Introduction to Matter

Definitions and Properties

Matter is anything that has mass and occupies space (volume). All physical objects are composed of matter, which can exist in different forms and states.

• 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. For example, copper (Cu) is made of copper atoms; water (H2O) is made of hydrogen and oxygen atoms bonded together.

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

Classification of Matter

Elements and Compounds

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

• Monatomic elements: Consist of single, unbonded atoms (e.g., He, Ne).

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

• Diatomic elements: Elements that naturally exist as molecules of two atoms (e.g., H2, 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).

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

• Example: Na (sodium, a reactive metal) and Cl2 (chlorine, a toxic gas) combine to form NaCl (table salt), which is safe to eat.

• Atoms can only be altered by chemical means; molecules can be altered by physical or 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 where particles settle over time (e.g., muddy water).

Contrast: 24K gold is pure (element), while 14K gold is an alloy (mixture).

Chart for Classifying Matter

Separating Mixtures

Mixtures can be separated by physical means or physical changes, including:

1. Sorting: Separating based on physical characteristics (size, color, shape).

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 of a substance per unit volume. It is a physical property that is nearly constant for a given substance under constant conditions.

Formula:

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

• **Density of water:** 1.00 g/mL at 4°C.

Density Calculations

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

2. Another sample of lead occupies 16.2 cm3 of space. Find sample's mass (if density is known).

3. A 119.5 g solid cylinder has radius 1.8 cm and height 1.5 cm. Find sample's density.

   • Volume of cylinder:

4. A 153 g rectangular solid has edge lengths 8.2 cm, 5.1 cm, and 4.7 cm. Will this object sink in water?

   • Volume:

Properties of Matter

• 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

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

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).

The Mole Concept

Counting Atoms: The Mole

Atoms are extremely small, so chemists use the mole as a counting unit. One mole (1 mol) contains particles (Avogadro's number).

• 1 mole of atoms = atoms

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

Island Diagram

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

• Mass (g) ↔ Moles (mol) ↔ Particles (atoms, molecules)

• 1 mol = particles

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?

4. How many grams is atoms of neon?

5. How many atoms is 421 g of promethium?

Summary Table: Elements vs. Compounds

Key trend: Elements are the simplest substances; compounds are combinations of elements with new properties.

Additional info: Some explanations and examples have been expanded for clarity and completeness.