CHEM10 Chapter 3 Part 1

Introduction to Atoms

  • Start of Chapter Three

    • Focus on chemistry

    • Understanding matter

    • Importance of pacing

    • Review previous chapters, especially math elements

Overview of Matter

  • All matter consists of atoms

  • Atoms are building blocks of everything

  • 118 known elements

    • Approximately 98 naturally occurring elements

Concept of Atoms

  • Atoms as fundamental units of matter

  • Each atom type has unique properties

  • Comparison to Lego blocks

    • Different colors = different types

    • Combining forms new compounds

  • Chemistry is everywhere

    • Integral to understanding material world

Historical Perspective

  • "Atom" from Greek "atomos"

  • Democritus (400 BCE) theorized indivisible particles

  • Dormant understanding from 400 BCE to 1700s

    • Renaissance advancements explored chemistry systematically

  • Antoine Lavoisier

    • Established law of conservation of mass in late 1700s

    • Mass unchanged in closed systems during reactions

The Law of Conservation of Mass

  • Mass is neither created nor destroyed in reactions

  • Example: Combining hydrogen (H₂) and oxygen (O₂)

    • Forms water (H₂O)

    • Mass consistent before and after

  • Chemical reactions maintain mass

Dalton's Atomic Theory (1808)

  • John Dalton's key concepts:

    • Elements consist of tiny, indivisible particles (atoms)

    • Unique atoms for each element

    • Atoms combine in whole number ratios (e.g., water: 2H + O)

    • Atoms rearranged in reactions, not changed or lost

Chemical Reactions and Changes

  • Example: Charcoal burning

    • Carbon (C) + Oxygen (O₂) = Carbon Dioxide (CO₂)

    • Atoms retain identity and properties despite reconfiguration

The Periodic Table (1860s)

  • Dmitry Mendeleev arranged elements by atomic mass and properties

    • Led to predictions about undiscovered elements

  • Modern periodic table based on atomic number and properties

    • Provides insights into chemical behavior

Structure and Properties of Elements

  • Elements classified:

    • Metals: Left side; good conductors; solid at room temperature (e.g., iron, gold)

    • Non-metals: Upper right; varied physical states (e.g., sulphur, bromine, oxygen)

    • Metalloids: Between metals and non-metals; semiconductors (e.g., silicon)

Families of Elements

  • Alkali Metals (Group 1A)

    • Soft metals; react vigorously with water

  • Alkaline Earth Metals (Group 2A)

    • Less reactive; used in fireworks (e.g., magnesium)

  • Halogens (Group 7A)

    • Diatomic molecules; react with metals/non-metals

  • Noble Gases (Group 8A)

    • Chemically inert; stable configurations

Discovery of Subatomic Particles

  • Subatomic particles:

    • Protons: positive

    • Neutrons: neutral

    • Electrons: negative

  • J.J. Thomson: Discovered electrons (1897)

    • Crucial for electricity and chemistry

  • Rutherford’s Gold Foil Experiment

    • Revealed dense nucleus surrounded by mostly empty space

    • Led to modern nuclear model of the atom

Modern Atomic Structure

  • Protons: Mass ~1 amu, positive charge

  • Neutrons: Mass ~1 amu, no charge

  • Electrons: Mass ~0.0005 amu, negative charge

  • Arrangement of particles determines behavior and properties