Introduction to Chemistry: Matter, Properties, and Measurement

Chemistry & Matter

The Central Role of Chemistry

Chemistry is the study of matter, its properties, composition, and the changes it undergoes. It connects to many scientific fields, including biology, physics, geology, medicine, and environmental science. Chemistry helps us understand the world at the molecular and atomic levels, influencing everything from daily life to advanced technology.

• Examples in daily life: Cooking, cleaning, digestion, and even breathing involve chemical processes.

• Applications: Chemistry is foundational in fields such as pharmacology, toxicology, engineering, and environmental science.

Scientific Models

Definition and Purpose

Scientific models are tangible items, pictures, or mathematical equations used to represent invisible processes. They help visualize and understand complex chemical phenomena.

• Examples: Bohr model of the atom, the carbon cycle, and mathematical equations describing chemical reactions.

Matter: Properties and Classification

Definition of Matter

Matter is anything that has mass and occupies volume. On Earth, the terms mass and weight are often used interchangeably, though weight specifically refers to the gravitational force acting on an object's mass.

• Mass: The measure of the amount of matter in an object.

• Weight: The measure of the gravitational force on the matter in an object.

Physical Properties of Matter

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

Property	Examples
Temperature	0°C for ice water, 100°C for boiling water
Mass	A nickel weighs 5 g, a penny weighs 2.5 g
Color	Sulfur is yellow, bromine is reddish-brown
Taste	Acids are sour, bases are bitter
Odor	Benzyl acetate smells like jasmine
Boiling point	Water boils at 100°C, ethyl alcohol at 78.5°C
Hardness	Diamond is exceptionally hard
Density	1.00 g/mL for water, 19.3 g/cm³ for gold

Physical Changes

Physical changes are changes in which the chemical identity of the substance is not changed. Examples include melting, freezing, and dissolving.

Chemical Properties of Matter

Chemical properties can only be studied by forming new substances.

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)
Nitroglycerin	Explodes (decomposes to produce a mixture of gases)
Carbon monoxide	Is toxic (combines with hemoglobin, causing anoxia)
Neon	Is inert (does not react with anything)

Chemical Changes

Chemical changes are changes in which the chemical identity of the substance does change. Examples include rusting, burning, and decomposition.

• Example: A bicycle left outdoors begins to rust (iron reacts with oxygen to form iron oxide).

Classification of Matter

States of Matter

• Solid: Definite shape and volume.

• Liquid: Definite volume but no definite shape.

• Gas: Neither definite volume nor definite shape.

Elements

Elements are composed of one type of atom (same number of protons). Atoms are the smallest particles of an element. Elements are represented by chemical symbols (e.g., H for hydrogen, O for oxygen).

Compounds & Molecules

• Compounds: Made of two or more elements chemically combined in fixed ratios (e.g., NaCl, H2O, C6H12O6).

• Molecules: Groups of atoms bonded together as a unit. Includes compounds and diatomic elements (e.g., O2, N2).

Mixtures

A mixture is a physical blend of two or more substances.

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

• Heterogeneous mixtures: Not uniform in composition (e.g., soil, granite).

Types of Matter

Type	Example
Element	Gold (Au)
Compound	Water (H2O)
Homogeneous mixture	Rose gold (gold & copper)
Heterogeneous mixture	Granite (mixture of minerals)

The Measurement of Matter

SI Base Units

Physical Quantity	Name of Unit	Symbol of Unit
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

Volume: The SI base unit of volume is the cubic meter (m3).

Numerical Prefixes

Exponential Expression	Decimal Equivalent	Prefix	Symbol
109	1,000,000,000	giga	G
106	1,000,000	mega	M
103	1,000	kilo	k
10-2	0.01	centi	c
10-3	0.001	milli	m
10-6	0.000001	micro	μ
10-9	0.000000001	nano	n

Scientific Notation

• Exponential notation: Writing a number as the product of a coefficient and a power of 10.

• Scientific notation: Coefficient has a value between 1 and 10 or -1 and -10.

Examples:

• 54,700,000,000 in scientific notation: $5.47 \times 10^{10}$

• 0.00017 in scientific notation: $1.7 \times 10^{-4}$

• 18,000 in scientific notation: $1.8 \times 10^{4}$

• 4.30 × 103 in standard notation: 4,300

Density

Density is the mass of a substance per unit volume.

Formula:

$d = \frac{m}{V}$

• Example: If a gold bar has a mass of 89.4 g and a volume of 10 cm3, its density is $8.94 \text{ g/cm}^3$.

Energy

Definition and Forms

Energy is the ability to change matter, either physically or chemically. It is often described as the "ability to do work."

• Potential energy: Stored energy.

• Kinetic energy: Energy in motion.

Heat vs Temperature

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

• Temperature: The average kinetic energy of the atoms or molecules that make up an object.

Units of Heat

• Heat energy is measured in calories or joules.

• One calorie (cal) is the amount of heat required to change the temperature of 1.00 g of water by 1.00°C.

• 1 calorie = 4.184 joules (J)

$1 \text{ cal} = 4.184 \text{ J}$

Temperature Scales and Conversion

• Celsius (°C): Water freezes at 0°C and boils at 100°C.

• Kelvin (K): Absolute zero is 0 K; water freezes at 273.15 K.

• Fahrenheit (°F): Water freezes at 32°F and boils at 212°F.

Celsius to Kelvin conversion:

$K = ^\circ C + 273.15$

• Example: Room temperature is 25°C. In Kelvin: $K = 25 + 273.15 = 298.15$ K

Summary of Key Concepts

• Chemistry studies matter, its properties, and changes.

• Matter is classified by its physical and chemical properties, states, and composition (elements, compounds, mixtures).

• Measurement in chemistry uses SI units, scientific notation, and density calculations.

• Energy, heat, and temperature are fundamental to understanding physical and chemical changes.