Chapter 1: Chemistry, Matter, and Measurement

1.1 What is Chemistry?

Chemistry is the central science that studies matter—its composition, properties, and the changes it undergoes. It connects with other sciences such as physics, biology, geology, and medicine.

• Chemistry: The study of matter, its properties, composition, and transformations.

• Matter: Anything that has mass and occupies space.

• Science: The systematic process of learning about the natural universe through observation and experimentation.

The Scientific Method

• Observation: Gathering information about phenomena (e.g., noticing sneezing after visiting a home with a cat).

• Hypothesis: A testable explanation for an observation (e.g., hypothesizing an allergy to cats).

• Experiment: Testing the hypothesis through controlled procedures (e.g., visiting other homes with cats).

• Conclusion: Interpreting results to support or refute the hypothesis.

• Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

Example: If you sneeze after visiting several homes with cats, you may conclude you are allergic to cats.

1.2 The Classification of Matter

Matter can be classified by its physical and chemical properties, composition, and state (phase).

• Physical Properties: Observable without changing the substance's identity (e.g., color, phase, melting point).

• Chemical Properties: Observable only when a substance undergoes a chemical change (e.g., flammability, reactivity).

Classification by Composition

• Pure Substance: Matter with a fixed composition; can be an element (e.g., helium) or a compound (e.g., sodium chloride, NaCl).

• Mixture: Physical combination of two or more substances; can be homogeneous (uniform, e.g., air, sugar water) or heterogeneous (non-uniform, e.g., pasta with sauce, peach pie).

Classification by State (Phase)

• Solid: Definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Definite volume but takes the shape of its container; particles are close but move randomly.

• Gas: No definite shape or volume; particles are far apart and move rapidly, filling the container.

Phase Changes: Physical processes such as melting, boiling, and condensation are reversible and do not change the chemical identity of the substance.

Example: Ice (solid) melts to water (liquid), which boils to steam (gas).

1.3 Measurements

All scientific measurements require both a number and a unit to be meaningful.

• Quantity: Expressed as a number and a unit (e.g., 6 cups, 2 hours).

• Units provide the scale for the measurement and are essential for clarity.

1.4 Expressing Numbers: Scientific Notation

Scientific notation is used to express very large or very small numbers in a concise form.

• Format: , where and is an integer.

• Examples:

  • 400,000 =

  • 0.0004 =

  • 0.0000046 =

• The exponent indicates how many places to move the decimal point.

1.5 Expressing Numbers: Significant Figures

Significant figures (sig figs) reflect the precision of a measured value and indicate the certainty of the measurement.

• Rules for Identifying Significant Figures:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros (before the first nonzero digit) are not significant.

  • Trailing zeros are significant only if there is a decimal point.

• Examples:

  • 0.0250 kg has 3 significant figures.

  • 400,000 g (without a decimal) has 1 significant figure; written as g.

  • 3.00 × 10² m has 3 significant figures.

Rounding and Calculations

• Addition/Subtraction: The answer is rounded to the least precise decimal place among the numbers used.

• Multiplication/Division: The answer has the same number of significant figures as the value with the fewest significant figures.

• Example (Multiplication): (2 sig figs)

• Example (Addition): (rounded to tenths place)

1.6 The International System of Units (SI)

The SI system is the standard for scientific measurements, using base units and prefixes to indicate multiples or fractions of units.

• Base Units: Meter (m) for length, kilogram (kg) for mass, second (s) for time, kelvin (K) for temperature, mole (mol) for amount of substance, ampere (A) for electric current, candela (cd) for luminous intensity.

• Prefixes: Used to indicate multiples or submultiples of units.

• Examples of Equalities:

  • 1 m = 100 cm = cm

  • 1 kg = 1000 g = g

  • 1 L = 1000 mL = mL

  • 1 cm³ = 1 mL = 1 cc

Volume and Density

• Volume: The amount of space occupied by a substance. 1 L = 1000 mL = 1000 cm³.

• Density: The mass per unit volume of a substance.

Formula:

• Units: g/mL, g/cm³

• Example Densities: Water: 1.00 g/mL, Ice: 0.92 g/mL, Aluminum: 2.70 g/mL, Lead: 11.3 g/mL

Energy

• Joule (J): SI unit of energy;

• Calorie (cal): Non-SI unit;

1.7 Converting Units

Unit conversion is essential in chemistry for expressing measurements in different units using conversion factors.

• Conversion Factor: A ratio that expresses how many of one unit are equal to another unit.

• Examples of Equalities:

  • 1 m = 100 cm

  • 1 kg = 2.20 lb

  • 1 L = 1.06 qt

  • 1 cm = 2.54 in.

• Conversion factors can be written as fractions (e.g., or ).

Steps for Unit Conversion

1. Identify the given quantity and units.

2. Determine the needed units.

3. Find the appropriate conversion factor(s).

4. Set up the calculation so that units cancel appropriately.

5. Perform the calculation and round to the correct number of significant figures.

Example: Convert 164 lb to kilograms.

Example: Convert 1.4 days to minutes.

(rounded to 2 sig figs)

Percent as a Conversion Factor

• Percent expresses a ratio of parts to whole and can be used as a conversion factor.

• Example: 18% body fat means

Sample Table: SI Prefixes and Their Multipliers

Additional info: These notes provide foundational concepts for all subsequent topics in General Chemistry, including the use of measurements, units, and the classification of matter, which are essential for understanding chemical reactions, stoichiometry, and laboratory work.