Introduction: Matter, Energy, and Measurement

Chemistry: The Study of Matter

Chemistry is the scientific discipline concerned with the study of matter, its properties, and the changes it undergoes. It is foundational to understanding processes in biology, physics, environmental science, and many other fields.

• Matter: Anything that has mass and occupies space.

• Properties of Matter: Characteristics that define and distinguish substances.

• Chemical Changes: Transformations that alter the composition of matter.

Classifications of Matter

Matter can be classified by its physical state and composition. Understanding these classifications is essential for identifying and describing substances.

• States of Matter:

  • Solid: Definite shape and volume (e.g., ice).

  • Liquid: Definite volume, takes the shape of its container (e.g., liquid water).

  • Gas: No definite shape or volume (e.g., water vapor).

• Substances:

  • Element: Cannot be decomposed into simpler substances (e.g., oxygen, O2).

  • Compound: Can be decomposed; consists of two or more elements in fixed proportions (e.g., water, H2O).

• Mixtures:

  • Homogeneous Mixture (Solution): Uniform composition throughout (e.g., saltwater).

  • Heterogeneous Mixture: Composition varies throughout (e.g., sand in water).

Atoms, Elements, and Compounds

Atoms are the fundamental building blocks of matter. Elements consist of one type of atom, while compounds are composed of atoms from two or more elements chemically combined.

• Molecules: Groups of atoms bonded together, representing the smallest unit of a compound.

• Law of Constant Composition (Law of Definite Proportions): The composition of a compound is always the same, regardless of the sample.

Representing Elements and Compounds

Chemists use symbols to represent elements. These symbols are typically one or two letters, with the first letter capitalized. Some symbols are derived from Latin or Greek names.

• There are 118 named elements.

• Oxygen is a major component of both the Earth's crust and the human body.

Properties of Matter

Properties of matter are used to identify and classify substances. They are divided into physical and chemical properties, as well as intensive and extensive properties.

• Physical Properties: Can be observed without changing the substance (e.g., color, density, melting point).

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

• Intensive Properties: Independent of the amount of substance (e.g., density, boiling point).

• Extensive Properties: Depend on the amount of substance (e.g., mass, volume).

Physical and Chemical Changes

Changes in matter are classified as physical or chemical. Physical changes do not alter the composition, while chemical changes result in new substances.

• Physical Changes: Changes of state, temperature, or volume (e.g., melting ice).

• Chemical Changes: Formation of new substances (e.g., rusting iron, burning wood).

Separation of Mixtures

Mixtures can be separated by exploiting differences in physical properties of their components.

• Filtration: Separates solids from liquids.

• Distillation: Separates substances based on differences in boiling points.

• Chromatography: Separates substances based on their ability to adhere to a solid surface.

Energy and Its Forms

Energy is the capacity to do work or transfer heat. It exists in two fundamental forms: kinetic and potential energy.

• Kinetic Energy: Energy of motion, dependent on mass and velocity. Equation:

• Potential Energy: Stored energy due to position or arrangement.

• Work: Energy transferred when a force moves an object. Equation:

• Heat: Energy transferred due to temperature difference.

Units of Measurement

Quantitative measurements in chemistry require standardized units. The International System of Units (SI) is used globally.

• SI Base Units:

  • Mass: kilogram (kg)

  • Length: meter (m)

  • Time: second (s)

  • Temperature: kelvin (K)

  • Amount of substance: mole (mol)

  • Volume: derived unit, liter (L) or cubic meter (m3)

• Metric Prefixes: Used to express multiples or fractions of base units (e.g., milli-, centi-, kilo-).

Temperature Scales

Temperature is measured using several scales, with Celsius and Kelvin being most common in science.

• Celsius (°C): 0°C is the freezing point, 100°C is the boiling point of water.

• Kelvin (K): Absolute temperature scale; 0 K is absolute zero. Conversion:

• Fahrenheit (°F): Used in the United States for weather; not common in science. Conversion: Conversion:

Volume and Density

Volume is a derived unit (length3), commonly measured in liters (L) or milliliters (mL). Density is a physical property defined as mass per unit volume.

• Volume: ,

• Density: (mass divided by volume)

Energy Units

The SI unit of energy is the joule (J). The calorie (cal) is also used, especially in nutrition.

• 1 nutritional Calorie (Cal) = 1 kilocalorie (kcal) = 1000 cal

Uncertainty in Measurement

All measurements have some degree of uncertainty due to limitations in instruments and human error. The last digit in a measurement is considered uncertain.

• Exact Numbers: Known with complete certainty (e.g., 12 eggs in a dozen).

• Inexact Numbers: Obtained by measurement; subject to uncertainty.

Precision and Accuracy

Precision and accuracy are important concepts in measurement.

• Precision: How closely repeated measurements agree with each other.

• Accuracy: How closely a measurement agrees with the true value.

Significant Figures

Significant figures reflect the precision of a measured quantity. Rules for determining significant figures:

• All nonzero digits are significant.

• Zeroes between nonzero digits are significant.

• Leading zeroes are not significant.

• Trailing zeroes are significant if there is a decimal point.

When performing calculations:

• Addition/Subtraction: Round to the least significant decimal place.

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

Dimensional Analysis

Dimensional analysis is a method for converting between units using conversion factors. It ensures that calculations are consistent and units cancel appropriately.

• Set up conversion factors so that unwanted units cancel.

• Multiple conversions can be chained together as long as each is an equality.

• Example: To convert inches to centimeters, use .