Introduction to General Chemistry

Matter and Its Classification

Chemistry is the study of matter and its changes. Matter is anything that occupies space and has mass. Understanding how matter is classified is fundamental to general chemistry.

• Pure Substance: Composed of only one kind of atom or molecule. Examples include gold (Au) and water (H2O).

• Mixture: Contains two or more different elements or compounds physically mixed. Mixtures can be:

  • Homogeneous Mixture: Uniform composition throughout (e.g., salt water).

  • Heterogeneous Mixture: Non-uniform composition (e.g., salad, salsa).

• Element: Pure substance made of one type of atom (e.g., oxygen (O2)).

• Compound: Pure substance made of two or more types of atoms chemically bonded (e.g., water (H2O)).

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical, depending on whether the chemical identity is altered.

• Physical Changes: Alter the physical state without changing chemical composition. Examples: melting, boiling, dissolving sugar in water.

• Chemical Changes: Result in new substances with new chemical bonds and properties. Examples: burning wood, cooking an egg, rusting iron.

Phase Changes: Reversible and Irreversible

• Reversible Changes: Can be undone to restore the original structure (e.g., melting, freezing, boiling, dissolving sugar in water).

• Irreversible Changes: Cannot be undone (e.g., burning, cooking an egg).

Chemical and Physical Properties

Properties of matter are used to identify and classify substances.

• Chemical Properties: Observed during a chemical reaction; describe how a substance interacts with others. Examples: reactivity with acids, flammability, oxidation.

• Physical Properties: Can be observed without changing chemical identity. Examples: color, melting point, density, state at room temperature.

Intensive vs. Extensive Properties

• Intensive Properties: Do not depend on the amount of substance present. Examples: density, melting point, color.

• Extensive Properties: Depend on the size or amount of substance present. Examples: mass, volume, length.

SI Units and Measurements

SI Base Units

The International System of Units (SI) provides standard units for physical quantities in science.

Perimeter, Area, and Volume

• Area (A):

• Volume (rectangular):

• Volume (cylinder):

Metric Prefixes

Metric prefixes indicate multiples or fractions of base units.

• Example: To convert 654 kg to g, multiply by .

Temperature and Scientific Notation

• Thermal Energy: Sum of kinetic and potential energies of all atoms in an object.

• Temperature: Average kinetic energy of an object.

• Scientific Notation: Format: , where is the coefficient and is the exponent.

• Example:

Significant Figures

Significant figures reflect the precision of a measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a decimal number are significant.

Significant Figures in Calculations

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

Conversion Factors and Dimensional Analysis

• Conversion Factor: Ratio that relates two different units. Example:

• Dimensional Analysis: Method for converting units using conversion factors:

  1. Write the given amount.

  2. Multiply by conversion factors to cancel units.

  3. Arrive at the desired unit.

Density and Measurement

Density

Density is the amount of mass per unit volume. It is a key property for identifying substances and solving measurement problems.

• Formula:

• Units: g/cm3 for solids and liquids, g/L for gases.

Density of Geometric Objects

• Calculate volume using geometric formulas, then use density to find mass or vice versa.

• Example (cube): , where is the length of a side.

Density by Water Displacement

• For irregular objects, volume can be measured by the amount of water displaced.

• Example: If water rises from 200 mL to 265 mL, the object's volume is 65 mL.

Additional info: These notes cover foundational concepts in General Chemistry, including matter classification, physical and chemical changes, properties, measurement, SI units, scientific notation, significant figures, conversion factors, dimensional analysis, and density. Practice questions and examples are included to reinforce understanding.