Problem 53 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

When alpha particles are sent through a thin metal foil, most of them go straight through the foil because : (a) alpha particles are much heavier than electrons (b) alpha particles are positively charged (c) most part of the atom is empty space (d) alpha particle move with high velocity

Step-by-Step Solution

Answer

(c) Most part of the atom is empty space.

Step 1: Understanding the Experiment

In this exercise, we are considering the famous Rutherford gold foil experiment, where alpha particles are directed at a thin sheet of metal foil. Observations showed that most alpha particles passed through without deflection.

Step 2: Analyzing the Possible Answers

The options given are reasons for why alpha particles pass through the metal foil: (a) they are much heavier than electrons, (b) they are positively charged, (c) most part of the atom is empty space, and (d) they move with high velocity.

Step 3: Evaluating the Atomic Structure

In the Rutherford experiment, it was concluded that most of the atom is empty space, and the nucleus, which contains most of the atom's mass, occupies very little of the atom's volume. Hence, many alpha particles pass through without encountering anything.

Step 4: Matching with the Correct Answer

The fact that most alpha particles pass straight through the foil is best explained by the atomic structure being mostly empty space. This space allows the alpha particles to proceed without interference.

Key Concepts

Alpha Particles

Alpha particles are positively charged particles that play a crucial role in understanding atomic structure. They are composed of two protons and two neutrons, making them identical to helium nuclei. Because of their positive charge, they are often used in experiments to explore the characteristics of different materials, like in the Rutherford gold foil experiment.
Through this experiment, scientists were able to observe the interactions between alpha particles and the atoms in the gold foil. These interactions were pivotal in uncovering the nature of atoms.
Here are some key characteristics of alpha particles:

• They are relatively heavy and large compared to electrons.
• They have a doubly positive charge due to the presence of two protons.
• They typically travel at high velocities, but can be deflected by the positive charge of an atomic nucleus.

These properties made alpha particles perfect for probing the atomic structure, leading to groundbreaking discoveries about the nature of atoms.

Atomic Structure

The atomic structure was revolutionized by Rutherford's experiments, leading to the model we are familiar with today. Prior to these findings, atoms were thought to be dense and uniform.
The observations from the gold foil experiment challenged this view by revealing an entirely different picture of atomic structure.

• The core conclusion was that atoms have a tiny, dense nucleus where most of their mass is concentrated.
• This nucleus is positively charged and contains the protons and neutrons, while electrons occupy the space around it.
• The vast majority of an atom's volume is not occupied by mass, leading to the idea of mostly empty space within an atom.

This new model not only matched the observations of alpha particle behavior but also paved the way for future research and understanding of atomic physics.

Empty Space in Atoms

One of the most significant revelations from Rutherford's gold foil experiment was the discovery that atoms are mostly empty space. This idea was revolutionary because it contradicted the earlier "plum pudding model," which assumed that atomic mass was evenly distributed.
The empty space concept became evident when most alpha particles passed through the gold foil without any deflection. If atoms were solid, alpha particles would have encountered more resistance.

• This finding implies that the electron cloud around a nucleus is vast compared to the tiny nucleus itself.
• The space accounts for why materials generally appear solid. Despite this, atoms within them are primarily empty space.
• Understanding this concept helps explain phenomena such as atomic interactions and electrical conductivity.

The idea of empty space in atoms has had far-reaching implications, greatly enhancing our comprehension of both atomic and subatomic principles.