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 in general chemistry.

• Element: The simplest type of matter, composed of only one kind of atom.

• Compound: Matter composed of two or more different elements that are chemically bonded together.

• Mixture: Matter composed of elements and/or compounds that are physically mixed together, not chemically bonded.

Examples: Gold bar (element), water (compound), air (mixture).

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical:

• Physical Change: Alters the physical state or appearance without changing the composition (e.g., melting, dissolving, tearing).

• Chemical Change: Alters the chemical composition, resulting in new substances (e.g., burning, rusting, cooking).

Reversible changes (such as phase changes) can be undone, while irreversible changes (such as most chemical reactions) cannot.

Chemical and Physical Properties

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes, resulting in new substances.

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

Physical Properties

Physical properties can be observed or measured without changing the substance's chemical identity.

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

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, color, melting point, boiling point, luster.

Extensive Properties

Extensive properties depend on the amount of substance present. They are additive for independent, non-interacting subsystems.

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

Temperature and Heat

Temperature vs. Heat

Thermal energy is the sum of the kinetic and potential energies 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 Conversions

Temperature can be measured in degrees Celsius (ºC), Fahrenheit (ºF), and Kelvin (K). The following equations are used for conversions:

• $K = \text{ºC} + 273.15$

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

Scientific Notation and SI Units

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.

• Standard Notation: The usual way of writing numbers.

• Conversion: Move the decimal point to create a coefficient between 1 and 10, adjusting the exponent accordingly.

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 denote multiples or fractions of base units, making it easier to express very large or small quantities.

• Examples: kilo- (103), centi- (10-2), milli- (10-3), micro- (10-6), nano- (10-9).

Significant Figures

Rules for Significant Figures

Significant figures reflect the precision of a measured value. The more significant figures, the more precise the measurement.

• 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.

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 are ratios that relate different units and are used in dimensional analysis to convert from one unit to another.

• Example: 1 inch = 2.54 cm

• Dimensional Analysis: Multiply by conversion factors so that units cancel, leaving the desired unit.

Density

Definition and Formula

Density is the amount of mass per unit volume. It is a key property for identifying substances and solving various chemical problems.

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

Density of Geometric and Non-Geometric Objects

For regular shapes, use geometric formulas to find volume. For irregular objects, use water displacement to determine volume.

Example: If a solid displaces 60 mL of water and has a mass of 0.045 lbs, its density can be calculated in g/mL.

*Additional info: This guide covers foundational concepts in general chemistry, including matter classification, properties, measurement, and calculations essential for laboratory and theoretical work.*