Journey Inside the Atom (Chapter 8) Practice Flashcards

This set of vocabulary flashcards covers the historical development of atomic models, subatomic particles, electron distribution, and atomic properties like mass number, valency, isotopes, and isobars.

Matter

Everything that you see, observe, or feel around you, consisting of tiny particles called atoms.

Parmanus

The smallest particles of matter that can no longer be divided, as suggested by Acharya Kanada in the Sanskrit text Vaisesika Sutras.

Atomos

A Greek term meaning indivisible, proposed by philosophers Leucippus and Democritus to describe fundamental particles.

John Dalton's Atomic Theory

Proposed in 1808, it stated all matter is composed of indivisible particles called atoms, which are the fundamental building blocks of matter.

Cathode Rays

Streams of negatively charged particles observed by J. J. Thomson moving from the negative electrode (cathode) to the positive electrode (anode) in a vacuum tube.

Electrons

Fundamental subatomic particles discovered by J. J. Thomson; they carry a charge of $-1.602 \times 10^{-19}\,C$, conventionally taken as $-1$.

Plum Pudding Model

J. J. Thomson's model of an atom as a sphere of positive charge with electrons distributed throughout it, similar to seeds in a watermelon.

Alpha (\alpha) Particles

Tiny, positively charged particles emitted from certain radioactive elements, consisting of a helium nucleus with $2$ protons and $2$ neutrons.

Scattering

The deflection of alpha particles from a straight path when hitting a thin gold foil, discovered in Geiger and Marsden's experiment.

Nucleus

The dense, extremely small central region of an atom that contains all the positive charge and most of the mass.

Planetary Model

Ernest Rutherford's model where electrons revolve around the nucleus similar to planets orbiting the Sun.

Proton

A subatomic particle discovered and named by Rutherford that carries a positive charge equal and opposite to that of an electron and is much heavier.

Bohr's Model of the Atom

A model proposed in 1913 suggesting electrons follow fixed circular paths called stationary states or orbits where they do not lose energy.

Energy Levels

The shells (K, L, M, N or $n = 1, 2, 3, 4$) where electrons revolve; energy increases as the shells move farther from the nucleus.

Neutron

A neutral subatomic particle discovered by James Chadwick in 1932, located in the nucleus with a mass nearly equal to a proton.

Nuclear Force

The force that binds protons and neutrons together in the nucleus, overcoming the repulsion between positive protons.

IUPAC

The International Union of Pure and Applied Chemistry, the organisation that approves the names and symbols of elements.

Atomic Number (Z)

The total number of protons in the nucleus of an atom, which determines the identity and chemical behaviour of an element.

Mass Number (A)

The total number of protons and neutrons (collectively known as nucleons) present in the nucleus of an atom.

Notation of an Atom

The standard representation written as \prescript{A}{Z}{\text{Symbol}}, where $A$ is the mass number and $Z$ is the atomic number.

Electronic Configuration

The distribution of electrons among various shells (K, L, M, etc.) based on the formula $2n^2$.

Valence Shell

The outermost shell of an atom that contains electrons.

Valency

The combining capacity of an atom, equal to the number of electrons gained, lost, or shared to complete an octet.

Octet

A stable arrangement where the outermost shell of an atom contains $8$ electrons.

Isotopes

Atoms of the same element that have the same atomic number but different mass numbers due to a different number of neutrons.

Unified Atomic Mass Unit (u)

A special unit used to measure the mass of atoms because they are too tiny to be weighed in kilograms or grams.

Weighted Average Atomic Mass

Calculated by multiplying the mass of each isotope by its percent relative abundance and adding the values, such as $35.5\,u$ for Chlorine.

Isobars

Atoms of different elements that have the same mass number but different atomic numbers, such as calcium and argon.

Quantum Mechanical Model

The modern atomic model where electrons do not follow fixed paths but exist as 'electron clouds' around the nucleus.

Homi Jehangir Bhabha

Known as the father of the Indian nuclear programme, he established the Bhabha Atomic Research Centre (BARC).