General Chemistry Exam 1 Study Guide: Matter, Measurement, and Atomic Structure

Matter and Its Classification

States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state is characterized by the arrangement and energy of its particles.

• Solid: Particles are closely packed in a fixed arrangement; solids have definite shape and volume.

• Liquid: Particles are close but can move past one another; liquids have definite volume but take the shape of their container.

• Gas: Particles are far apart and move freely; gases have neither definite shape nor volume.

Example: Water exists as ice (solid), liquid water, and steam (gas) under different conditions.

Classification of Matter

Matter can be classified as pure substances or mixtures. Mixtures are further divided into homogeneous and heterogeneous mixtures.

Pure Substance	Homogeneous Mixture	Heterogeneous Mixture
Has a fixed composition; elements or compounds	Uniform composition throughout; also called solutions	Non-uniform composition; visibly distinct parts
Example: Water (H2O)	Example: Saltwater	Example: Salad

Measurements and Significant Figures

Units and Conversions

Measurements in chemistry use the International System of Units (SI). Common units include meters (m) for length, kilograms (kg) for mass, and liters (L) for volume.

• Conversion factors are used to change from one unit to another.

• Example: $1\;\text{in} = 2.54\;\text{cm}$

Significant Figures

Significant figures reflect the precision of a measurement. When performing calculations, the number of significant figures in the result should reflect the least precise measurement.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros are significant if there is a decimal point.

• Example: 0.00450 has three significant figures.

Scientific Notation

Scientific notation expresses numbers as a product of a coefficient and a power of ten.

• Example: $6,210,000 = 6.21 \times 10^6$

Atoms, Elements, and Isotopes

Atomic Structure

An atom consists of protons, neutrons, and electrons. The number of protons defines the element (atomic number), while the sum of protons and neutrons gives the mass number.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle outside the nucleus.

Isotopic Notation: $^{A}_{Z}\text{X}$, where $A$ is the mass number, $Z$ is the atomic number, and X is the element symbol.

• Example: $^{54}_{24}\text{Cr}$ for chromium with mass number 54 and atomic number 24.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Example: $^{12}\text{C}$ and $^{14}\text{C}$ are isotopes of carbon.

Density and Calculations

Density

Density is the mass per unit volume of a substance.

• Formula: $d = \frac{m}{V}$

• Units: g/cm3 or kg/m3

• Example: If a sample has a mass of 22.6 g and a volume of 1.04 cm3, its density is $d = \frac{22.6\;\text{g}}{1.04\;\text{cm}^3} = 21.7\;\text{g/cm}^3$

Temperature Conversions

Temperature can be measured in Celsius (°C), Kelvin (K), or Fahrenheit (°F). The Kelvin scale is the SI unit for temperature.

• Formulas:

  • $K = ^\circ C + 273.15$

  • $^\circ F = 1.8(^\circ C) + 32$

• Example: To convert 2375°F to Kelvin: First convert to Celsius, then to Kelvin.

Problem Solving and Dimensional Analysis

Dimensional Analysis

Dimensional analysis (factor-label method) is used to convert between units using conversion factors.

• Example: To convert 2.42 carats to kilograms, use the conversion $1\;\text{carat} = 0.2\;\text{g}$ and $1000\;\text{g} = 1\;\text{kg}$.

Common Conversion Factors

Quantity	Conversion
Length	1 in = 2.54 cm
Mass	1 lb = 453.6 g
Volume	1 L = 1.06 qt

Practice with Significant Figures and Scientific Notation

• When multiplying or dividing, the result should have the same number of significant figures as the measurement with the fewest significant figures.

• When adding or subtracting, the result should have the same number of decimal places as the measurement with the fewest decimal places.

• Example: $13.912 + 2.00 = 15.91$ (rounded to two decimal places)

Periodic Table and Elements

Periodic Table Organization

The periodic table arranges elements by increasing atomic number. Elements in the same group (column) have similar chemical properties.

• Metals, Nonmetals, Metalloids: Metals are on the left, nonmetals on the right, and metalloids border the staircase line.

• Diatomic Elements: Elements that exist as molecules of two atoms: H2, N2, O2, F2, Cl2, Br2, I2.

Sample Problems and Applications

• Calculate the mass, volume, or density of a substance using the appropriate formula.

• Convert between units using dimensional analysis and conversion factors.

• Identify the number of protons, neutrons, and electrons in an atom or ion.

• Classify matter as pure substances, homogeneous mixtures, or heterogeneous mixtures.

• Apply significant figure rules to calculations and express answers in scientific notation.

Formula Sheet Reference

• Density: $d = \frac{m}{V}$

• Temperature: $K = ^\circ C + 273.15$

• Atomic Weight: $\text{Atomic weight} = \sum (\text{isotope mass} \times \% \text{abundance})$

• Percent Yield: $\%\;\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$

Additional info: This guide is based on a sample exam covering topics from the first chapter of a General Chemistry course, including matter, measurement, significant figures, atomic structure, and basic calculations. The formula sheet and periodic table are standard references for such exams.