Chemistry Unit Review: Measurement, Dimensional Analysis, Atomic Structure, and Periodic Trends

Vocabulary practice flashcards covering significant figure rules, mathematical operations, dimensional analysis, periodic trends, and electromagnetic atomic energy levels.

Certain Digits

All the numbers recorded directly from the markings on a measuring instrument, excluding the final estimated value.

Estimated Digit

The final digit recorded in a measurement that is approximated one place beyond the smallest graduation mark of the device (such as the $0$ in a reading of $56.0\,\text{mL}$).

Exact Number

A quantity that has no uncertainty and therefore contains an infinite number of significant figures, such as counted objects ($25\text{ people}$) or defined conversions ($12\,\text{in} = 1\,\text{ft}$).

Leading Zeros

Zeros placed to the left of all non-zero digits; they are never counted as significant figures (e.g., $0.003$ has $1$ significant figure).

Captive Zeros

Zeros located between non-zero digits; they are always counted as significant figures (e.g., $205$ has $3$ significant figures).

Trailing Zeros

Zeros situated at the end of a number; they are significant only if the number contains a written decimal point, but are not significant if no decimal point is shown.

Significant Figure Rule for Addition and Subtraction

A calculation rule requiring the final answer to be rounded to the same number of decimal places as the starting measurement with the fewest decimal places.

Significant Figure Rule for Multiplication and Division

A calculation rule requiring the final answer to be rounded to the same total number of significant figures as the starting measurement with the least significant figures.

Dimensional Analysis

A structured mathematical method used in chemistry to convert from one unit of measurement to another by canceling out unwanted units using conversion factors.

Conversion Factor

A ratio of equivalent quantities expressed in different units used to change the units of a measured quantity (e.g., $1\,\text{in} = 2.54\,\text{cm}$ or $1\,\text{mi} = 5{,}280\,\text{ft}$).

Base Units

The standard fundamental metric measurement units: grams ($\text{g}$) for mass, liters ($\text{L}$) for volume, and meters ($\text{m}$) for length.

Metric Prefixes

Prefixes used to scale base units: Mega- ($\text{M}$, $1{,}000{,}000$), Kilo- ($\text{k}$, $1{,}000$), Deci- ($\text{d}$, $0.10$), Centi- ($\text{c}$, $0.010$), Milli- ($\text{m}$, $0.0010$), and Micro- ($\mu$, $1 \times 10^{-6}$).

Atomic Radius

One-half ($\frac{1}{2}$) of the distance between the nuclei of two identical, bonded or touching atoms ($2r$).

Shielding Effect

The effect in which inner core electrons block or reduce the positive nuclear charge attraction experienced by outer valence electrons.

Periodic Trend for Atomic Radius

Atomic size decreases from left to right across a period due to increased nuclear charge pulling electrons inward, and increases down a group due to the addition of occupied energy levels.

Ionization Energy ($\text{I.E.}$)

The amount of energy required to remove an electron from a gaseous atom (e.g., $\text{Li}_{(g)} \rightarrow \text{Li}^{+}_{(g)} + \text{e}^{-}$).

Successive Ionization Energies

The stepwise energies required to remove consecutive electrons ($\text{1st I.E.} < \text{2nd I.E.} < \text{3rd I.E.}$), which display a very large increase when an inner core electron is removed from an ion isoelectronic with a noble gas.

Periodic Trend for Ionization Energy

Ionization energy increases across a period from left to right due to increased effective nuclear charge, and decreases down a group because valence electrons are located further from the nucleus.

Cation

A positively charged ion formed when an atom loses electrons; it is always smaller in radius than its neutral atom due to reduced electron repulsions and possible loss of an energy level.

Anion

A negatively charged ion formed when an atom gains electrons; it is always larger in radius than its neutral atom due to increased electron repulsions weakening nuclear attraction.

Electronegativity ($\text{E.N.}$)

The tendency of an atom to attract electrons when chemically combined with another element, ranging from a low of $0.7$ to a high of $4.0$ for Fluorine.

The Upside-Down Snowman

A visual mnemonic used to remember periodic trends: both electronegativity and ionization energy decrease moving down a group and increase moving across a period from left to right.

Ground State

The lowest, normal, and most stable energy state of an electron in an atom, situated closest to the nucleus.

Excited State

A temporary and unstable high-energy state where an electron has absorbed energy and jumped to an orbital further from the nucleus.

Photon Emission (Light Production)

The release of electromagnetic radiation (light) produced when an excited electron falls back down to a lower, more stable energy level.

Electromagnetic Spectrum Trend

The relationship across electromagnetic radiation where shorter wavelength corresponds to higher frequency and higher energy, while longer wavelength corresponds to lower frequency and lower energy.

Accuracy

A measure of how close an experimental value or average of a data set is to the correct, true, or accepted value.

Precision

A measure of how close individual measurements in a repeated set of trials are to one another, reflecting repeatability.

Isoelectronic

A state in which two or more chemical species (atoms or ions) possess the exact same number of electrons and identical electron configurations.