. These postulates stated that only specific unique orbits known as discrete orbits of electrons are permitted inside the atom. Also, electrons do not emit energy when rotating in distinct orbits. This model solved the stability problem in the earlier Rutherford model of the atom, which depicted electrons losing energy and spiralling into the nucleus due to the emission of electromagnetic radiation through the charged particles. The classical law of physics and the quantum theory of radiation supported Bohr’s approach.

Bohr’s Atomic Model And Its Postulates

Niels Bohr’s atomic theory includes electrons with set sizes and energies travelling in orbits encircling a positively charged nucleus, comparable to how planets circle the sun. To summarise Bohr’s atomic model, the energy levels of the electrons are concentrated on the size of the orbits. As a result, electrons in narrower orbits will have lesser energy. Atoms are unstable because electrons move to lower orbits, generating radiation. Therefore, an atom on the smallest orbit will be fully stable since the electron would not have a lower orbit to hop to. As a result, it was postulated that an electron could move between these orbits by obtaining or losing photons (energy).

Advancements leading to Bohr’s Model of An Atom

Previously, findings from investigations of radiation interactions with matter had revealed a wealth of knowledge about the structure of atoms and molecules. Niels Bohr used these findings to expand on Rutherford’s model. Two advances were critical in forming Bohr’s model of the atom. These were:

• The dual nature of electromagnetic radiation indicates that radiations have both wave-like and particle-like qualities.

• Experimental observations concerning atomic spectra could only be described by considering quantized electronic energy levels in atoms.

The following are the main aspects of Niels Bohr’s atomic model:

• In an atom, negatively charged electrons orbit a positively charged nucleus. These electrons follow distinct circular routes known as orbits or shells.

• In this atomic model, every one of the circular routes has a set energy level and is referred to as an orbital shell.

• The energy levels of electrons in various orbits are denoted by n= 1, 2, 3, and so on (integers) and are called quantum numbers. Accordingly, these numerals are allocated to shells such as K, L, M, and N, which stand for 1, 2, 3, and 4.

• An electron’s lowest energy level is n=1, which is closest to the nucleus and is commonly referred to as the ground state.

• An electron may move to a greater energy level or orbital shell by receiving energy (or photons). It might move to a lower energy level or orbital shell by losing energy.

Bohr’s Model For Hydrogen Atom

Bohr’s Atomic Model and its Postulates are given below:

• The electron in a hydrogen atom can travel in a spherical route with a set radius and energy circling the nucleus. Orbits, stationary states, and permitted energy states are all names for these routes. These orbits are positioned in concentric circles around the nucleus.

• The energy of an electron in orbit remains constant over time. Yet, when the electron or energy collects, the requisite quantity of energy is released whenever the electron goes from a higher stationary state to a lower stationary state, the electron will travel from a lower stationary state to a higher stationary state. The energy transition does not occur continuously.

• When a transition occurs between two stationary states that differ in energy by ΔE, the frequency of radiation received or emitted is measured as:

ν= ΔE/h = (E2-E1)/h

Here E2 is the energy of the lower state and E1 represents the energy of the higher state. This is usually referred to as Bohr’s frequency rule.

The angular momentum of an electron in a given stationary state may be represented as follows-

meνr= n.(h/2π)

Therefore, an electron may only travel in orbits where its angular momentum is an integral multiple of h/2π; that is why only specific fixed orbits are permitted.

Inferences based on the Bohr’s Model For Hydrogen Atom are

• The stationary states of electrons are denoted by the numbers n = 1,2,3, and so on. Principal quantum numbers are the names given to these integral numbers.

• The radii of the stationary states are denoted by the symbol rn.

So, rn= n2a0

As a result, the radius of the initial stationary state, known as the Bohr orbit, is 52.9pm. The electron in the hydrogen atom is typically found in this orbit (n=1). The value of r will grow as n increases. In simple terms, the electron would exist outside of the nucleus.

• The energy of the electron’s stationary state is the most essential feature linked with it. The phrase En demonstrates this.

En= – RH (1/n2), where RH stands for Rydberg constant.

• Bohr’s theory may also be applicable to ions with only one electron, such as those found in hydrogen atoms. For instance, He+, Li2+, Be3+, etc. The phrase En denotes the energy of the stationary states involved in similar ions (often called hydrogen-like species).

En= -2.18 x 10-18 (Z2/n2)

• We may also calculate the velocities of electrons travelling in these orbits. The magnitude of electron velocity rises qualitatively with increasing positive charge on the nucleus and decreases with an increasing main quantum number.

Conclusion

Bohr’s atomic model suggests how electrons in atoms move in circular orbits surrounding a central nucleus and can therefore circle securely at a specific collection of lengths from the nucleus in particular predetermined circular orbits. These orbits are associated with specific energies and are also known as energy shells or energy levels. Bohr’s atomic model was the forerunner of quantum mechanical models. This atomic model theory is primarily valid for Hydrogen like elements (single electron systems), such as Lithium+2. However, it helps comprehend other scientists’ postulated atomic models.