Question

The current model of the atom in which essentially all of an atom's mass is contained in a very small nucleus, whereas most of an atom's volume is due to the space in which the atom's electrons move, was established by a. Millikan's oil-drop experiment. b. Thomson's cathode-ray-tube experiment. c. Dalton's atomic theory. d. Rutherford's metal foil experiment. e. Bohr's hydrogen model.

Short answer

The correct experiment that established the current atomic model with a small nucleus containing most of an atom's mass and electrons occupying most of an atom's volume is Rutherford's metal foil experiment (option d).

Step-by-step solution

Review Millikan's Oil-Drop Experiment

Millikan's oil-drop experiment measured the charge of an electron. Though it was a significant experiment, it didn't reveal information regarding the distribution of mass and volume in an atom.

Review Thomson's Cathode-ray Tube Experiment

Thomson's cathode-ray tube experiment led to the discovery of the electron and the proposal of the plum pudding model of the atom. This model does not match the description given in the question.

Review Dalton's Atomic Theory

Dalton's atomic theory provided the foundation for our understanding of atoms and their behavior. However, it did not provide information about the structure of the atom, particularly regarding the mass and volume distribution.

Review Rutherford's Metal Foil Experiment

Rutherford's metal foil experiment demonstrated that almost all of an atom's mass is concentrated in a small nucleus, while the electrons occupy the vast majority of the atom's volume. This matches the description given in the question.

Review Bohr's Hydrogen Model

Bohr's hydrogen model helped explain the atomic structure by introducing the quantization of energy levels for electrons orbiting the nucleus. However, it doesn't specifically address the distribution of mass and volume within an atom.

Choose the correct experiment

Based on our analysis, Rutherford's metal foil experiment (option d) is the correct answer, as it established that almost all of an atom's mass is contained in a small nucleus, while the electrons occupy the majority of the atom's volume.

Key concepts

Rutherford's Metal Foil Experiment

The Rutherford metal foil experiment marks a pivotal moment in the understanding of atomic structure. In attempting to probe the interior of the atom, Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden directed alpha particles at a thin sheet of gold foil. The prevailing model at the time was J.J. Thomson's 'plum pudding model', which implied a uniform distribution of mass and charge within the atom.

What Rutherford observed was revolutionary: while most alpha particles passed straight through the foil, a small fraction were deflected at large angles, and some even rebounded directly back toward the source. This suggested that the atom was mostly empty space, containing a central nucleus that was both dense and positively charged. Thus, the bulk of an atom's mass was concentrated in this central nucleus, overturning Thomson's model and leading to the Rutherford atomic model – a tiny, dense nucleus surrounded by orbiting electrons.

When constructing a model of atomic structure, Rutherford's experiment highlights the importance of the nucleus as a tiny, dense center of mass, around which electrons reside in vast empty space. It shifted the scientific perspective from an atom being a 'pudding' of distributed charge to one having a defined and centralized core.

Atomic Model

The atomic model has evolved over time as scientists have gathered new evidence and insights into the nature of matter. Initially, the atom was considered indivisible and solid, as per Dalton's atomic theory in the early 19th century. This changed with the discovery of electrons by J.J. Thomson, leading to his 'plum pudding' model suggesting a diffuse cloud of positive charge with embedded electrons.

Rutherford's finding significantly challenged this view and required a new atomic model. Post Rutherford, the understanding deepened with Bohr's model, where electrons were thought to orbit the nucleus in fixed paths or shells. This concept was later refined by quantum mechanical models, which describe electron distribution as a 'probability cloud,' recognizing that electrons are not fixed in precise orbits but are found in varying probabilities at different levels of energy and distances from the nucleus.

In modern education, it is paramount to present the atomic models in a historical context, as they represent our increasing understanding of atomic structure. It teaches us not just about the atom itself, but about the scientific method and how theories evolve with new evidence.

Electron Distribution

Electron distribution in an atom is concerned with how electrons are arranged around the nucleus. Pierre-Simon Laplace and others initially conceived electron distribution akin to planets orbiting the sun. However, with advances in quantum theory, Erwin Schrödinger introduced the quantum mechanical model, which uses complex mathematical functions to predict the likelihood of an electron’s position and energy level.

In this quantum mechanical view, electrons exist in atomic orbitals, which are specific regions of space where electrons are most likely to be found. These orbitals are grouped into energy levels that encircle the nucleus. Understanding electron distribution is crucial for explaining chemical bonding and the properties of elements. Each electron in an atom occupies the lowest energy orbital available, known as the 'Aufbau principle' - an essential concept for chemical reactivity and predicting the behavior of atoms during reactions.

The concepts of electron shells and subshells, as well as orbitals, aid in comprehending the complex arrangements and the periodic table itself. A robust grasp of electron distribution is vital for students as it lays the groundwork for more advanced topics in chemistry such as molecular geometry, reaction mechanisms, and spectroscopy.