Unit 2: Density, Atomic Theory & Nuclear Chemistry Flashcards

Vocabulary flashcards covering density, specific gravity, properties and separation of matter, atomic theory development, subatomic particles, radioactivity, nuclear decay, binding energy, half-life, fusion, fission, and nuclear reactors.

Density

The mass per unit volume of a substance, represented by the symbol $D$ (or $\rho$) and calculated using the formula $D = \frac{m}{V}$.

Specific Gravity

The measure of the mass of an object compared to the mass of an equal volume of water, calculated as $\text{sp. gr.} = \frac{\text{Density of object}}{\text{Density of water}}$; it is a dimensionless quantity equal to density without units.

Absolute Error ($E_a$)

The difference between an observed experimental value ($O$) and an accepted true value ($A$), given by the formula $E_a = O - A$.

Relative Error ($E_r$)

The percentage error of a measurement relative to the accepted value, calculated as $E_r = \frac{E_a}{A} \times 100 = \frac{O - A}{A} \times 100$.

Accuracy

The closeness of an experimental measurement or calculation to the true or accepted value.

Precision

The degree of agreement, consistency, or repeatability among a set of experimental measurements.

Element

A pure substance in which all of the atoms contain the same number of protons in the nucleus.

J.J. Berzelius

The Swedish chemist generally credited with creating the modern system of chemical symbols for elements.

Compound

A pure substance composed of two or more different elements chemically bonded to one another.

Mixture

A physical combination of two or more pure substances that are physically joined rather than chemically combined.

Alloy

A homogeneous mixture of two or more metals, such as brass ($\text{Cu} + \text{Zn}$) or bronze ($\text{Cu} + \text{Sn}$).

Homogeneous Mixture

A mixture that has a uniform and constant composition throughout, also referred to as a solution.

Heterogeneous Mixture

A mixture that has a non-uniform, varying composition with visually distinct components.

Physical Property

A feature or characteristic of a substance (such as density, specific gravity, hardness, odor, or boiling point) that distinguishes it without changing its chemical identity.

Chemical Property

A characteristic describing the ability of a substance to form other substances by undergoing specific chemical reactions under given conditions.

Physical Change

A change in which the composition of a substance is not altered and the substance retains its original identity.

Chemical Change

A process in which a substance loses its identity and transforms into a new substance with new chemical and physical properties.

Distillation

A physical separation process in which a liquid is boiled to produce a vapor that is then condensed back into a liquid, taking advantage of different boiling points.

Paper Chromatography

A laboratory method used to separate components of mixtures, such as ink dyes, as they migrate across paper.

Decanting

A physical separation technique involving pouring off a top liquid layer to separate it from a solid sediment or another liquid.

Democritus

The Greek philosopher (400 B.C.) who proposed that matter is composed of tiny indivisible particles called "atomos".

Law of Conservation of Mass

A principle formulated by Antoine Lavoisier (1789) stating that mass is neither created nor destroyed during a chemical reaction.

Law of Definite Proportions

A principle established by Joseph Proust (1799) stating that a given chemical compound always contains its component elements in fixed proportions by mass.

Law of Multiple Proportions

A law formulated by John Dalton stating that when two elements form multiple compounds, the ratio of the masses of the second element that combine with a fixed mass of the first are small whole numbers.

Dalton's Atomic Theory

A scientific theory re-proposed in 1808 by John Dalton, stating that elements consist of small indivisible atoms, atoms of an element are identical, and chemical reactions involve whole-number rearrangements of atoms.

Cathode Ray Tube (CRT)

A sealed glass tube apparatus used by J.J. Thomson to demonstrate that cathode rays consist of negatively charged subatomic particles called electrons.

Thomson Model of the Atom

The atomic model (Plum Pudding Model) proposed by J.J. Thomson depicting the atom as a sphere of uniform positive charge with negatively charged electrons embedded inside.

Robert A. Millikan

The scientist who determined the exact charge ($-1.60 \times 10^{-19}\,\text{C}$) and mass ($9.10 \times 10^{-28}\,\text{g}$) of an electron using the oil drop experiment.

Rutherford Model of the Atom

The atomic model derived by Ernest Rutherford from the gold foil alpha-scattering experiment, proving that the atom contains a tiny, dense, positively charged nucleus surrounded mostly by empty space.

Proton ($p^+$)

A positively charged nucleon located in the nucleus, discovered by Ernest Rutherford, having a relative mass of $1$, charge of $+1.6022 \times 10^{-19}\,\text{C}$, and composed of three quarks ($u, u, d$).

Electron ($e^-$)

A negatively charged subatomic particle discovered by J.J. Thomson, located outside the nucleus in energy levels, with a relative charge of $-1$ and a mass of $9.11 \times 10^{-28}\,\text{g}$.

Neutron ($n^0$)

A neutral subatomic particle located in the nucleus, discovered by James Chadwick in 1932, having a relative mass of $1$ and composed of three quarks ($u, d, d$).

Atomic Number ($Z$)

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

Mass Number ($A$)

The total number of protons plus neutrons (nucleons) in an atomic nucleus.

Isotopes

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

Ions

Charged atoms or groups of atoms that have gained or lost electrons.

Radioactivity

The spontaneous emission of particles or electromagnetic radiation from an unstable atomic nucleus, discovered by Henri Becquerel in 1896.

Alpha Particle ($\alpha$)

A helium nucleus ($^{4}_{2}\text{He}$) emitted during nuclear decay, consisting of two protons and two neutrons; it has low penetrating power and can be stopped by paper.

Beta Particle ($\beta^-$)

A high-speed electron ($^{0}_{-1}\text{e}$) ejected from an atomic nucleus when a neutron spontaneously transforms into a proton.

Positron ($\beta^+$)

A positively charged particle ($^{0}_{+1}\text{e}$) ejected from a nucleus when a proton spontaneously transforms into a neutron.

Gamma Ray ($\gamma$)

A high-energy photon ($^{0}_{0}\gamma$) emitted when an excited atomic nucleus drops to a lower energy state; it possesses very high penetrating power.

Electron Capture

A nuclear process in which an inner-shell electron falls into the nucleus, combining with a proton to form a neutron.

Mass Defect

The difference between the total calculated mass of individual subatomic particles and the smaller actual mass of the bound nucleus.

Nuclear Binding Energy

The energy required to break up a nucleus into its component nucleons, converted from mass defect according to Einstein's equation $E = mc^2$.

Half-Life ($t_{1/2}$)

The average time required for one-half of the unstable radioactive atoms in a sample to decay.

Transmutation

The conversion of an atom of one element into an atom of another element through nuclear bombardment or radioactive decay.

Nuclear Fusion

A reaction in which smaller atomic nuclei combine at extremely high temperatures to form a larger, more stable nucleus, releasing energy.

Nuclear Fission

The splitting of a heavy atomic nucleus into two smaller nuclei along with one or more neutrons and energy.

Critical Mass

The minimum mass of fissionable material needed to sustain a self-sustaining nuclear chain reaction.

Control Rods

Rods composed of materials such as cadmium or boron inserted into a nuclear reactor core to absorb neutrons and regulate or stop the fission reaction.

Moderator

A substance in a nuclear reactor (such as graphite or heavy water, $\text{D}_2\text{O}$) used to slow down fast neutrons to sustain the chain reaction.

Breeder Reactor

A nuclear reactor designed to convert non-fissionable material into fissionable material (such as Plutonium-239 from Uranium-238) at a faster rate than it consumes fuel.