Atoms Flashcards
What experiments in the nineteenth century supported the atomic hypothesis of matter?
Experiments on electric discharge through gases conducted by J. J. Thomson in 1897 revealed negatively charged constituents (electrons) in atoms.
What was J. J. Thomson’s proposed model of the atom, and when was it proposed?
Thomson’s plum pudding model, proposed in 1898, suggested that atoms contain positively charged material with electrons embedded throughout like seeds in a watermelon.
How did the spectrum of light emitted by rarefied gases differ from that emitted by condensed matter or dense gases?
Light emitted by rarefied gases exhibited discrete wavelengths, appearing as a series of bright lines, whereas condensed matter emitted electromagnetic radiation with a continuous distribution of several wavelengths.
What relationship was established between the internal structure of an atom and the spectrum of radiation emitted by it?
Each element was associated with a characteristic spectrum of radiation, implying an intimate relationship between an atom’s internal structure and its emitted spectrum.
Describe Ernst Rutherford’s contribution to atomic structure theory.
Rutherford proposed the planetary model of the atom, also known as the nuclear model, in 1911. He suggested that atoms consist of a dense nucleus containing the entire positive charge and most of the mass, with electrons orbiting around it.
What experiment led to the development of Rutherford’s planetary model of the atom?
The scattering of alpha particles by atoms, proposed by Rutherford in 1906 and later performed by Hans Geiger and Ernst Marsden around 1911, led to the development of Rutherford’s model.
Who was Ernst Rutherford?
Ernst Rutherford was a New Zealand-born British physicist known for his pioneering work on radioactive radiation.
What did Ernst Rutherford discover about radioactive radiation?
Rutherford discovered alpha-rays and beta-rays, contributing significantly to the understanding of radioactive decay.
Who did Ernst Rutherford collaborate with, and what was their contribution?
Rutherford collaborated with Frederick Soddy to create the modern theory of radioactivity, a significant advancement in the field.
What did Rutherford study regarding thorium, and what did he discover?
Rutherford studied the ‘emanation’ of thorium and discovered a new noble gas, an isotope of radon, now known as thoron.
What important discovery did Rutherford make regarding the atomic nucleus?
By scattering alpha-rays from metal foils, Rutherford discovered the atomic nucleus, which led to the proposal of the planetary model of the atom.
What estimation did Rutherford provide in his studies?
Rutherford estimated the approximate size of the nucleus, a significant contribution to the understanding of atomic structure.
What experiment did H. Geiger and E. Marsden perform in 1911, as suggested by Ernst Rutherford?
H. Geiger and E. Marsden directed a beam of 5.5 MeV alpha particles emitted from a 214Bi radioactive source at a thin metal foil made of gold.
Describe the setup of the experiment conducted by H. Geiger and E. Marsden.
The alpha particles emitted by the radioactive source were collimated into a narrow beam by passing through lead bricks. This beam was directed at a thin foil of gold with a thickness of 2.1 × 10^–7 m. The scattered alpha particles were observed through a rotatable detector consisting of a zinc sulfide screen and a microscope.
How were the scattered alpha particles observed in the experiment?
The scattered alpha particles, upon striking the screen, produced brief light flashes or scintillations, which were observed through a microscope.
What did the distribution of the number of scattered particles allow researchers to study?
The distribution of the number of scattered particles allowed researchers to study the scattering angle as a function of the angle of scattering.
What was the significance of the agreement between experimental data and theoretical prediction in Rutherford’s experiment?
The agreement between experimental data and theoretical prediction supported the hypothesis of the nuclear atom, leading to Rutherford’s discovery of the nucleus.
Describe Rutherford’s nuclear model of the atom.
In Rutherford’s nuclear model, the entire positive charge and most of the mass of the atom are concentrated in a small, dense nucleus, while electrons orbit around the nucleus at a distance.
What did Rutherford’s experiments suggest about the size of the nucleus compared to the size of the atom?
Rutherford’s experiments suggested that the nucleus is about 10^–15 m to 10^–14 m in size, whereas the size of an atom is about 10^–10 m, making the nucleus significantly smaller.
What was the assumption made about the scattering of alpha particles in the gold foil?
It was assumed that alpha particles would suffer not more than one scattering during their passage through the thin gold foil.
What forces were involved in computing the trajectory of an alpha particle in Rutherford’s experiment?
The trajectory of an alpha particle was computed using Newton’s second law of motion and Coulomb’s law for the electrostatic force of repulsion between the alpha particle and the positively charged nucleus.
How does the impact parameter affect the trajectory of an alpha particle?
The trajectory of an alpha particle depends on the impact parameter, which is the perpendicular distance of the initial velocity vector of the alpha particle from the center of the nucleus. A smaller impact parameter results in a larger scattering angle, while a larger impact parameter leads to a smaller deflection.
