Journey Inside the Atom Vocabulary Flashcards

Comprehensive vocabulary flashcards covering historical atomic theories, key subatomic particles, experimental models, and fundamental principles of atomic structure.

Parmanu

The smallest, indivisible, and infinitely small particles of matter proposed more than $2000$ years ago by Indian philosopher Acharya Kanada in the Vaisesika Sutras.

Atomos

The Greek word meaning "cannot be divided further," proposed by Leucippus and Democritus to describe fundamental indivisible particles of matter.

Dalton's Atomic Theory

The first scientific atomic theory proposed by John Dalton in $1808$, stating that all matter is composed of indivisible particles called atoms that combine in fixed ratios to form compounds.

Cathode Rays

Streams of negatively charged particles emitted from the cathode toward the anode in a glass discharge tube under high voltage and very low gas pressure.

Electron

The first identified subatomic particle, discovered by J. J. Thomson in $1897$, carrying a relative charge of $-1$ ($-1.602 \times 10^{-19}\,\text{C}$).

Plum Pudding Model

J. J. Thomson's atomic model depicting the atom as a sphere of positive charge with negatively charged electrons embedded throughout like seeds in a watermelon.

Gold Foil Experiment

An experiment performed in $1911$ by Geiger and Marsden under Ernest Rutherford, bombarding an extremely thin gold foil with a beam of positively charged $\alpha$-particles.

Alpha Particle ($\alpha$-particle)

A tiny positively charged particle emitted from certain radioactive elements, consisting of a helium nucleus containing $2$ protons and $2$ neutrons.

Scattering

The deflection of particles from their original straight trajectory when passing through matter, as observed with $\alpha$-particles in the gold foil experiment.

Nucleus

The dense, central, positively charged region of an atom discovered by Ernest Rutherford, containing all of the atom's positive charge and nearly all of its mass.

Planetary Model of the Atom

Ernest Rutherford's atomic model proposing that electrons revolve around a dense, positive central nucleus, similar to planets orbiting the Sun.

Proton

A heavy, positively charged subatomic particle located in the nucleus, carrying a relative charge of $+1$ equal and opposite to that of an electron.

Stationary States

Fixed circular paths or orbits ($K, L, M, N\dots$) proposed by Niels Bohr in $1913$ in which revolving electrons maintain constant energy without radiating it.

Neutron

An uncharged (neutral) subatomic particle discovered by James Chadwick in $1932$, located in the atomic nucleus with a mass nearly equal to that of a proton.

Nuclear Force

The strong binding force within the nucleus that binds protons and neutrons together, counteracting electrostatic repulsion between positively charged protons.

Atomic Number ($Z$)

The number of protons present in the nucleus of an atom, which uniquely determines the chemical identity of an element.

Mass Number ($A$)

The total number of protons and neutrons (nucleons) present in the nucleus of an atom, calculated as $A = \text{protons} + \text{neutrons}$.

Nucleons

The collective name given to the subatomic particles (protons and neutrons) residing inside the atomic nucleus.

Electronic Configuration

The distribution and arrangement of electrons among the various energy levels or shells ($K, L, M, N$) of an atom.

Valence Shell

The outermost electron shell of an atom.

Valence Electrons

The electrons located in the outermost (valence) shell of an atom, which determine its chemical reactivity.

Octet Rule

The rule stating that an atom is chemically stable and largely unreactive when its outermost shell contains $8$ electrons (or $2$ electrons in the single shell of hydrogen and helium).

Valency

The combining capacity of an atom, equal to the number of electrons gained, lost, or shared to achieve a stable octet or duplet configuration.

Isotopes

Atoms of the same element that have the same atomic number ($Z$) and number of protons, but different mass numbers ($A$) due to varying numbers of neutrons.

Weighted Average Atomic Mass

The average atomic mass of a natural element calculated by multiplying the mass of each isotope by its percent relative natural abundance and adding the products.

Isobars

Atoms of different elements that possess different atomic numbers ($Z$) but share the same mass number ($A$).

IUPAC

The International Union of Pure and Applied Chemistry; an international organization that approves standard names and chemical symbols for elements.

Bhabha Atomic Research Centre (BARC)

An Indian nuclear facility located in Mumbai, named after Homi Jehangir Bhabha, that conducts advanced neutron-scattering experiments using reactors like Dhruva.