Introduction to Chemistry

What is Chemistry?

Chemistry is the study of matter, its properties, and the changes it undergoes. It is a central science that connects and enhances our understanding of many other scientific fields, including biology, physics, medicine, and environmental science.

• Matter is anything that has mass and occupies space.

• Chemistry explores the composition, structure, and transformations of matter.

Matter and Its Classification

States of Matter

Matter exists in three primary physical states: solid, liquid, and gas. Each state is characterized by distinct physical properties and particle arrangements.

• Solid: Definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Definite volume but no definite shape; particles are close but can move past one another.

• Gas: No definite shape or volume; particles are far apart and move freely.

Classification by Composition

Matter can be classified based on its composition as either a pure substance or a mixture. This classification helps in identifying and studying different types of matter.

• Pure Substance: Has a fixed composition and distinct properties. Subdivided into elements and compounds.

• Mixture: Composed of two or more substances that retain their individual properties. Can be homogeneous (uniform throughout, also called solutions) or heterogeneous (not uniform throughout).

Elements and Compounds

Elements are substances that cannot be decomposed into simpler substances. Compounds are substances composed of two or more elements in fixed proportions.

• Element: Made of only one kind of atom.

• Compound: Made of atoms of two or more different elements chemically combined.

• Molecule: A group of atoms bonded together, representing the smallest unit of a compound that retains its chemical properties.

Elements in the Earth and Human Body

There are 118 named elements, but only a few are abundant in the Earth's crust and the human body. Oxygen is the most prevalent element in both.

• Five elements make up 90% of the Earth's crust by mass.

• Three elements make up 90% of the human body by mass.

Symbols for Elements

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

Law of Constant Composition

Compounds always have the same relative number of atoms of each element. This is known as the Law of Constant Composition (or Law of Definite Proportions).

• For example, water (H2O) always contains two hydrogen atoms for every one oxygen atom.

Mixtures

Mixtures can be separated into their components by physical means. They can be homogeneous (solutions) or heterogeneous.

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

• Heterogeneous mixture: Non-uniform composition (e.g., granite).

Properties of Matter

Physical and Chemical Properties

Properties of matter are classified as physical or chemical.

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

• Chemical properties: Can only be observed when a substance is transformed into another substance (e.g., flammability).

Intensive and Extensive Properties

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

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

• Extensive properties: Dependent on the amount (e.g., mass, volume).

Physical and Chemical Changes

Changes in matter are either physical or chemical.

• Physical changes: Do not alter the composition of a substance (e.g., melting, boiling).

• Chemical changes: Result in the formation of new substances (e.g., combustion, oxidation).

Separation of Mixtures

Filtration

Filtration separates solid substances from liquids and solutions using a porous barrier.

Distillation

Distillation separates components of a homogeneous mixture based on differences in boiling points.

Chromatography

Chromatography separates substances based on their different abilities to adhere to a solid surface (stationary phase) as a solvent (mobile phase) moves through.

Energy and Its Forms

Definition of Energy

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

• Kinetic energy (KE): Energy of motion, calculated as

• Potential energy: Energy due to position or composition.

Measurement in Chemistry

SI Units and Metric System

Chemistry relies on the International System of Units (SI) for consistency in measurements. Each physical quantity has a base unit.

Metric Prefixes

Prefixes are used to indicate multiples or fractions of base units, making measurements more convenient.

Volume

Volume is a derived unit (from length). Common units include the liter (L) and milliliter (mL). 1 L = 1 dm3; 1 mL = 1 cm3.

Laboratory Glassware for Measuring Volume

Various types of glassware are used to measure and deliver specific volumes of liquids in the laboratory.

Temperature Scales

Temperature is measured using the Celsius, Kelvin, and Fahrenheit scales. The Kelvin scale is the SI unit and has no negative values.

• Celsius to Kelvin:

• Celsius to Fahrenheit:

• Fahrenheit to Celsius:

Energy Units

The SI unit of energy is the joule (J). Historically, the calorie (cal) was used, where 1 cal = 4.184 J. The nutritional Calorie (Cal) is equal to 1 kilocalorie (kcal) or 1000 cal.

Density

Density is a physical property defined as mass per unit volume. It is commonly expressed in g/mL or g/cm3.

• Formula:

Numbers in Chemistry: Accuracy, Precision, and Significant Figures

Exact and Inexact Numbers

Exact numbers are defined or counted values, while inexact numbers are measured and subject to uncertainty.

Accuracy vs. Precision

Accuracy refers to how close a measurement is to the true value, while precision refers to how close repeated measurements are to each other.

Significant Figures

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

• 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.

Significant Figures in Calculations

• For multiplication/division: The result has the same number of significant figures as the measurement with the fewest significant figures.

• For addition/subtraction: The result has the same number of decimal places as the measurement with the fewest decimal places.

Dimensional Analysis and Unit Conversions

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 units cancel, leaving the desired unit.

• Multiple conversions can be chained together as needed.

Practice Problems

• Practice identifying significant figures in measurements.

• Practice converting units using dimensional analysis.

Additional info: For more advanced practice, refer to sample exercises and end-of-chapter problems in your textbook.