Question

For each of the questions, four choices have been provided. Select the correct alternative. (1) As long as an electron revolves in a particular orbit, the electron does not lose its energy. Therefore, these orbits are called stationary orbits and the electrons are said to be in station- ary energy states. (2) Each orbit or shell is associated with a definite amount of energy. Hence, these are also called energy levels. (3) An electron jumps from a lower energy level to a higher energy level, by absorbing energy. It jumps from a higher energy level to a lower energy level by emitting energy in the form of electromagnetic radiation. (4) Electrons move around the nucleus in specified circular paths called orbits or shells or energy levels and are designated as \(\mathrm{K}, \mathrm{L}, \mathrm{M}\) and \(\mathrm{N}\) shells respectively. Arrange the above postulates of Bohr's theory in a correct sequence. (a) \(4,1,3,2\) (b) \(4,2,1,3\) (c) \(4,1,2,3\) (d) \(2,4,1,3\)

Short answer

Question: Arrange the following statements related to Bohr's theory in the correct sequence: 1. Electrons do not lose energy when they revolve in stationary orbits. 2. Each orbit is associated with a definite amount of energy. 3. Electrons absorb or emit energy when they jump between energy levels. 4. Electrons move around the nucleus in specified circular paths called orbits or shells. Answer: The correct sequence of statements is 4, 2, 1, 3.

Step-by-step solution

Recall and understand Bohr's postulates

Before solving the exercise, we must recall and understand the postulates of Bohr's theory, which explain the behavior of electrons in atoms. We are given the statements of these postulates in the exercise, but we need to arrange them in the correct sequence.

Determine the correct order of the postulates

Observing the given statements and options, we can see that statement (4) is the first postulate as it states that electrons move around the nucleus in specified circular paths called orbits or shells, and they are designated as K, L, M, and N shells respectively. After establishing the concept of orbits or shells in which electrons revolve, the next postulate of Bohr's theory is that each of these orbits or shells is associated with a definite amount of energy. Hence, statement (2) logically follows statement (4) Now that we have an understanding of energy levels in the orbits, the third postulate discusses the behavior of electrons present in these energy levels. Statement (1) explains that as long as an electron revolves in a particular orbit, the electron does not lose its energy, and hence these orbits are called stationary orbits. Finally, statement (3) explains how electrons transition between energy levels - if an electron jumps from a lower energy level to a higher one, it absorbs energy; and if it jumps from a higher energy level to a lower one, it emits energy in the form of electromagnetic radiation. Therefore, the correct sequence is \(4, 2, 1, 3\).

Identify the correct answer option

The correct answer is the option that corresponds to the sequence of statements we determined in Step 2, which is \(4,2,1,3\). Reviewing the answer options, we can see that option (b) matches this sequence. Answer: (b) \(4,2,1,3\)

Key concepts

Stationary Orbits

According to Niels Bohr's atomic model, electrons move in specific paths around the nucleus without losing energy, as long as they remain in their designated paths, these paths are called stationary orbits.

The concept of these orbits is fundamental since it provides a stable structure to the atom. In contrast to classical physics, which predicted that charged particles like electrons would radiate energy, Bohr's theory suggests that these orbits are an exception and electrons can orbit indefinitely without radiating energy. When an electron is in one of these stationary orbits, it is said to be in a stationary energy state, a key concept in understanding the stability of atoms.

Energy Levels

Bohr’s atomic theory further postulates that each stationary orbit has a fixed energy level associated with it. These energy levels are quantized, meaning that electrons can only exist at certain energy levels, not in-between.

This quantization of energy is why atoms have a discrete set of possible states they can be in, much like rungs on a ladder. Electrons can move between these levels, but they can only occupy the specific energies that the levels allow. This concept explains why atoms absorb or emit light at specific wavelengths, which corresponds to the energy differences between these fixed levels. Understanding these levels is crucial for explaining the atomic spectrum, chemical bonding, and the reactivity of elements.

Electron Transitions

Bohr's model provides an explanation for the phenomenon of electron transitions. An electron can move from one energy level to another, under specific conditions involving the absorption or emission of energy.

An electron that absorbs the right amount of energy can 'jump' to a higher energy level, known as an 'excited state'. Conversely, when an excited electron falls back to a lower energy level, it releases the excess energy. These transitions are the core reason behind the emission of light in different wavelengths, leading to the unique spectra of elements. Such transitions are also pivotal in understanding the chemical and physical properties of the elements, as they play a crucial role in chemical reactions.

Electromagnetic Radiation Emission

A remarkable consequence of electron transitions is the emission of electromagnetic radiation. When an electron drops from a higher energy level to a lower one, it must emit the energy it had absorbed to make the upward transition.

The energy is released in the form of electromagnetic radiation, which can be visible light or other forms of radiation, depending on the energy difference between the levels. This radiation is not arbitrary; it has a specific frequency and wavelength, which corresponds to the energy gap between the initial and final orbits. This aspect of Bohr’s theory helps explain why gases emit light at specific frequencies when heated (spectral lines) and has profound implications for technologies such as lasers and quantum computing.