Physics 414: Atoms - Models and Spectra

Vocabulary flashcards defining key atomic models, spectral properties, and postulates of the Bohr model as described in the Physics 414 lecture notes.

Plum pudding model

The first model of the atom proposed by J. J. Thomson in 1898, where positive charge is uniformly distributed throughout the volume and negatively charged electrons are embedded in it like seeds in a watermelon.

Nucleus

A small volume at the centre of an atom where the entire positive charge and most of the mass is concentrated, discovered by Ernest Rutherford through $\alpha$-particle scattering experiments.

Impact parameter ($b$)

The perpendicular distance of the initial velocity vector of an $\alpha$-particle from the centre of the nucleus.

Emission line spectrum

A spectrum consisting of bright lines on a dark background, produced by radiation from rarefied gases where individual atoms emit certain discrete wavelengths.

Absorption spectrum

A spectrum containing dark lines that correspond precisely to the wavelengths an element would normally emit, produced when white light passes through a gas.

Spectral series

Sets of lines in the hydrogen spectrum whose spacing decreases in a regular way, including the Lyman, Balmer, Paschen, Brackett, and Pfund series.

Balmer series

The first observed spectral series of hydrogen located in the visible region, described by the formula $\frac{1}{\lambda} = R \left( \frac{1}{2^2} - \frac{1}{n^2} \right)$ for $n = 3, 4, 5...$

Rydberg constant ($R$)

A physical constant appearing in the formulas for spectral series with an empirical value of approximately $1.097 \times 10^7\,\text{m}^{-1}$.

Stationary states

Definite stable orbits proposed by Bohr in which an electron can revolve without the emission of radiant energy.

Bohr's second postulate

The quantization condition stating that an electron revolves only in orbits for which the angular momentum ($L$) is an integral multiple of $\frac{h}{2\pi}$, expressed as $L = \frac{nh}{2\pi}$.

Bohr radius ($a_0$)

The size of the innermost orbit ($n = 1$) of a hydrogen atom, which is approximately $5.29 \times 10^{-11}\,\text{m}$.

Ground state

The lowest energy state of an atom ($n = 1$), which for hydrogen corresponds to an energy of $-13.6\,\text{eV}$.

Excited state

A state of higher energy into which an atom is raised from its ground state through processes like electron collisions or photon absorption.

Ionisation energy

The minimum energy required to free an electron from the ground state of an atom; for a hydrogen atom, this is $13.6\,\text{eV}$.

Hydrogenic atoms

Atoms consisting of a nucleus with positive charge $+Ze$ and a single electron, such as hydrogen, singly ionised helium ($He^+$), and doubly ionised lithium ($Li^{++}$).

Distance of closest approach ($d$)

The centre-to-centre distance between an $\alpha$-particle and a nucleus when the particle momentarily stops and reverses direction, where its initial kinetic energy equals the electric potential energy.

De Broglie's explanation of quantization

The theory that electrons in circular orbits form resonant standing waves, requiring the circumference of the orbit to be an integral number of de Broglie wavelengths ($2\pi r_n = n\lambda$).

LASER

An acronym for Light Amplification by Stimulated Emission of Radiation, which produces light with high phase correlation, minimal divergence, and high intensity.