Matter and Energy

Introductory Definitions

This section introduces the fundamental concepts of matter and energy, which are foundational to the study of chemistry.

• Matter: Anything that has mass and occupies space.

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

• Weight: The force exerted by gravity on an object’s mass.

• Volume: The amount of space an object occupies. Units: L, dm3, mL, cm3

States of Matter

Matter exists in different physical forms known as states.

• Solid: Definite shape and volume (e.g., copper).

• Liquid: Definite volume but no definite shape (e.g., water).

• Gas: No definite shape or volume.

Atoms and Elements

Atoms are the basic building blocks of matter. Elements are pure substances consisting of only one type of atom.

• Atom: The smallest unit of an element that retains its chemical properties.

• Element: A substance made up of only one kind of atom.

• Monatomic elements: Elements that exist as single atoms (e.g., noble gases).

• Polyatomic elements: Elements that consist of several like atoms bonded together (e.g., O2, P4).

• Allotropes: Different forms of the same element in the same state of matter (e.g., oxygen O2 and ozone O3).

• Molecule: A neutral group of bonded atoms.

Classification Table: Atoms and Molecules

This table compares different atomic and molecular forms.

Compounds

Compounds are substances that contain two or more different types of atoms chemically bonded together.

• Compound: A substance composed of two or more elements in fixed proportions.

• Properties of compounds differ from those of their constituent elements.

• Atoms in compounds can only be separated by chemical means; molecules can be altered by chemical means.

• Example: Sodium chloride (NaCl) is a compound of sodium and chlorine.

Sample Chemical Equations:

• Dehydration of sugar:

• Electrolysis of water:

Compound Composition

All samples of a given compound have the same composition by mass.

• Law of Definite Proportions: A chemical compound always contains exactly the same proportion of elements by mass.

• Example Problem: Phosgene gas (COCl2) is 12.1% carbon, 15.2% oxygen, and 71.7% chlorine by mass. Find the mass of each element in 254 g of COCl2.

Classifying Matter

Matter can be classified as pure substances or mixtures.

• Pure Substances: Elements and compounds with uniform composition.

• Mixtures: Combinations of two or more substances not chemically bonded.

Types of Mixtures

• Homogeneous Mixture (Solution): Uniform composition throughout (e.g., air, 24K gold).

• Heterogeneous Mixture: Non-uniform composition; properties vary within the sample (e.g., suspensions, 14K gold).

Classification Chart

Separating Mixtures

Mixtures can be separated by physical means or physical changes.

• Sorting

• Filtration

• Magnetism

• Chromatography

• Density

• Distillation

Density

Density describes how tightly packed the particles are in a substance.

• Density Formula:

• Typical units: g/cm3 for solids, g/mL for fluids.

• The density of a liquid or solid is nearly constant, regardless of sample size.

Example Calculation: A sample of lead (Pb) has mass 22.7 g and volume 2.0 cm3. Find sample’s density.

Properties of Matter

Matter has chemical and physical properties, which can be classified as extensive or intensive.

• Chemical Properties: Describe how a substance reacts with other substances (e.g., reactivity with water).

• Physical Properties: Can be observed without changing the substance (e.g., electrical conductivity, color).

• Extensive Properties: Depend on the amount of substance present (e.g., mass, volume).

• Intensive Properties: Do not depend on the amount of substance (e.g., density, melting point).

States of Matter and Changes in State

Matter can change between solid, liquid, and gas states through physical processes.

• Solid: Particles are closely packed in a fixed arrangement.

• Liquid: Particles are close but can move past each other.

• Gas: Particles are far apart and move freely.

• Phase Changes: Melting, freezing, vaporization, condensation, sublimation, deposition.

Energy

Energy is the ability to do work. It exists in different forms and is conserved in chemical processes.

• Potential Energy: Stored energy due to position or composition.

• Kinetic Energy: Energy of motion.

• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

Example: For the combustion of acetylene:

Energy Changes

• Endothermic Change: System absorbs heat (e.g., water boiling, paper burning).

• Exothermic Change: System releases heat (e.g., water freezing, ice melting).

The Mole

The mole is a counting unit used to express amounts of a chemical substance.

• 1 mole = atoms (Avogadro’s number).

• For any element, 1 mole has a mass in grams equal to its atomic mass from the periodic table.

Island Diagram: Mass, Moles, and Particles

This diagram shows the relationships between mass, moles, and number of particles.

• 1 mol = molar mass (in g)

• 1 mol = atoms

Sample Problems

• How many moles in atoms of zinc?

• How many atoms in 0.66 moles of zinc?

• How many grams in 5.69 moles of uranium?

• How many atoms in atoms of neon?

• How many atoms in 421 g of promethium?

Additional info: Some diagrams and tables were inferred and expanded for clarity. All equations are provided in LaTeX format for academic completeness.