Untitled Flashcard Set

⚛ 1. Early Ideas of Matter

Before scientists had modern experiments, Greek philosophers tried to explain what everything is made of.

Thales

  • Said the basic substance of everything is water.

  • Believed all matter came from or was based on water.

Anaximander

  • Proposed the “apeiron”, meaning boundless/infinite.

  • Believed matter came from an unlimited, indefinite substance.

Anaximenes (if included in your lesson)

  • Said air was the basic substance of everything.

  • Different forms of matter came from air through compression and expansion.

Heraclitus

  • Believed fire was the fundamental substance.

  • Said everything is constantly changing.

Xenophanes

  • Believed the basic substances were earth and water.

  • Questioned traditional explanations of nature and mythology.

Aristotle

  • Believed matter was continuous, meaning it could be divided endlessly.

  • Proposed that matter was made from four elements:

  • 🌍 Earth

  • 💧 Water

  • 🌬 Air

  • 🔥 Fire

  • Also associated the elements with qualities such as hot, cold, wet, and dry.

⚛ 2. Democritus and Leucippus

Leucippus and Democritus proposed that matter is made of tiny particles called atoms.

Atomos = “indivisible”

They believed:

  • Matter is made of tiny, indivisible particles.

  • Atoms move through empty space (void).

  • Different substances have different atoms.

  • Atoms cannot be created or destroyed.

⚠ Their idea was philosophical, not based on experimental evidence.

🔬 3. Atomic Theories

Dalton's Modern Atomic Theory

In the early 1800s, John Dalton developed the first modern scientific atomic theory based on experimental evidence.

Dalton's Solid Sphere Model

Dalton pictured an atom as a:

small, solid, indivisible sphere

Basically:

⚫

There were no electrons, protons, or neutrons in his model yet.

📜 4. Dalton's Original Postulates

Postulate 1

All matter is composed of extremely small particles called atoms.

Postulate 2

Atoms of the same element are identical in their properties and mass.

Atoms of different elements have different properties and masses.

Postulate 3

Atoms cannot be created, destroyed, or divided during a chemical reaction.

Postulate 4

Atoms combine in simple whole-number ratios to form compounds.

Postulate 5

Atoms are rearranged during chemical reactions.

✏ 5. Amended/Modified Dalton Postulates

Some of Dalton's ideas were later changed because scientists discovered subatomic particles and isotopes.

Original:

Atoms are indivisible.

Amended:

Atoms can be divided into smaller particles:

  • Protons (+)

  • Neutrons (0)

  • Electrons (−)

Original:

Atoms of the same element are identical in mass.

Amended:

Atoms of the same element can have different masses because of isotopes.

Example:

Carbon-12 and Carbon-14

Both are carbon, but they have different numbers of neutrons.

What stayed true?

Dalton's theory still correctly established that:

  • Matter is made of atoms.

  • Elements consist of atoms.

  • Atoms combine to form compounds.

  • Chemical reactions involve the rearrangement of atoms.

🧠 SUPER SHORT MEMORY GUIDE

Thales → Water 💧

Anaximander → Apeiron ♾

Heraclitus → Fire 🔥 / Change

Xenophanes → Earth + Water 🌍💧

Aristotle → 4 Elements 🌍💧🌬🔥

Leucippus + Democritus → Atoms ⚫

Dalton → Modern Atomic Theory ⚫

Dalton's model:

Atom = solid sphere

Amended:

Atom → proton + neutron + electron

Same element ≠ always same mass → isotopes