Matter and Energy: States, Classification, and Properties

Matter and Its States

Definition of Matter

Matter is any substance that has mass and occupies volume. All physical objects are composed of matter, which exists in one of three primary physical states: solid, liquid, or gas.

• Solid: Definite shape and volume; particles are tightly packed.

• Liquid: Indefinite shape (takes the shape of its container) but definite volume; particles are less tightly packed and can move past one another.

• Gas: Indefinite shape and volume; particles are far apart and move freely.

Kinetic-Molecular Theory

The Kinetic-Molecular Theory explains the states of matter in terms of the motion and energy of particles:

• Solids: Particles vibrate in place and have the least energy.

• Liquids: Particles move more freely than in solids and have intermediate energy.

• Gases: Particles move rapidly and have the most energy.

Physical States of Matter: Comparison Table

Property	Solid	Liquid	Gas
Shape	Fixed	Variable	Variable
Volume	Fixed	Fixed	Variable
Compressibility	Not significant	Not significant	Significant

Changes in Physical States

Phase Changes

Substances can transition between solid, liquid, and gas states through physical processes:

• Melting: Solid to liquid (energy absorbed)

• Freezing: Liquid to solid (energy released)

• Vaporizing (Boiling/Evaporation): Liquid to gas (energy absorbed)

• Condensing: Gas to liquid (energy released)

• Sublimation: Solid to gas (energy absorbed)

• Deposition: Gas to solid (energy released)

Example: Water exists as ice below 0°C, as liquid between 0°C and 100°C, and as vapor above 100°C.

Classification of Matter

Mixtures vs. Pure Substances

Matter can be classified as either mixtures or pure substances:

• Mixtures: Physical blends of two or more substances; can be separated physically.

• Pure Substances: Composed of only one type of substance; cannot be separated physically.

Types of Mixtures

• Heterogeneous Mixtures: Non-uniform composition (e.g., sand and water).

• Homogeneous Mixtures (Solutions): Uniform composition throughout (e.g., saltwater).

Types of Pure Substances

• Compounds: Can be chemically separated into elements (e.g., water into hydrogen and oxygen).

• Elements: Cannot be broken down further by chemical reactions; listed in the periodic table.

Occurrence and Properties of Elements

Abundance of Elements

There are over 100 naturally occurring elements, with only 10 accounting for more than 95% of the mass of Earth's crust, water, and atmosphere.

Element	Mass Percent
Oxygen	49.5%
Silicon	25.7%
Aluminum	0.5%
Iron	4.7%
Calcium	3.4%
Sodium	2.6%
Potassium	2.4%
Magnesium	1.9%
Hydrogen	0.9%
Titanium	0.6%

Example: Oxygen is the most common element in both Earth's crust and the human body.

Element Names and Symbols

• Each element has a unique name and a one- or two-letter symbol (e.g., H for hydrogen, Na for sodium).

• Symbols may derive from Latin names (e.g., Au for gold, Ag for silver).

• Many metals have names ending in -ium (e.g., magnesium, titanium).

Types of Elements

• Metals: Solids (except mercury), high melting points, high densities, metallic luster, good conductors, ductile, and malleable.

• Nonmetals: Low melting points, low densities, dull appearance, poor conductors, brittle.

• Semimetals (Metalloids): Exhibit properties of both metals and nonmetals (e.g., silicon is a semiconductor).

Summary Table: Metals vs. Nonmetals

Property	Metals	Nonmetals
Physical State	Solid	Solid, gas
Appearance	Metallic luster	Dull
Pliability	Malleable, ductile	Brittle
Conductivity	Heat, electricity	Nonconductor
Density	Usually high	Usually low
Melting Point	Usually high	Usually low
Chemical Reactivity	React with nonmetals	React with metals and nonmetals

Periodic Table of the Elements

Structure and Organization

The periodic table arranges elements by increasing atomic number. Metals are on the left, nonmetals on the right, and semimetals/metalloids are between.

• Each element is assigned an atomic number (number of protons).

• Physical states of elements at 25°C are indicated (solid, liquid, gas).

Elements Beyond 104

Heavier elements beyond the current periodic table are discovered and named by IUPAC, often using Latin prefixes and the suffix -ium until official names are assigned.

Law of Definite Composition (Law of Constant Composition)

The law of definite composition states that compounds always contain the same elements in a constant proportion by mass, regardless of the source or method of preparation.

• For example, water (H2O) always contains hydrogen and oxygen in a mass ratio of approximately 1:8.

Chemical Formulas

Definition and Writing

A chemical formula expresses the number and type of atoms in a molecule. Subscripts indicate the number of each atom; if only one atom is present, no subscript is used.

• Example: The formula for sulfuric acid is $H_2SO_4$.

• Example: A molecule of vitamin B6 with 6 carbon, 6 hydrogen, 2 nitrogen, and 1 oxygen atom is written as $C_6H_6N_2O$.

Physical and Chemical Properties and Changes

Physical Properties

Characteristics that can be observed without changing the substance's composition (e.g., appearance, melting/boiling point, density, conductivity).

Chemical Properties

Describe how a substance reacts with other substances (e.g., flammability, reactivity).

Physical vs. Chemical Change

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

• Chemical Change: Alters chemical composition; involves chemical reactions (e.g., burning, rusting).