Introduction to Chemistry

What is Chemistry?

Chemistry is the study of matter, its properties, and the changes it undergoes. It is central to our understanding of many science-related fields, including biology, physics, medicine, and environmental science.

• Matter: Anything that has mass and occupies space.

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

Classification of Matter

States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state is defined by the arrangement and movement of its particles.

• Solid: Definite shape and volume; particles are closely packed.

• Liquid: Definite volume but no definite shape; particles are less tightly packed than in solids.

• 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 substances (elements and compounds) or mixtures (homogeneous and heterogeneous).

• Element: A substance that cannot be decomposed into simpler substances. Made of one kind of atom.

• Compound: A substance composed of two or more elements chemically combined in fixed proportions.

• Mixture: A combination of two or more substances in which each retains its own identity and properties.

Atoms and Molecules

Atoms are the fundamental building blocks of matter. Molecules are groups of atoms bonded together, representing the smallest unit of a compound that retains its chemical properties.

• Atoms: Smallest unit of an element.

• Molecules: Two or more atoms bonded together.

Law of Constant Composition (Law of Definite Proportions)

Compounds always have the same relative number of atoms of each element. This means that any sample of a compound will have the same composition by mass.

• Example: Water (H2O) always contains two hydrogen atoms for every one oxygen atom.

Mixtures: Homogeneous and Heterogeneous

Mixtures can be classified based on uniformity:

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

• Heterogeneous Mixture: Composition varies from one region to another (e.g., granite).

Classification Flowchart

A decision scheme can be used to classify matter as an element, compound, homogeneous mixture, or heterogeneous mixture.

Properties of Matter

Physical and Chemical Properties

Properties of matter are divided into physical and chemical properties:

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

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

Intensive and Extensive Properties

Properties can also be classified as intensive or extensive:

• 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 Change: Does not alter the composition (e.g., melting, boiling).

• Chemical Change: Alters the composition, resulting in new substances (e.g., combustion, oxidation).

Separation of Mixtures

Physical Methods of Separation

Mixtures can be separated into their components by exploiting differences in physical properties:

• 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

Definition and Types of Energy

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

• Kinetic Energy: Energy of motion, given by the equation:

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

Measurement in Chemistry

SI Units and Metric System

Chemistry relies on quantitative measurements, which require standardized units. The International System of Units (SI) is used globally.

Metric Prefixes

Prefixes are used to indicate multiples or fractions of base units.

Temperature Scales

Temperature is measured in Celsius (°C), Kelvin (K), and Fahrenheit (°F). The Kelvin scale is the SI unit for temperature.

• Conversion formulas:

Volume and Density

Volume is a derived unit (m3), commonly measured in liters (L) or milliliters (mL). Density is defined as mass per unit volume:

Energy Units

The SI unit of energy is the joule (J):

Another common unit is the calorie (cal):

Uncertainty in Measurement

Accuracy, Precision, and Significant Figures

All measurements have some degree of uncertainty. 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 reflect the precision of a measured quantity.

• Rules for 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

• 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

Unit Conversions

Dimensional analysis is a method for converting between units using conversion factors. A conversion factor is a ratio equal to one, used to change units without changing the value of a measurement.

• Example: To convert inches to centimeters, use .

• Set up the conversion so that units cancel appropriately.

Appendix: Common Elements and Their Symbols

Some symbols are derived from Latin names (e.g., Na from natrium for sodium).

Composition of Earth's Crust and Human Body

Only a few elements make up the majority of Earth's crust and the human body by mass. Oxygen is the most abundant element in both.