Atomic Structure and Early Atomic Models

Comprehensive vocabulary flashcards covering historical atomic models, experimental discoveries, subatomic particles, and key scientists from early modern chemistry.

John Dalton

Known as the 'Father of the Modern Atomic Theory,' he proposed the Billiard Ball model, believed that atoms were indestructible and homogenous particles, and stated that compounds form when atoms of two or more elements combine in whole-number ratios (Definite Proportions).

Billiard Ball Model

The early atomic model proposed by John Dalton that conceptualized the atom as an indivisible, uniform, and indestructible solid sphere.

William Crookes

Scientist who in 1879 constructed an evacuated cathode ray tube that produced a stream of electrons, showing luminescence on a zinc sulfide screen.

Cathode Ray Tube

An evacuated tube with a stream of electrons deflected by a magnetic field, providing experimental evidence that atoms contain charged subatomic particles.

J.J. Thomson

Scientist who first discovered the electron ($e^-$) using cathode ray tube deflection and suggested that atoms are heterogeneous, consisting of negative particles dispersed within a solid, positive matrix.

Plum Pudding Model

Also referred to as the Blueberry Muffin atom, this atomic model proposed by J.J. Thomson depicted negative electrons embedded within a positively charged 'pudding' matrix.

Lord Rutherford

Scientist who discovered the proton ($p^+$) and in 1911 formulated the nuclear model of the atom based on the results of his Gold Foil Experiment.

Gold Foil Experiment

An experiment in which gold foil was bombarded with alpha particles; while most passed through undeflected, a few scattered at large angles, demonstrating that atoms are mostly empty space with a small, dense, positively charged nucleus.

Nucleus

The small, massive, positively charged central region of an atom discovered by Rutherford, surrounded by empty space.

Niels Bohr

Scientist who proposed in 1913 that electrons inhabit distinct circular energy levels or orbits outside the nucleus so that atoms do not collapse upon themselves, explaining atomic spectra.

Marie Curie

The scientist who discovered radioactivity.

James Chadwick

The scientist who discovered the neutron in 1932.

Alpha Particles

Radioactive particles emitted by an $\alpha$-source, used in Rutherford's experiment to bombard gold foil and reveal the existence of dense atomic nuclei.

Proton ($p^+$)

A positively charged subatomic particle located in the nucleus, discovered by Rutherford, with a relative charge of $+1$ and a relative mass of $1.00728\,\text{amu}$.

Electron ($e^-$)

A negatively charged subatomic particle discovered by J.J. Thomson, located outside the nucleus, with a relative charge of $-1$, a relative mass of $0.00055\,\text{amu}$, or approximately $\frac{1}{2000}$ that of a proton.

Neutron

A neutral subatomic particle located in the nucleus, discovered by Chadwick in 1932, possessing a relative charge of $0$ and a relative mass of $1.00867\,\text{amu}$.

Neutral Atom

An atom whose net charge is zero because its number of protons equals its number of electrons ($\#\,p^+ = \#\,e^-$).

Ion

A charged particle formed when an atom loses or gains electrons.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Isotopes

Particles or atoms of the same element that share the same Atomic Number but possess different Atomic Masses.

Law of Definite Proportions

A foundational chemical principle proposed by John Dalton stating that compounds form when atoms of two or more elements combine in whole-number ratios.