Introduction to Chemistry: Matter, Properties, Energy, and Measurement

Chemistry: An Introduction

Definition and Scope

Chemistry is the scientific study of matter, its properties, the changes it undergoes, and the energy associated with these changes. It encompasses everything that has mass and occupies space, and seeks to understand the composition, structure, and properties of substances.

• Matter: Anything that has mass and volume (e.g., books, planets, trees, air).

• Composition: The types and amounts of simpler substances that make up a sample of matter.

• Properties: The characteristics that give each substance a unique identity.

The States of Matter

Classification of Matter by Physical State

Matter exists in three primary physical states, each with distinct characteristics:

• Solid: Fixed shape and volume; may be hard or soft, rigid or flexible.

• Liquid: Varying shape (conforms to the shape of its container) but fixed volume; has an upper surface.

• Gas: No fixed shape or volume; does not have a surface.

Physical vs. Chemical Properties

Understanding Properties of Substances

• Physical Properties: Characteristics a substance shows by itself without interacting with another substance (e.g., color, melting point, boiling point, density).

• Chemical Properties: Characteristics a substance shows when it interacts with, or transforms into, other substances (e.g., flammability, corrosiveness, reactivity).

Example: Shredding paper is a physical change (the substance remains paper), while burning paper is a chemical change (the substance becomes ash and gases).

Distinction Between Physical and Chemical Change

Types of Changes in Matter

• Physical Change: Alters the physical form, not the composition (e.g., melting ice, dissolving sugar in water).

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

Example: Water freezing or boiling is a physical change; hydrogen and oxygen reacting to form water is a chemical change.

Temperature and Change of State

Physical Changes and Reversibility

• A change of state (e.g., solid to liquid) is a physical change.

• Physical changes are often reversible by changing temperature (e.g., freezing and melting water).

• Chemical changes are generally not reversible by simple physical means (e.g., you cannot un-bake a cake).

Characteristic Properties of Copper

Comparison of Physical and Chemical Properties

Physical Properties	Chemical Properties
Easily hammered into sheets (malleable)	Slowly forms green surface coating (patina) when exposed to air
Can be stretched into wires (ductile)	Reacts with acids to release hydrogen gas
Density: 8.96 g/cm3; Melting point: 1085°C; Boiling point: 2562°C	Slowly forms deep blue solution in aqueous ammonia

Sample Problems: Identifying Changes

Practice in Distinguishing Physical and Chemical Changes

• Frost forms as the temperature drops: Physical change (phase change of water vapor to ice).

• Cornstalk grows from a seed: Chemical change (complex biochemical reactions form new substances).

• Match ignites to form ash and gases: Chemical change (combustion produces new substances).

• Perspiration evaporates: Physical change (liquid water to vapor).

• Silver tarnishes: Chemical change (reaction with sulfur compounds in air forms silver sulfide).

Energy in Chemistry

Types and Roles of Energy

• Energy: The ability to do work.

• Potential Energy: Energy due to the position of an object.

• Kinetic Energy: Energy due to the movement of an object.

Example: A ball held at a height has potential energy; when dropped, it gains kinetic energy as it falls.

Energy Changes

Stability and Conservation of Energy

• Lower energy states are more stable and favored over higher energy states.

• Law of Conservation of Energy: Energy can neither be created nor destroyed; it can only be converted from one form to another.

Equation:

$\text{Total Energy}_{\text{initial}} = \text{Total Energy}_{\text{final}}$

Potential Energy is Converted to Kinetic Energy

Examples of Energy Transformation

• In a gravitational system, potential energy is gained when a weight is lifted and converted to kinetic energy when it falls.

• In a system of two balls attached by a string, stretching the string increases potential energy, which is converted to kinetic energy when released.

• In a system of oppositely charged particles, separating the charges increases potential energy, which is converted to kinetic energy as they attract each other.

• Energy is conserved when it is transformed.

The Scientific Approach: Developing a Method

Steps of the Scientific Method

• Observations: Gathering data about natural phenomena.

• Hypothesis: A tentative explanation that can be tested by experiments.

• Experiment: Testing the hypothesis under controlled conditions.

• Model (Theory): A set of conceptual assumptions that explains data from accumulated experiments.

• Further Experimentation: Used to refine models and theories.

SI Base Units

Fundamental Units in the International System

Physical Quantity	Unit Name	Unit Abbreviation
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

Common Decimal Prefixes Used with SI Units

Multiples and Submultiples of SI Units

Prefix	Symbol	Standard Notation	Scientific Notation	Example Naming
tera	T	1,000,000,000,000	1 \times 10^{12}	teragram (Tg)
giga	G	1,000,000,000	1 \times 10^{9}	gigameter (Gm)
mega	M	1,000,000	1 \times 10^{6}	megagram (Mg)
kilo	k	1,000	1 \times 10^{3}	kilogram (kg)
deci	d	0.1	1 \times 10^{-1}	decimeter (dm)
centi	c	0.01	1 \times 10^{-2}	centimeter (cm)
milli	m	0.001	1 \times 10^{-3}	millimeter (mm)
micro	\mu	0.000001	1 \times 10^{-6}	micrometer (\mu m)
nano	n	0.000000001	1 \times 10^{-9}	nanometer (nm)
pico	p	0.000000000001	1 \times 10^{-12}	picometer (pm)
femto	f	0.000000000000001	1 \times 10^{-15}	femtometer (fm)

Volumetric Relationships in SI

Volume Units and Conversions

• The SI unit of volume is the cubic meter (m3).

• Common laboratory volumes are measured in liters (L) and milliliters (mL).

• 1 L = 1 dm3 = 1,000 mL = 1,000 cm3

Example: A cube with sides of 10 cm has a volume of 1,000 cm3 = 1 L.