Introduction to Chemistry: Foundations and Measurement

Chemistry: The Chemical World

Introduction to Chemistry

Chemistry is the study of matter and its changes. It is a central science that connects and underpins many other scientific disciplines, including biology, physics, medicine, and engineering. Everything we do involves chemistry, from cooking food to reading labels on organic vegetables.

• Matter: Anything that has mass and occupies space (volume).

• Chemistry: The science that investigates the properties, composition, and changes of matter.

Science and Technology

Nature of Science

Science is the process of seeking an understanding of the underlying principles of nature. It involves two main facets:

• Technological (factual): Practical applications and facts.

• Philosophical (theoretical): Theories and speculation about nature.

Technology is the direct application of scientific knowledge to solve problems. Chemistry, as a discipline, deals with the behavior of matter.

Green and Sustainable Chemistry

Environmental Chemistry

• Green Chemistry: Uses materials and processes designed to prevent or reduce pollution at its source.

• Sustainable Chemistry: Meets the needs of the present generation without compromising the needs of future generations.

Characteristics of Science

Scientific Method and Reasoning

• Testable: Can be tested by experiments or observation.

• Reproducible: Results can be repeated by others.

• Explanatory: Provides explanations for phenomena.

• Predictive: Can predict future events or results.

• Tentative: Open to change as new evidence emerges.

Scientific Hypotheses, Laws, and Theories

• Hypothesis: A testable explanation of observed data, tested by experiments.

• Scientific Law: Summarizes large amounts of scientific data and describes natural phenomena, often mathematically (e.g., Boyle's Law: $PV = k$).

• Scientific Theory: A set of tested hypotheses that explain natural phenomena. Theories are the best current explanations but are always tentative.

• Scientific Models: Tangible items or pictures used to represent invisible processes (e.g., molecular models).

Matter and Its Properties

Physical and Chemical Properties

• Physical Properties: Can be observed without changing the substance (e.g., color, mass, weight, boiling point, density).

• Chemical Properties: Can only be observed by forming new substances (e.g., iron rusting, carbon burning).

Property	Example
Temperature	0°C for ice water, 100°C for boiling water
Mass	A nickel weighs 5 g
Color	Sulfur is yellow
Boiling point	Water boils at 100°C
Density	1.00 g/mL for water

Additional info: Table includes more properties such as taste, odor, and hardness.

Substance	Typical Chemical Property
Iron	Rusts (combines with oxygen to form iron oxide)
Carbon	Burns (combines with oxygen to form carbon dioxide)
Silver	Tarnishes (combines with sulfur to form silver sulfide)
Neon	Inert (does not react with anything)

Physical and Chemical Changes

• Physical Change: The chemical identity of the substance is not changed (e.g., melting, freezing, sanding wood).

• Chemical Change: The substance is transformed into a new substance (e.g., milk turning to cheese, sodium chloride breaking down into sodium and chlorine gas).

Classification of Matter

States of Matter

• Solid: Definite shape and volume.

• Liquid: Definite volume, no definite shape.

• Gas: Neither definite volume nor shape.

Elements, Compounds, and Mixtures

• Element: Composed of one type of atom, represented by chemical symbols (e.g., Cl, H, Mg).

• Compound: Made of two or more elements chemically combined (e.g., NaCl, H2O, C6H12O6).

• Molecule: A group of atoms bonded together, representing the smallest unit of a compound.

• Mixture: A physical blend of two or more substances.

• Homogeneous Mixture: Uniform in composition (e.g., saltwater).

• Heterogeneous Mixture: Not uniform in composition (e.g., salad).

Measurement and Problem Solving

SI Units and Prefixes

Measurement in chemistry uses the International System of Units (SI). The seven base units are:

Physical Quantity	Name of Unit	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

Common prefixes include kilo- (103), centi- (10-2), milli- (10-3), and micro- (10-6).

Density

Density is a fundamental property defined as the amount of matter in a given amount of space.

• Formula: $d = \frac{m}{V}$

• Units: g/cm3 or kg/m3

• Example: The density of copper is 8.94 g/cm3.

Practice Problem: Calculate the density of a metal sample with a mass of 18.96 g and a volume of 4.31 cm3:

$d = \frac{18.96\ g}{4.31\ cm^3} = 4.40\ g/cm^3$

Energy: Heat and Temperature

Forms of Energy

• Potential Energy: Stored energy.

• Kinetic Energy: Energy of motion.

Heat vs Temperature

• Heat: Energy transferred from hotter objects to cooler objects.

• Temperature: The average kinetic energy of the atoms or molecules in a substance.

Units of Heat

• Calorie (cal): The amount of heat required to raise the temperature of 1.00 g of water by 1.00°C.

• Joule (J): The SI unit of energy. $1\ cal = 4.184\ J$

• Food Calorie (Cal): 1 Cal = 1 kilocalorie = 1000 cal = 4184 J

Temperature Scales and Conversions

• Celsius (°C) and Kelvin (K) are commonly used in chemistry.

• Conversion: $K = ^\circ C + 273.15$

• Example: Diethyl ether boils at 36°C. Its boiling point in Kelvin is $36 + 273.15 = 309.15\ K$.