Introduction to Matter

Definitions and Properties

Matter is anything that has mass and occupies volume. Understanding the basic properties and classification of matter is foundational in general 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: liters (L), cubic decimeters (dm3), milliliters (mL), cubic centimeters (cm3).

• State of Matter: The physical form in which matter exists: solid, liquid, or gas.

• Composition: The types of particles (atoms, molecules) that make up a substance. Example: Copper (element), Water (compound).

• Properties: Characteristics used to describe matter, such as color, density, melting point, etc.

• Atom: The basic building block of matter.

Classification of Matter

Elements

Elements are pure substances that contain only one type of atom.

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

• Polyatomic Elements: Consist of several like atoms bonded together.

  • Diatomic Elements: Molecules made of two atoms (e.g., O2, N2).

  • Other Polyatomic Elements: Molecules with more than two atoms (e.g., P4).

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

Compounds

Compounds are pure substances that contain two or more different types of atoms chemically bonded together. Their properties are different from those of their constituent elements.

• Examples: Na (sodium), Cl2 (chlorine) are elements; NaCl (sodium chloride) is a compound.

• Atoms can only be altered by nuclear means. Molecules can be altered by chemical means.

Example Reactions:

• Dehydration of sugar:

• Electrolysis of water:

Mixtures

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

• Homogeneous Mixtures (Solutions): Uniform composition and properties throughout (e.g., salt water, air).

• Heterogeneous Mixtures: 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 that settles over time (e.g., muddy water).

Contrast: 24K gold (pure), 14K gold (mixture/alloy).

Classification Chart

Key point: Pure substances have fixed composition; mixtures can vary in composition.

Chart for Classifying Matter

• MATTER

  • PURE SUBSTANCE

    • ELEMENT

    • COMPOUND

  • MIXTURE

    • HOMOGENEOUS

    • HETEROGENEOUS

Separation of Mixtures

Mixtures can be separated by physical means, which involve physical changes rather than chemical changes.

1. Sorting: Separating substances based on physical characteristics (e.g., color, size).

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

3. Magnet: Using a magnet to separate magnetic materials from non-magnetic ones.

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

5. Density: Separating substances based on differences in density.

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

Density and Density Calculations

Density is a physical property defined as mass per unit volume. It is nearly constant for a given substance at a specific temperature and pressure.

• Formula:

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

• Density of water: (at 4°C)

Example Calculations:

1. A sample of lead (Pb) has mass 22.7 g and volume 2.0 cm3. Find the density.

2. Another sample of lead occupies 16.2 cm3 of space. Find the mass if density is 11.35 g/cm3.

3. A solid cylinder has radius 1.8 cm, height 1.5 cm. Find its volume and density if mass is 119.5 g.

4. A rectangular solid has edge lengths 8.2 cm, 5.1 cm, and 4.7 cm. Find its volume.

Will an object sink in water? If its density is greater than 1.00 g/cm3, it will sink; if less, it will float.

Physical and Chemical Properties

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

• Physical Properties: Can be observed without changing the chemical identity (e.g., color, 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, ductility (can be drawn into wire), malleability (can be hammered into shape), brittleness, magnetism.

States of Matter and Changes of State

• Solid: Definite shape and volume; particles are closely packed in a fixed arrangement.

• Liquid: Definite volume but no definite shape; particles are close but can move past each other.

• Gas: No definite shape or volume; particles are far apart and move freely.

Changes of State: Melting, freezing, vaporization, condensation, sublimation, deposition.

Energy in Chemistry

Kinetic Energy and Conservation of Energy

• Kinetic Energy: The energy of motion.

• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed from one form to another.

Example: Combustion of acetylene:

Energy Changes

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

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

Energy Diagrams: Endothermic reactions have products at higher energy than reactants; exothermic reactions have products at lower energy than reactants.

The Mole and Counting Atoms

Atoms and molecules are extremely small, so chemists use the mole to count them in practical quantities.

• 1 mole (mol): particles (Avogadro's number).

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

Island Diagram

• Relates mass, moles, and number of particles (atoms/molecules).

• 1 mol = atoms or molecules.

Sample Problems

1. How many moles is atoms of zinc?

2. How many atoms is 0.68 moles of zinc?

3. How many grams is 5.69 moles of uranium? (U atomic mass ≈ 238 g/mol)

4. How many grams is atoms of neon? (Ne atomic mass ≈ 20.18 g/mol)

5. How many atoms is 421 g of promethium? (Pm atomic mass ≈ 145 g/mol)

Additional info: Some values (e.g., atomic masses) are standard and inferred for calculation examples.