Introduction to Chemistry

What is Chemistry?

Chemistry is the scientific study of matter and the changes it undergoes. Matter encompasses everything that can be weighed and occupies space, forming the material basis of the universe. Chemists seek to classify matter and identify its properties to better understand the natural world.

• Matter: Anything that has mass and takes up space.

• Property: A unique characteristic used to identify or describe matter.

Classifying Matter

Physical States of Matter

Matter exists in different physical states, primarily as solids, liquids, and gases. Each state is characterized by distinct properties related to particle arrangement and behavior.

• Volume

• Motion

• Compressibility

• Flow (pouring ability)

Properties of Solids

• Shape: Fixed and ordered; particles are close together, often forming a crystalline arrangement.

• Motion: Particles vibrate but do not move past each other.

• Compressibility: Non-compressible; volume does not change with pressure.

• Flow: Solids cannot flow or be poured.

• Example: Table salt (NaCl) crystals.

Properties of Liquids

• Shape: Not defined; liquids take the shape of their container.

• Volume: Well defined.

• Motion: Particles move randomly but less freely than in gases.

• Compressibility: Non-compressible.

• Flow: Liquids can flow and be poured due to intermolecular forces allowing particles to slide past each other.

• Example: Water.

Properties of Gases

• Shape and Volume: Gases assume both the shape and volume of their container; particles are far apart.

• Motion: Particles move rapidly and randomly.

• Compressibility: Gases are compressible; volume decreases under pressure.

• Flow: Gases do not pour like liquids.

• Example: Air.

Chemical Composition: Substances and Mixtures

Matter can also be classified by its chemical composition as substances or mixtures.

• Substances: Pure materials with a fixed composition; can be elements or compounds.

• Mixtures: Physical combinations of two or more substances; composition can vary.

Types of Substances

• Element: A substance that cannot be broken down into simpler substances by chemical means. Elements are listed on the periodic table (e.g., Hydrogen (H), Lithium (Li)).

• Compound: A substance formed from two or more elements in a fixed ratio, with properties different from its constituent elements (e.g., Water, ).

Types of Mixtures

• Homogeneous Mixture: Uniform composition throughout (e.g., black coffee).

• Heterogeneous Mixture: Non-uniform composition (e.g., orange juice with pulp).

Separation of Substances and Mixtures

• Mixtures: Can be separated by physical means (e.g., filtration, distillation).

• Substances: Can only be separated by chemical means (e.g., electrolysis of water).

Physical and Chemical Properties & Changes

Physical Properties

Physical properties can be measured or observed without changing the chemical composition of a substance.

• Examples: Mass, volume, temperature, color, density, boiling point, freezing point.

• Intensive Properties: Independent of sample size (e.g., temperature, density).

• Extensive Properties: Dependent on sample size (e.g., volume, mass).

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes.

• Examples: Flammability, combustibility, explosiveness, toxicity, corrosiveness.

Physical vs Chemical Changes

• Physical Change: Alters the physical state or appearance without changing chemical composition (e.g., melting, boiling, breaking glass).

• Chemical Change: Results in the formation of new substances (e.g., rusting iron, burning wood).

Units of Measurement

SI Base Units

Scientific measurements use standardized units, primarily the International System of Units (SI).

Scientific Notation and Metric Prefixes

Scientific notation expresses numbers as a product of a single digit and a power of ten, making it easier to handle very large or small values.

• Format: where is and is the exponent.

• Example:

Metric Prefixes

Significant Figures

Definition and Importance

Significant figures are the meaningful digits in a measured or calculated quantity, reflecting the precision of the measurement.

• Includes all known digits plus one estimated digit.

• Indicates the reliability and precision of data.

Rules for 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.

Significant Figures in Calculations

• Addition/Subtraction: Result is limited by the least number of decimal places.

• Multiplication/Division: Result is limited by the number with the least significant figures.

Dimensional Analysis

Conversion Factors

Dimensional analysis uses conversion factors to convert between units. Conversion factors are ratios expressing equivalence between units (e.g., ).

• Exact numbers have no uncertainty and do not limit significant figures.

• Inexact numbers (measured values) have uncertainty.

Steps for Dimensional Analysis

1. Identify starting and desired units.

2. Select the correct conversion factor.

3. Arrange conversion so units cancel appropriately.

4. Check if the result is reasonable.

Derived Units: Volume and Density

Volume

• SI unit: cubic meter ()

• Common units: liter (L), milliliter (mL)

• 1 L = 1000 mL

Density

Density is an intensive property defined as mass per unit volume.

• Formula:

• Used to identify substances and calculate mass or volume.

• Example: A cube with side length 1.50 cm and mass 9.20 g has density

Temperature Conversions

• Fahrenheit to Celsius:

• Celsius to Kelvin:

Summary and Study Tips

• Review lecture slides and notes regularly.

• Practice homework problems and textbook examples.

• Utilize tutoring centers and supplemental instruction.

• Understand concepts, not just memorize facts.

Additional info: Some content inferred and expanded for completeness, including full tables and formulas, based on standard General Chemistry curriculum.