Atomic Structure and discovery of subatomic particles

Vocabulary flashcards covering the discovery of neutrons, atomic models (Thomson, Rutherford, Bohr), electronic configuration, valency, isotopes, and isobars.

J. Chadwick

The scientist who discovered neutrons by bombarding lighter elements with $\alpha$-particles and observing the emission of neutral particles with mass equal to a proton.

Neutron

A neutral subatomic particle of an atom that has a mass equal to that of a proton but carries zero charge.

Protium

The isotope of the hydrogen atom in which neutrons are absent.

Atomic Mass

The sum of the masses of protons and neutrons in an atom, as the mass of electrons is considered negligible.

Thomson's Atomic Model

Often called the watermelon model, it predicted electrons are embedded in a positive sphere like seeds in a watermelon, explaining the neutrality of the atom.

Rutherford's $\alpha$-Ray Scattering Experiment

An experiment where $\alpha$-rays ($2He^{4+}$) were bombarded upon a thin gold foil to observe particle deflection.

Nucleus

The centrally placed, positively charged region of an atom that contains nearly all its mass and is about $10^{-5}$ times the size of the atom.

Drawback of Rutherford's Model

It could not explain the stability of an atom, as revolving charged electrons should lose energy and eventually fall into the nucleus.

Discrete Orbits

Certain special orbits of electrons allowed inside an atom where electrons do not radiate energy, as proposed in the Bohr's Model.

Bohr's Model Energy Rule

Energy is emitted or absorbed by an atom only when an electron moves from one orbit to another.

Atomic Number ($Z$)

The total number of protons lying in the nucleus of any atom, which defines the identity of the element.

Mass Number ($A$)

The sum of the total number of protons ($n_p$) and neutrons ($n_n$) lying in the nucleus of an atom ($A = n_p + n_n$).

Bohr-Bury Scheme

The rule for the distribution of electrons in various shells, stating that the maximum number of electrons in a shell is given by $2n^2$, where $n$ is the shell number.

Valency

The number of electrons lost or gained by an element to achieve an octet (8 electrons) in its outermost shell.

Isotopes

Atoms of the same element having the same atomic number but different mass numbers, such as ${}^{35}Cl$ and ${}^{37}Cl$.

Uranium Isotope Use

Used as fuel in nuclear reactors.

Cobalt Isotope Use

Used in the treatment of cancer.

Iodine Isotope Use

Used in the treatment of goiter.

Carbon-14 Use

Used in carbon dating to determine the age of organic materials.

Relative Atomic Mass

The average of the masses of all the naturally occurring isotopes of an element, such as $35.5\,u$ for Chlorine.

Isobars

Atoms of different elements that have the same mass number but different atomic numbers, such as ${}^{40}Ca$ and ${}^{40}Ar$.