Structure of Atom

Vocabulary flashcards covering the discovery and properties of electrons, protons, neutrons, and early atomic models based on lecture notes.

Cathode Ray Discharge Tube Conditions

The experimental setup used for discovering the electron, requiring a low pressure discharge tube ($50\,\text{cm}$), high voltage of $10,000\,\text{V}$, and a pressure of $10^{-4}\,\text{atm}$.

Cathode Rays Deflection Setup

An experimental apparatus showing cathode rays travelling from the cathode through an anode slot and deflecting towards a positively charged plate in an applied electric field.

Cathode Rays

Streams of negatively charged particles that travel in straight lines away from the cathode, cast shadows of metallic objects, possess kinetic energy (rotating a pinwheel), produce light on a $\text{ZnS}$ screen, produce X-rays on high atomic mass targets, affect photographic plates, and ionize gas.

Independence of Cathode Rays

The property that the nature of cathode rays does not depend on either the material of the cathode or the gas inside the discharge tube.

Charge to Mass Ratio ($e/m$) of Electron

A constant value of $-1.76 \times 10^{11}\,\text{C\,kg}^{-1}$, which remains identical regardless of the gas used in the discharge tube or the material of the electrodes.

Oil Drop Experiment

An experiment performed by Millikan to measure the electrical charge of an electron, determined to be $-1.602 \times 10^{-19}\,\text{C}$.

Mass of Electron

Calculated as $m = \frac{e}{e/m} = 9.1 \times 10^{-28}\,\text{g}$ or $9.1 \times 10^{-31}\,\text{kg}$, which is equivalent to $m_e = \frac{1}{1837} \times M_H$.

Discovery of Proton

Discovered by Goldstein through the observation of canal rays, positive rays, or anode rays in a modified discharge tube.

Anode Rays (Canal Rays)

Positively charged rays formed by the loss of electron(s) from gas atoms that travel in straight lines, possess kinetic energy, produce light flashes on a $\text{ZnS}$ screen, and are deflected by electric and magnetic fields.

Charge to Mass Ratio ($e/m$) of Anode Rays

A value much smaller than that of an electron, which depends on the nature of the gas inside the discharge tube and is largest for hydrogen gas.

Discovery of Neutron

Discovered by Chadwick in 1932 by bombarding beryllium or boron with $\alpha$-particles emitted by an isotope of polonium (Po-21).

Mass of Neutron

The rest mass of a neutron, equal to $1.675 \times 10^{-24}\,\text{g}$, or approximately $1.0087\,\text{amu}$.

Thomson's Plum Pudding Model

An atomic model proposing that positive charge is uniformly spread over a sphere with negative electrons embedded inside it to make the atom electrically neutral as a whole.