Question

Discuss the current view of the correctness of the following statements. (a) The electron in the hydrogen atom is in an orbit that never brings it closer than \(100 \mathrm{pm}\) to the nucleus. (b) Atomic absorption spectra result from transitions of electrons from lower to higher energy levels. (c) A many- electron atom behaves somewhat like a solar system that has a number of planets.

Short answer

(a) Incorrect - Electrons exist in probabilistic orbitals. (b) Correct - Absorption spectra from electrons' energy transitions. (c) Incorrect - Atoms are not like solar systems; quantum mechanics applies.

Step-by-step solution

Analyzing Statement (a)

The statement suggests that the electron orbits the nucleus at a minimum distance of 100 pm. According to current atomic theory, especially the quantum mechanical model, electrons are not confined to fixed orbits but rather exist in probabilistic clouds or orbitals. These orbitals represent regions of space where the electron is likely to be found. The traditional Bohr model, which implies fixed orbits, is outdated. Thus, the statement that the electron never gets closer than 100 pm is not aligned with modern views.

Discussing Statement (b)

This statement suggests that absorption spectra are produced when electrons absorb energy and transition from lower to higher energy levels. According to modern quantum mechanics and spectroscopy, this statement is correct. Atomic absorption spectra indeed result from the absorption of specific wavelengths of light by electrons, causing them to move from lower energy levels to higher ones.

Evaluating Statement (c)

This statement compares a many-electron atom to a solar system with multiple planets. While this analogy might be conceptually useful, it is not accurate scientifically. In reality, many-electron atoms are influenced by quantum mechanics where electron-electron interactions, exchange, and correlation effects play significant roles. The simplistic analogy of planets orbiting a sun doesn't adequately capture the complexities of atomic structures.

Key concepts

Quantum Model of Atom

The quantum mechanical model of the atom revolutionized our understanding of atomic structure. This model views electrons not as particles moving in fixed orbits around the nucleus but as existing within regions known as orbitals.

These orbitals are mathematical functions that describe the probability of finding an electron in a particular region around the nucleus:

• Electrons are described by wavefunctions \(\psi\), which, when squared, provide the probability density \(\psi^2\) of the electron's location.
• This means electrons are more like 'clouds' around the nucleus, rather than hard, point-like particles.
• The Heisenberg Uncertainty Principle further emphasizes that we cannot precisely know both the position and momentum of an electron.

The Bohr model's idea of defined electron orbits is replaced by the idea of probabilistic distributions. Therefore, statements about specific orbit distances, such as the electron being no closer than 100 pm from the nucleus as in the original exercise, do not hold true under this modern framework.

Quantum mechanics provides a more nuanced understanding of the atom by allowing for a description that incorporates the likelihood of an electron's position, reflecting the affiliated distance variations between the electron and nucleus.

Atomic Absorption Spectra

Atomic absorption spectra are an essential concept in understanding how atoms interact with energy. When an atom absorbs energy, typically in the form of light or electromagnetic radiation, its electrons gain energy.

Here's what happens during the absorption process:

• Electrons jump from a lower energy orbital to a higher energy orbital.
• This process requires specific amounts of energy, corresponding to particular wavelengths of light absorbed.
• The electron transitions create a unique spectra signature, used in spectroscopy to identify elements.

Absorption spectra are the inverse of emission spectra. While emission involves the release of energy (light) as electrons fall to lower energy levels, absorption involves the intake of energy.

The concept is crucial for techniques such as atomic absorption spectroscopy, which utilizes absorbed wavelengths to determine the presence and concentration of elements in samples. Hence, the exercise's statement regarding absorption is correctly aligned with contemporary scientific understanding.

Electron Cloud

The electron cloud model is a significant component of modern atomic theory, challenging the older concept of electrons revolving in fixed orbits.

In this model, the cloud represents areas where there’s a high probability of finding an electron. The term 'cloud' effectively conveys the idea of a fuzzy boundary that doesn’t have a precise location, reflecting several key aspects:

• Orbital shapes and sizes give insight into electron positions relative to the nucleus.
• The cloud is densest where the probability of finding an electron is highest.
• The shape and orientation of electron clouds are determined by quantum numbers that arise from solutions to the Schrödinger equation.

Electron clouds account for the complex interactions among electrons, especially in many-electron atoms, where electron-electron repulsions and quantum interactions contribute to the overall shape and behavior.

The comparison of a many-electron atom to a solar system doesn't adequately consider the cloud nature and intricate interactions predicted by quantum mechanics. Instead, it highlights the shifts away from simplistic orbits to a richer understanding of atomic dynamics.