General Chemistry: Matter, Measurement, Atomic Structure, and Isotopes

Vocabulary practice flashcards covering fundamental chemistry principles including classification of matter, physical/chemical changes, subatomic particles, atomic numbers, isotopes, dimensional analysis, significant figures, and measurement uncertainties.

Atomic Mass Unit (amu)

A unit of mass defined as exactly $\frac{1}{12}$ the mass of one ${^{12}\text{C}}$ atom, equal to $1.660539 \times 10^{-24}\,\text{g}$ (approximately the mass of one proton or neutron).

Mass Spectrometer

An instrument used to measure isotopic weights and isotopic ratios by passing ionized sample gas through accelerating plates and a magnetic field onto a detecting screen.

Atomic Weight

The average atomic mass calculated as the weighted sum of an element's naturally occurring isotopes: $\text{Atomic Weight} = m_1 \times f_1 + m_2 \times f_2 + \dots + m_n \times f_n$, where $m$ is isotopic mass and $f$ is fractional abundance.

Solid

A physical state of matter where particles are held closely together in an ordered fashion; it maintains a fixed shape and volume and does not conform to the shape of its container.

Liquid

A physical state of matter where particles are close together but not held rigidly in position; it has a definite volume and conforms to the shape of its container.

Gas

A physical state of matter where particles have significant separation from each other and move freely, assuming both the shape and volume of their container.

Element

A pure substance that consists of only one kind of atom and cannot be broken down into simpler substances by chemical means.

Compound

A pure substance composed of two or more different elements chemically combined in fixed proportions.

Atom

The smallest quantity or unit of an element that retains the chemical properties of that element.

Molecule

A particle composed of two or more atoms bound together by chemical bonds, which can represent an element (such as $\text{O}_2$) or a compound (such as $\text{H}_2\text{O}$).

Substance

Matter that has a fixed composition and distinct properties, consisting of either a single element or a single compound.

Mixture

A combination of two or more pure substances in variable proportions that can be separated into its components by physical means without altering their chemical identities.

Homogeneous Mixture

A mixture that is uniform in composition and appearance throughout, also referred to as a solution.

Heterogeneous Mixture

A mixture that is non-uniform in composition throughout, containing visually distinguishable components or regions.

Physical Change

A process that alters the physical state or appearance of matter without changing its underlying chemical identity or composition.

Chemical Change

A process involving a change in composition where chemical bonds are broken or formed, transforming original substances into new substances.

Physical Property

A property of a substance that can be observed and measured without changing the chemical identity or composition of the substance.

Chemical Property

A characteristic of a substance that can only be observed as it undergoes a chemical change that alters its composition.

Proton ($p^+$)

A positively charged subatomic particle located in the nucleus of an atom, possessing a mass of approximately $1\,\text{amu}$ ($1.67262 \times 10^{-24}\,\text{g}$) and a charge unit of $+1$.

Neutron ($n^0$)

An electrically neutral subatomic particle located in the nucleus of an atom, possessing a mass of approximately $1\,\text{amu}$ ($1.67493 \times 10^{-24}\,\text{g}$) and a charge unit of $0$.

Electron ($e^-$)

A negatively charged subatomic particle located outside the nucleus of an atom, possessing a mass of $5.4858 \times 10^{-4}\,\text{amu}$ ($9.10938 \times 10^{-28}\,\text{g}$) and a charge unit of $-1$.

Atomic Number ($Z$)

The number of protons in the nucleus of an atom, which uniquely identifies the element.

Mass Number ($A$)

The total sum of protons and neutrons contained within the nucleus of an atom.

Isotopes

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

Cation

A positively charged ion formed when a neutral atom or molecule loses one or more electrons, resulting in fewer electrons than protons.

Anion

A negatively charged ion formed when a neutral atom or molecule gains one or more electrons, resulting in more electrons than protons.

Significant Figures

The meaningful digits in a reported measurement, consisting of all certain digits plus one estimated uncertain digit.

Exact Numbers

Numbers that have defined values (such as unit conversions) or are obtained by counting; they possess an infinite number of significant figures.

Inexact Numbers

Values obtained through physical measurement using an instrument, containing inherent uncertainty in their final reported digit.

Accuracy

An indicator of how close experimental measurements are to the actual or true value.

Precision

An indicator of how close repeated measurements of the same quantity are to one another.

Density

An intensive physical property defined as the ratio of mass to volume: $d = \frac{m}{V}$.

Kelvin Scale

The absolute temperature scale used in chemistry where the lowest possible temperature is absolute zero ($0\,\text{K}$), converted from Celsius by $T_{\text{K}} = T_{{^\circ\text{C}}} + 273.15$.