Chemistry Lecture Notes: Scientific Notation, Dimensional Analysis, and Atomic Theory

Vocabulary flashcards covering key concepts from the notes on scientific notation, dimensional analysis, accuracy/precision, and atomic theory.

Scientific notation

A way to write numbers as a × 10^n where 1 ≤ a < 10 and n is an integer, used to express very large or very small numbers.

Significant figures

Digits that carry meaning in a measurement; conversion factors are exact and do not limit the number of significant figures.

Dimensional analysis

A method of converting units by multiplying by conversion factors to cancel old units and obtain the desired units.

Conversion factor

A ratio that expresses two equal quantities used to convert units, e.g., 1 L = 1000 mL or 1 L = 1.0567 qt.

Density

Mass per unit volume (mass/volume); common units are g/mL or g/cm^3; 1 cm^3 equals 1 mL.

Accuracy

How close a measured value is to the true or established value.

Precision

How close multiple measurements are to each other.

Isotope

Atoms of the same element with the same chemical properties but different masses due to different numbers of neutrons.

Atomic number

The number of protons in the nucleus; identifies the element on the periodic table.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Nuclear (isotopic) notation

A representation of an isotope using A (mass number) and Z (atomic number) with the chemical symbol (e.g., 127/53 I).

Electron

A negatively charged subatomic particle located outside the nucleus; very small mass compared to protons and neutrons.

Proton

A positively charged subatomic particle located in the nucleus; mass ≈ 1 amu.

Neutron

A neutrally charged subatomic particle located in the nucleus; mass ≈ 1 amu.

Atomic mass unit (amu)

A unit of mass used for atomic nuclei; defined as 1/12 the mass of a carbon-12 atom.

Electron charge

The fundamental unit of negative electric charge; e = −1.602 × 10^−19 coulombs.

Thomson’s cathode ray experiment

Experiment showing electrons exist and are negatively charged, leading to the discovery of the electron.

Millikan oil drop experiment

Experiment determining the elementary charge e by measuring the charge on tiny oil droplets.

Rutherford’s gold foil experiment

Experiment revealing a tiny, dense, positively charged nucleus because most alpha particles passed through, with some deflections.

Plum pudding model

Early atomic model in which electrons are embedded in a diffuse positive charge (like a fruitcake).

Nucleus

The center of the atom containing protons and neutrons; very small but extremely dense.

Alkali metals

Group 1 metals; highly reactive; typically form +1 ions.

Alkaline earth metals

Group 2 metals; form +2 ions and are highly reactive, though less so than alkali metals.

Halogens

Group 17 nonmetals; highly reactive and commonly form −1 ions; found just to the left of the noble gases.

Noble gases

Group 18 elements; very unreactive gases at room temperature.

Ionic compound

A compound formed by the electrostatic attraction between cations (usually metals) and anions (usually nonmetals); often involves electron transfer.

Dalton’s postulates

Foundational ideas: (1) matter is made of atoms; (2) atoms of an element are identical in mass; (3) compounds are formed by simple whole-number ratios of atoms; (4) atoms are indivisible in chemical reactions; (5) atoms are conserved and rearranged in reactions.

Conservation of mass

In a chemical reaction, mass is neither created nor destroyed; it is conserved.