Introduction to General Chemistry: Matter, Properties, and Measurement

Introduction to General Chemistry

Matter and Its Classification

Chemistry is the scientific study of matter, its properties, and the changes it undergoes. Matter is anything that occupies space and has mass. It can be classified based on its physical state and composition.

• Physical State: Solid, liquid, or gas

• Composition: Elements, compounds, or mixtures

Type	Definition/Example	Symbol
Element	Pure substance made of a single type of atom	H, O, Na
Compound	Pure substance made of two or more elements chemically combined	H2O, CO2
Mixture	Physical combination of substances	Air, saltwater

Physical and Chemical Changes

Physical Changes

Physical changes alter the appearance or state of a substance without changing its composition.

• Examples: Melting, freezing, boiling, dissolving

Chemical Changes

Chemical changes (chemical reactions) result in the formation of new substances with different properties.

• Examples: Rusting of iron, burning of wood

Phase Changes: Reversible and Irreversible

Reversible Changes

Reversible changes can be undone, such as phase changes between solid, liquid, and gas (melting, freezing, boiling).

Irreversible Changes

Irreversible changes cannot be undone by simple physical means (e.g., burning, digestion).

Phase Change	Social Meaning	Good Example
Melting	Solid to liquid	Ice melting
Boiling	Liquid to gas	Water boiling
Freezing	Liquid to solid	Water freezing

Chemical and Physical Properties

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes or reactions.

• Examples: Flammability, reactivity with acid

Physical Properties

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

• Examples: Color, density, melting point, boiling point

Intensive vs. Extensive Properties

Intensive Properties

Intensive properties do not depend on the amount of substance present.

• Examples: Density, boiling point, color

Extensive Properties

Extensive properties depend on the amount of substance present.

• Examples: Mass, volume, length

Property Type	Examples
Intensive	Density, melting point, color
Extensive	Mass, volume, length

SI Units and Measurements

SI Base Units

The International System of Units (SI) is the standard system used in chemistry for physical measurements.

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

Derived Units, Area, and Volume

• Area: $\text{Area} = \text{length} \times \text{width}$

• Volume: $\text{Volume} = \text{length}^3$

Metric Prefixes

Metric Prefix Multipliers

Metric prefixes are used to indicate multiples or fractions of SI units.

Prefix	Symbol	Multiplier
kilo	k	$10^3$
centi	c	$10^{-2}$
milli	m	$10^{-3}$
micro	\mu	$10^{-6}$
nano	n	$10^{-9}$

Temperature and Scientific Notation

Temperature Scales

Temperature can be measured in Celsius, Kelvin, or Fahrenheit. The Kelvin scale is the SI unit for temperature.

Scale	Conversion Formula
Celsius to Kelvin	$K = ^\circ C + 273.15$
Celsius to Fahrenheit	$^\circ F = (9/5) ^\circ C + 32$

Scientific Notation

Scientific notation expresses numbers as a coefficient times a power of ten (e.g., $3.0 \times 10^4$).

Significant Figures

Rules for Significant Figures

• Nonzero numbers are always significant

• Zeros between nonzero digits are significant

• Leading zeros are not significant

• Trailing zeros are significant only if there is a decimal point

Significant Figures in Calculations

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places

Conversion Factors and Dimensional Analysis

Conversion Factors

Conversion factors are ratios used to express measurements in different units.

Unit	Equivalent	Factor
1 km	1000 m	1 km / 1000 m
1 m	100 cm	1 m / 100 cm

• Dimensional analysis is a method for converting units using conversion factors.

Density and Measurement

Density

Density is the ratio of mass to volume.

• Formula: $\text{Density} = \frac{\text{mass}}{\text{volume}}$

Density of Common Objects

• Objects with density less than water float; those with greater density sink.

Density in Water Displacement

Density can be measured by water displacement: the volume of water displaced equals the volume of the object.

• Example: If a metal object displaces 10 mL of water and has a mass of 78 g, its density is $7.8 \text{ g/mL}$.