Introduction to General Chemistry: Classification, Properties, and Measurement of Matter

Classification of Matter

Types of Matter

Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. It can be classified into three main types:

• Element: The simplest type of matter, composed of one kind of atom. Examples include gold (Au) and oxygen (O2).

• Compound: Matter composed of two or more different elements that are chemically bonded together. For example, water (H2O) and carbon dioxide (CO2).

• Mixture: Matter composed of elements and/or compounds that are physically mixed together but not chemically bonded. Mixtures can be homogeneous (uniform composition, e.g., saltwater) or heterogeneous (non-uniform composition, e.g., salad).

Example: Classify the following:

• Gatorade – Homogeneous mixture

• Crystalline sugar – Pure substance (compound)

• Lead wire – Pure substance (element)

• Salsa – Heterogeneous mixture

Physical and Chemical Changes

Physical Changes

Physical changes alter the state or appearance of matter without changing its composition. Examples include melting, freezing, dissolving, and tearing.

• Example: Dissolving sugar in water is a physical change.

Chemical Changes

Chemical changes result in the formation of new substances with different chemical properties. This involves making or breaking chemical bonds.

• Example: Iron rusting or wood burning are chemical changes.

Reversible vs. Irreversible Changes

• Reversible Change: Can be undone (e.g., melting and re-solidifying chocolate).

• Irreversible Change: Cannot be undone (e.g., baking a cake).

Chemical and Physical Properties

Chemical Properties

Chemical properties describe how a substance reacts with other substances, resulting in a change in composition.

• Examples: Flammability, reactivity with acids, toxicity, radioactivity.

Physical Properties

Physical properties can be observed or measured without changing the substance’s chemical identity. Examples include color, mass, density, melting point, and state of matter.

• Examples: Color, mass, volume, density, melting point, boiling point.

Intensive vs. Extensive Properties

Intensive Properties

Intensive properties do not depend on the amount of substance present. They are useful for identifying substances.

• Examples: Density, melting point, boiling point, color, luster.

Extensive Properties

Extensive properties depend on the amount of substance present.

• Examples: Mass, volume, length, total charge.

Temperature and Heat

Thermal Energy, Temperature, and Heat

Thermal energy is the total kinetic and potential energy of all atoms in an object. Temperature is the average kinetic energy of particles, while heat is the transfer of thermal energy from a hotter object to a cooler one.

• Temperature units: Celsius (ºC), Fahrenheit (ºF), Kelvin (K)

Temperature Conversions

• $K = \text{ºC} + 273.15$

• $\text{ºF} = 1.8 \times \text{ºC} + 32$

Scientific Notation

Format and Use

Scientific notation expresses very large or small numbers in the form $a \times 10^n$, where $1 \leq a < 10$ and $n$ is an integer.

• Coefficient: The number $a$

• Base: Always 10

• Exponent: Indicates how many places the decimal is moved

Example: $6.88 \times 10^{-12}$

SI Units and Metric Prefixes

SI Base Units

The International System of Units (SI) is based on seven base units:

Physical Quantity	Name	Symbol
Mass	kilogram	kg
Length	meter	m
Time	second	s
Temperature	kelvin	K
Amount of substance	mole	mol
Electric current	ampere	A
Luminous intensity	candela	cd

Metric Prefixes

Metric prefixes are used to express multiples or fractions of base units. For example, kilo- (k) means 103, milli- (m) means 10-3.

• Examples: 1 kilometer (km) = 1000 meters (m), 1 milligram (mg) = 0.001 grams (g)

Significant Figures

Rules for Counting Significant Figures

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a decimal number are significant.

• Exact numbers have an infinite number of significant figures.

Example: 0.003840 has 4 significant figures.

Significant Figures in Calculations

• Multiplication/Division: The result should have as many significant figures as the value with the fewest significant figures.

• Addition/Subtraction: The result should have as many decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion Factors

A conversion factor is a ratio that expresses how many of one unit are equal to another unit. For example, 1 inch = 2.54 cm.

Dimensional Analysis

Dimensional analysis is a systematic approach to problem-solving that uses conversion factors to move from one unit to another.

• Set up the problem so that units cancel appropriately, leaving only the desired unit.

Density

Definition and Formula

Density is the amount of mass per unit volume. It is a physical property that can be used to identify substances.

• For solids and liquids: units are g/cm3 or kg/L

• For gases: units are g/L

Formula:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Density of Geometric and Non-Geometric Objects

For geometric objects, use volume formulas (e.g., for a cube: $V = a^3$). For irregular objects, use water displacement to find volume.

Summary Table: Classification of Properties

Property Type	Examples
Physical Property	Color, mass, volume, density, melting point
Chemical Property	Flammability, reactivity, toxicity, radioactivity
Intensive Property	Density, color, melting point
Extensive Property	Mass, volume, length