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

Intro to General Chemistry

Classification of Matter

Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. Understanding the classification of matter is foundational to all chemical studies.

• 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, such as water (H2O).

• Mixture: Matter composed of elements and/or compounds that are physically mixed together, such as air or salad.

Pure substances include elements and compounds, while mixtures can be homogeneous (uniform composition, e.g., saltwater) or heterogeneous (non-uniform, e.g., salad).

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical:

• Physical Change: Alters the physical state without changing the chemical composition (e.g., melting, boiling, dissolving).

• Chemical Change: Alters the chemical composition, forming new substances (e.g., burning, rusting, digestion).

Physical changes are often reversible (e.g., freezing and melting), while chemical changes are usually irreversible (e.g., baking a cake).

Chemical Properties

Chemical properties describe how a substance interacts with other substances, resulting in a change in composition. These properties are observed during chemical reactions.

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

Physical Properties

Physical properties are measurable characteristics that describe the state of a substance without changing its chemical structure. They can be observed with the senses or measured directly.

• Examples: Color, mass, density, melting point, boiling point, hardness, and luster.

Intensive vs. Extensive Properties

Properties of matter can be classified as intensive or extensive:

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

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

Temperature and Heat

Temperature is a measure of the average kinetic energy of particles in a substance, while heat is the transfer of thermal energy from a hotter object to a cooler one. Temperature is measured in degrees Celsius (ºC), Fahrenheit (ºF), or Kelvin (K).

• Temperature Conversion Formulas:

• $K = \text{ºC} + 273.15$

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

Scientific Notation

Scientific notation is used to express very large or very small numbers in a compact form: $a \times 10^n$, where $1 \leq a < 10$ and $n$ is an integer.

• Positive exponent: Move the decimal to the right (number gets larger).

• Negative exponent: Move the decimal to the left (number gets smaller).

SI Units and Metric Prefixes

The International System of Units (SI) is the standard for scientific measurements. There are 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 indicate multiples or fractions of base units (e.g., kilo-, centi-, milli-).

Significant Figures

Significant figures reflect the precision of a measured value. The rules for counting significant figures are:

• 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.

Conversion Factors and Dimensional Analysis

Conversion factors are ratios that relate different units. Dimensional analysis is a systematic approach to converting between units using these factors.

• Example: To convert inches to centimeters, use the factor $1 \text{ inch} = 2.54 \text{ cm}$.

Density

Density is the amount of mass per unit volume. It is calculated as:

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

Units for solids and liquids are typically g/cm3 or kg/L; for gases, g/L.

Density of Geometric and Non-Geometric Objects

For geometric objects, volume can be calculated using formulas (e.g., for a cube: $V = a^3$). For irregular objects, volume is often determined by water displacement.

• Water Displacement: The volume of water displaced equals the volume of the object submerged.