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Introduction to Chemistry
What is Chemistry?
Chemistry is the scientific study of the properties, composition, and behavior of matter. It is a central science that connects and enhances our understanding of various fields such as biology, physics, medicine, and environmental science.
Matter is anything that has mass and occupies space.
Chemistry explores how substances interact, combine, and change to form new substances.
Applications of chemistry are found in energy, biochemistry, technology, and medicine.
Matter and Its Classification
Atoms, Elements, Compounds, and Mixtures
All matter is composed of atoms, which are the fundamental building blocks. Elements consist of only one type of atom, while compounds are made from two or more different elements chemically bonded together. Mixtures are physical combinations of two or more substances.
Element: A pure substance made of only one kind of atom.
Compound: A substance composed of two or more different elements in a fixed ratio.
Mixture: A combination of two or more substances that retain their individual properties and can be separated by physical means.
States of Matter
Matter exists in three primary states: solid, liquid, and gas. The state depends on the arrangement and movement of 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 of Matter by Composition
Matter can be classified based on its uniformity and composition into pure substances and mixtures.
Pure Substance: Has a fixed composition and distinct properties (elements and compounds).
Mixture: Composition can vary; can be homogeneous (solution) or heterogeneous.
Properties and Changes of Matter
Physical and Chemical Properties
Properties of matter are categorized as physical or chemical.
Physical Properties: Can be observed without changing the substance (e.g., boiling point, density, color).
Chemical Properties: Can only be observed when a substance is transformed into another substance (e.g., flammability, reactivity).
Intensive and Extensive Properties
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: Alters the state or appearance without changing composition (e.g., melting, boiling).
Chemical Change: Results in the formation of 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 using a porous barrier.
Distillation: Separates substances based on differences in boiling points.
Chromatography: Separates substances based on their ability to adhere to a solid surface.
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.
Physical Quantity | Name of Unit | Abbreviation |
|---|---|---|
Mass | Kilogram | kg |
Length | Meter | m |
Time | Second | s or sec |
Temperature | Kelvin | K |
Amount of substance | Mole | mol |
Electric current | Ampere | A or amp |
Luminous intensity | Candela | cd |
Metric System Prefixes
Prefixes are used to express multiples or fractions of base units for convenience.
Prefix | Abbreviation | Meaning | Example |
|---|---|---|---|
Kilo | k | 103 | 1 kilometer (km) = 103 m |
Centi | c | 10-2 | 1 centimeter (cm) = 10-2 m |
Milli | m | 10-3 | 1 milliliter (mL) = 10-3 L |
Micro | μ | 10-6 | 1 micrometer (μm) = 10-6 m |
Nano | n | 10-9 | 1 nanometer (nm) = 10-9 m |
Volume and Its Units
Volume is a derived unit, calculated from length. Common units include the liter (L) and milliliter (mL).
1 L = 1 dm3
1 mL = 1 cm3
Temperature Scales
Temperature is measured using the Celsius, Kelvin, and Fahrenheit scales. The Kelvin scale is the SI standard.
Celsius (°C): Based on water's freezing (0°C) and boiling points (100°C).
Kelvin (K): Absolute scale; 0 K is absolute zero. Conversion:
Fahrenheit (°F): Used in the U.S. for weather. Conversions:
Density
Density is a physical property defined as mass per unit volume.
Formula:
Common units: g/mL or g/cm3
Measurement and Uncertainty
Exact and Inexact Numbers
Exact numbers are defined or counted values, while inexact numbers arise from measurements and have some uncertainty.
Accuracy and 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 or calculated quantity.
All nonzero digits are significant.
Zeros between significant digits are significant.
Leading zeros are not significant.
Trailing zeros are significant if a decimal point is present.
For addition/subtraction: round to the least significant decimal place.
For multiplication/division: round to the least number of significant figures in any value used.
Dimensional Analysis
Dimensional analysis is a method for converting between units using conversion factors.
Set up conversion factors so that units cancel appropriately.
Example: To convert meters to inches, use .
Additional info: This guide covers the foundational concepts of matter, measurement, and the scientific approach to quantifying and classifying substances, which are essential for all further study in general chemistry.
