Introduction to General Chemistry

Matter and Its Classification

Chemistry is the study of matter and its changes. Understanding how matter is classified and how it behaves is fundamental to general chemistry.

• Matter: Anything that occupies space and has mass.

• Classification of Matter:

  • Pure Substance: Composed of only one kind of atom or molecule. Examples: Gold (Au), Water (H2O).

  • Mixture: Composed of two or more different elements or compounds physically mixed together.

    • Homogeneous Mixture: Uniform composition throughout. Example: Salt water.

    • Heterogeneous Mixture: Non-uniform composition. Example: Salad, Salsa.

Example: Crystalline sugar is a pure substance; salsa is a heterogeneous mixture.

Physical and Chemical Changes

Matter can undergo changes that are either physical or chemical in nature.

• Physical Changes: Alter the physical state or appearance without changing chemical composition. Examples: Melting, Boiling, Dissolving sugar in water.

• Chemical Changes: Result in the formation of new substances with new chemical bonds and properties. Examples: Burning wood, Cooking an egg, Rusting iron.

Phase Changes: Reversible and Irreversible

Phase changes can be classified as reversible or irreversible depending on whether the original state can be restored.

• Reversible Changes: Can be undone to restore the original structure. Example: Dissolving sugar in water (can be reversed by evaporation).

• Irreversible Changes: Cannot be undone. Example: Cooking an egg.

Chemical and Physical Properties

Properties of matter are used to describe and identify substances.

• Chemical Properties: Observed during a chemical reaction; describe how a substance interacts with other substances. Examples: Reactivity with acids, Flammability, Oxidation.

• Physical Properties: Can be observed without changing the chemical identity. Examples: Color, Melting point, Density, State at room temperature.

Intensive vs. Extensive Properties

Properties of matter can be classified based on their dependence on the amount of substance present.

• Intensive Properties: Do not depend on the amount of substance. Examples: Density, Melting point, Color.

• Extensive Properties: Depend on the size or amount of substance. Examples: Mass, Volume, Length.

Phase Changes and Bonding

SI Units and Measurements

SI Base Units

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

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: The sum of kinetic and potential energies of all atoms in an object.

• Temperature: The average kinetic energy of an object.

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

Temperature Conversions

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 factors are used to relate different units and perform calculations.

• 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 a physical property that relates mass and volume.

• Definition: Density is the amount of mass per unit volume.

• 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.

Summary Table: Intensive vs. Extensive Properties

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.