Introduction to Matter

Definitions and Basic Concepts

Matter is anything that has mass and occupies space. Understanding matter and its properties is fundamental to the study of 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: The physical form in which matter exists: solid, liquid, or gas.

• Composition: The types of particles (atoms, molecules) that make up a substance. For example, copper (Cu) is an element, water (H2O) is a compound.

• Atom: The basic building block of matter.

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 unbonded, "like" atoms (e.g., He, Ne).

  • Polyatomic elements: Consist of several "like" atoms bonded together (e.g., O2, S8).

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

  • 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).

• Compound: A substance that contains 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 and chlorine).

Table: Examples of Elements and Molecules

Mixtures

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

• Homogeneous mixture (solution): Has uniform composition and properties throughout (e.g., salt water, air).

• Heterogeneous mixture: Has different composition and properties in different parts of the sample (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

Properties of Matter

Chemical and Physical 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 of the substance (e.g., color, melting point, density).

Extensive and Intensive Properties

• 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, boiling point).

Examples of Properties

• Electrical conductivity

• Reactivity with water

• Heat content (total energy)

• Ductility: Ability to be drawn into wire

• Malleability: Ability to be hammered into shape

• Brittleness: Tendency to break or shatter

• Magnetism

States of Matter and Changes of State

States of Matter

• 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: Solid to liquid

• Freezing: Liquid to solid

• Vaporization (boiling/evaporation): Liquid to gas

• Condensation: Gas to liquid

• Sublimation: Solid to gas

• Deposition: Gas to solid

Separation of Mixtures

Physical Methods

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

1. Sorting: Separating 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.

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

Definition and Calculation

Density is the mass per unit volume of a substance. It is an intensive property and is nearly constant for a given substance under standard conditions.

• Formula:

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

• To find volume, use:

  • For regular solids:

  • For cylinders:

• Density of water: 1.00 g/mL (at 4°C)

Example Problems

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

• Another sample of lead occupies 16.2 cm3. Find the mass if density is known.

• A solid cylinder with radius 1.8 cm and height 1.5 cm has mass 119.5 g. Find its density.

• A rectangular solid with edge lengths 8.2 cm, 5.1 cm, and 4.7 cm has mass 153 g. Will it sink in water?

Chemical and Physical Changes

• Chemical change: Alters the chemical composition of a substance (e.g., burning, rusting).

• Physical change: Alters the form or appearance but not the chemical composition (e.g., melting, boiling).

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.

For example, in the combustion of acetylene:

Energy Changes: Endothermic and Exothermic

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

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

The Mole Concept

Definition and Avogadro's Number

The mole is a counting unit used in chemistry to express amounts of a chemical substance. One mole contains Avogadro's number of particles (atoms, molecules, ions):

particles

For any element, one mole of atoms has a mass in grams equal to the atomic mass listed on the periodic table.

Island Diagram

The island diagram is a visual tool for converting between grams, moles, and number of particles (atoms, molecules):

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

• Moles ↔ Particles: Use Avogadro's number ( particles/mol)

Example Problems

• How many moles is atoms of zinc?

• How many atoms is 0.68 moles of zinc?

• How many grams is 5.69 moles of uranium?

• How many grams is atoms of neon?

• How many atoms is 421 g of promethium?

Additional Info

• When calculating percent composition, use the formula:

• To find the mass of an element in a sample, multiply the percent composition (as a decimal) by the sample mass.