Introduction to Matter

Definitions and Properties

Matter is anything that has mass and occupies space. Understanding the basic properties and classification of matter is foundational in chemistry.

• Mass: The amount of matter in an object; measured in grams (g), kilograms (kg), etc.

• Volume: The amount of space an object occupies; common units include liters (L), cubic decimeters (dm3), milliliters (mL), and cubic centimeters (cm3).

• State of Matter: Matter exists primarily as solids, liquids, or gases, each with distinct properties.

• Composition: The types and amounts of simpler substances that make up a sample of matter (e.g., copper, water).

• Atom: The basic building block of matter, consisting of protons, neutrons, and electrons.

Classification of Matter

Elements and Compounds

Matter can be classified as either a pure substance or a mixture. Pure substances include elements and compounds.

• Element: A substance that contains only one type of atom.

• Monatomic Elements: Consist of single, unbonded atoms (e.g., noble gases like Ne, Ar).

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

• Diatomic Elements: Elements that naturally exist as molecules of two atoms (e.g., O2, N2).

• Allotropes: Different forms of the same element in the same state (e.g., O2 and O3 for oxygen; diamond and graphite for carbon).

• Compound: A substance containing two or more different types of atoms chemically bonded together. Compounds have properties different from their constituent elements (e.g., NaCl is very different from sodium or chlorine alone).

• Atoms can only be altered by nuclear means; molecules can be altered by chemical means.

Examples of Chemical Reactions:

• Dehydration of sugar: $C_{12}H_{22}O_{11}(s) \rightarrow 12C(s) + 11H_2O(g)$

• Electrolysis of water: $2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$

Mixtures

Mixtures are combinations of two or more substances that are not chemically bonded. They can be separated by physical means.

• Homogeneous Mixture (Solution): Uniform composition and properties throughout (e.g., saltwater, air).

• Heterogeneous Mixture: Non-uniform composition; different parts have different properties (e.g., salad, sand in water).

• Alloy: A homogeneous mixture of metals (e.g., brass, bronze).

• Suspension: A heterogeneous mixture where particles settle over time (e.g., muddy water).

Chart for Classifying Matter

The following chart summarizes the classification of matter:

Separating Mixtures

Mixtures can be separated by physical means, which do not involve changing the chemical identity of the substances.

1. Sorting: Physically separating based on observable properties.

2. Filtration: Separating solids from liquids using a filter.

3. Magnet: Using a magnet to separate magnetic materials.

4. Chromatography: Separating substances based on their movement through a medium.

5. Density: Separating based on differences in density.

6. Distillation: Separating based on differences in boiling points.

Density and Density Calculations

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and predicting whether an object will float or sink in a fluid.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/cm3 for solids, g/mL for liquids

• Density of water: Approximately 1.00 g/mL at room temperature

Example Calculations:

1. A sample of lead (Pb) has mass 22.7 g and volume 2.0 cm3. Density: $\frac{22.7\,g}{2.0\,cm^3} = 11.35\,g/cm^3$

2. Another sample of lead occupies 16.2 cm3. If density is known, mass can be found by $\text{Mass} = \text{Density} \times \text{Volume}$.

3. A solid cylinder with radius 1.8 cm and height 1.5 cm: Volume $= \pi r^2 h$

4. A rectangular solid with edge lengths 8.2 cm, 5.1 cm, and 4.7 cm: Volume $= l \times w \times h$

Physical and Chemical Properties

Properties of matter can be classified as physical or chemical, and 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's chemical identity (e.g., melting point, density).

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

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

Examples:

• Electrical conductivity

• Heat content (total energy)

• Ductility: Ability to be drawn into wire

• Malleability: Ability to be hammered into shape

• Brittleness

• Magnetism

States of Matter and Changes of State

Matter exists in three primary states: solid, liquid, and gas. Each state has characteristic particle arrangements and energy levels.

• 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.

Changes of state include melting, freezing, condensation, evaporation, sublimation, and deposition.

Energy and Chemical Changes

Kinetic Energy and Conservation of Energy

Kinetic energy is the energy of motion. The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed.

• Example: Combustion of acetylene $C_2H_2 + O_2 \rightarrow CO_2 + H_2O$

Endothermic and Exothermic Changes

• Endothermic: System absorbs heat (e.g., water boiling, ice melting).

• Exothermic: System releases heat (e.g., water freezing, combustion).

The Mole Concept

Atoms and molecules are counted using the mole, a fundamental unit in chemistry.

• 1 mole = $6.02 \times 10^{23}$ particles (Avogadro's number)

• The mass of 1 mole of an element (in grams) equals its atomic mass from the periodic table.

Island Diagram

The island diagram helps convert between mass, moles, and number of particles (atoms or molecules):

• Mass ↔ Moles: Use molar mass (g/mol)

• Moles ↔ Particles: Use Avogadro's number

Example Problems:

1. How many moles is $3.79 \times 10^{25}$ atoms of zinc?

2. How many atoms is 0.68 moles of zinc?

3. How many grams is 5.69 moles of uranium?

4. How many grams is $2.65 \times 10^{23}$ atoms of neon?

5. How many atoms is 421 g of promethium?

Summary Table: Classification of Matter

Additional info: Some explanations and examples have been expanded for clarity and completeness, and standard chemical terminology has been used throughout.