Structure of the Atom

A set of vocabulary flashcards covering sub-atomic particles, atomic models, electron shell distributions, and isotopic definitions from Chapter 4 Structure of the Atom.

Canal Rays

Positively charged radiations discovered by E. Goldstein in 1886 in a gas discharge, which ultimately led to the discovery of the proton.

Electron

A negatively charged sub-atomic particle identified by J.J. Thomson, represented as $e^-$, with a charge of $-1$ and a negligible mass of approximately $\frac{1}{2000}$ times that of a proton.

Proton

A positively charged sub-atomic particle discovered following the observation of canal rays, represented as $p^+$, with a charge of $+1$ and a mass of $1\,u$.

Neutron

A sub-atomic particle discovered by J. Chadwick in 1932 that has no charge and a mass nearly equal to that of a proton, represented as $n$.

Thomson's Model of an Atom

An atomic model proposing that an atom consists of a positively charged sphere with electrons embedded in it, similar to currants in a Christmas pudding or seeds in a watermelon.

Alpha ($\alpha$)-particles

Doubly-charged helium ions with a mass of $4\,u$ and a considerable amount of energy, used in Rutherford's scattering experiment.

Nucleus

The tiny, positively charged centre of an atom containing nearly all its mass, discovered by Ernest Rutherford, with a radius about $10^5$ times smaller than the radius of the atom.

Rutherford's Model of an Atom

A nuclear model of an atom proposing that an atom has a positively charged centre called a nucleus and electrons that revolve around it in circular paths.

Bohr's Model of the Atom

An atomic model proposed by Neils Bohr stating that electrons revolve only in certain special discrete orbits without radiating energy.

Energy Levels

Discrete orbits or shells inside an atom represented by the letters K, L, M, N, … or numbers $n = 1, 2, 3, 4, \dots$ in which electrons revolve.

Bohr-Bury Scheme

A set of rules for electron distribution stating that the maximum number of electrons in a shell is $2n^2$, the outermost orbit can hold at most 8 electrons, and inner shells are filled stepwise.

Valence Electrons

The electrons present in the outermost shell of an atom.

Octet

An outermost electron shell containing eight electrons, representing a stable electron configuration.

Valency

The combining capacity of an atom of an element, determined by the number of electrons gained, lost, or shared to achieve an octet in its outermost shell.

Atomic Number ($Z$)

The total number of protons present in the nucleus of an atom, denoted by $Z$.

Mass Number ($A$)

The sum of the total number of protons and neutrons present in the nucleus of an atom, denoted by $A$.

Nucleons

The protons and neutrons present together inside the nucleus of an atom.

Isotopes

Atoms of the same element having the same atomic number but different mass numbers, such as protium ($^1_1\text{H}$), deuterium ($^2_1\text{H}$), and tritium ($^3_1\text{H}$).

Isobars

Atoms of different elements with different atomic numbers that have the same mass number, such as calcium ($Z = 20$) and argon ($Z = 18$), which both have a mass number of 40.

Applications of Isotopes

Specific practical uses of isotopes, including an isotope of uranium used as fuel in nuclear reactors, an isotope of cobalt used in cancer treatment, and an isotope of iodine used in goitre treatment.