Introduction to General Chemistry

Overview

General chemistry is the study of matter, its properties, and the changes it undergoes. This foundational subject introduces students to the classification of matter, physical and chemical properties, measurement systems, and essential calculation techniques used in chemistry.

Classification of Matter

Types of Matter

• Element: The simplest type of matter, composed of only one kind of atom. Examples: gold (Au), oxygen (O2).

• Compound: Matter composed of two or more different elements that are chemically bonded together. Example: water (H2O).

• Mixture: Matter composed of elements and/or compounds that are physically mixed together, not chemically bonded. Examples: air, salad.

Pure substances include elements and compounds, while mixtures can be homogeneous (uniform composition, e.g., saltwater) or heterogeneous (non-uniform, e.g., salad).

Practice Examples

• Homogeneous mixture: Soda, black coffee, saline solution.

• Heterogeneous mixture: Trail mix, fruit salad, orange juice with pulp.

• Element: Gold bar.

• Compound: Ammonia (NH3).

Physical and Chemical Changes

Physical Changes

Physical changes alter the state or appearance of matter without changing its composition. Examples include melting, freezing, dissolving, and breaking.

• Reversible: Most physical changes, such as phase changes (solid ↔ liquid ↔ gas).

Chemical Changes

Chemical changes result in the formation of new substances with different chemical properties. Examples include burning, rusting, and digestion.

• Irreversible: Most chemical changes, such as combustion or cooking.

Practice Examples

• Physical change: Dissolving sugar in water, tearing paper.

• Chemical change: Burning wood, rusting iron, cooking an egg.

Chemical and Physical Properties

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes, forming new substances. These are observed during chemical reactions.

• Examples: Flammability, reactivity with acids, toxicity, radioactivity.

Physical Properties

Physical properties can be observed or measured without changing the substance's chemical identity. These include color, density, melting point, and conductivity.

• Examples: Color, mass, volume, state (solid, liquid, gas), density, melting/boiling point.

Intensive vs. Extensive Properties

Intensive Properties

Intensive properties do not depend on the amount of substance present. They are useful for identifying substances.

• Examples: Density, temperature, boiling point, color, luster.

Extensive Properties

Extensive properties depend on the amount of substance present. They are additive for the same substance.

• Examples: Mass, volume, length, total charge.

Temperature and Heat

Definitions

• Temperature: The average kinetic energy of particles in a substance.

• Heat: The transfer of thermal energy from a hotter object to a cooler one.

Temperature is measured in degrees Celsius (ºC), Fahrenheit (ºF), or Kelvin (K).

• Conversion formulas:

Scientific Notation

Format and Use

Scientific notation expresses very large or small numbers in the form , where and is an integer.

• Positive exponent: Move decimal to the right.

• Negative exponent: Move decimal to the left.

SI Units and Metric Prefixes

SI Base Units

• Mass: kilogram (kg)

• Length: meter (m)

• Time: second (s)

• Temperature: kelvin (K)

• Amount of substance: mole (mol)

• Electric current: ampere (A)

• Luminous intensity: candela (cd)

Metric Prefixes

Metric prefixes indicate multiples or fractions of base units (e.g., kilo-, centi-, milli-).

• Examples: 1 km = 1000 m, 1 mg = 0.001 g

Significant Figures

Rules and Importance

Significant figures (sig figs) reflect the precision of a measurement. The more sig figs, the more precise the value.

• 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.

Calculations with Significant Figures

• Multiplication/Division: Result has as many sig figs as the value with the fewest sig figs.

• Addition/Subtraction: Result has as many decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion Factors

Conversion factors are ratios that relate two units, allowing conversion from one unit to another.

• Example:

Dimensional Analysis

Dimensional analysis is a systematic approach to problem-solving that uses conversion factors to move between units.

• Set up the problem so that units cancel, leaving only the desired unit.

Density

Definition and Formula

Density is the amount of mass per unit volume. It is an intensive property and is calculated as:

• Units: g/cm3 or kg/m3 for solids and liquids; g/L for gases.

Density of Geometric and Non-Geometric Objects

• For regular shapes, use geometric formulas for volume (e.g., ).

• For irregular shapes, use water displacement to find volume.

Summary Table: Classification of Matter

Summary Table: SI Base Units