Bell Work On your bell work sheet, date today’s

entry:1. How many Sig. Figs. are in 9520000?2. Using the correct Sig. Figs, evaluate

the following: 3.12 + 9.325If you didn’t get a book, come see me.Open your book to page 66 and begin

reading.

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Lesson StarterObjectivesFoundations of Atomic TheoryLaw of Conservation of MassLaw of Multiple ProportionsDalton’s Atomic TheoryModern Atomic Theory

Chapter 3.1 Atomic Philosophy to Theory

Think about it…•Young people should not smoke.•Smoking at an early age may make it more difficult to quit smoking later.oWhich of the above statements is an opinion and which is a theory?

Objectives•Explain the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

•Summarize the five essential points of Dalton’s atomic theory.

•Explain the relationship between Dalton’s atomic theory and the law of conservation of mass, the law of definite proportions, and the law of multiple proportions.

It Started with the GreeksDEMOCRITUS

• Lived in Greece 2500 years ago.• “Father of modern science”• He said: “All matter is made of atoms that are tiny, indestructible and indivisible.”

Democritus

Greek banknote with Democritus and drawing of atomWhere did Democritus get his

ideas forsmall, indestructible,

indivisible atoms?

Atoms are small…

new wedding rings old wedding ring

EVIDENCE: Old wedding rings get worn away slowly, and get thinner and thinner, but you never see the gold atoms on your finger, so gold atoms must be very small!

Atoms are indestructible…

Atoms are indivisible…

EVIDENCE: The Earth has been around a long time. Even though mountains get washed away, the rocks continue to exist. New plants grow where old plants die. EVIDENCE: None.This was a HYPOTHESIS made by Democritus to explain nature as he saw it.

Aristotle had other ideas

ARISTOTLE: Famous Greek philosopher, born 384 BCE. He was a student of Plato (another famous philosopher) and the teacher of Alexander the Great, who later conquered the world.

Greek banknote and coin picturing Aristotle

Aristotle’s idea of matterAristotle did not believe that Democritus’s idea of atoms was correct.

He believed all matter was made from four elements:

EarthAirFireWater

Aristotle’s idea of matterAristotle was more famous than Democritus, so people believed him, even though he was wrong.

So Democritus’s idea of atomos (atoms) was lost for nearly 2000 years until John Dalton brought it back in 1803.

Atom idea lost for ~2000 years

Foundations of Atomic Theory

•The transformation of a substance or substances into one or more new substances is known as a chemical reaction.

•Law of conservation of mass: mass is neither created nor destroyed during ordinary chemical reactions or physical changes

Foundations of Atomic Theory

•Law of definite proportions: a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound

Foundations of Atomic Theory•Law of multiple proportions: if two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers

Law of Conservation of Mass

Law of Multiple Proportions

John Dalton, New Atom,1803

Born in England, 1766.

Studied chemistry, physics, and color blindness.

Brought back Democritus’s idea of an indivisible atom.

Dalton’s Atomic Theory

1.All matter is composed of extremely small particles called atoms.

2.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

3.Atoms cannot be subdivided, created, or destroyed.

Dalton’s Atomic Theory, continued

4.Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

H2O (2:1)5.In chemical reactions, atoms

are combined, separated, or rearranged.

2H2O + 2Na 2NaOH + H2

Modern Atomic Theory

• Not all aspects of Dalton’s atomic theory have proven to be correct. We now know that:

Atoms are divisible into even smaller particles.A given element can have atoms with

different masses.• Some important concepts remain unchanged.All matter is composed of atoms.Atoms of any one element differ in properties from atoms of another element.

Reflection (write it out)

1. The fact that every sample of a particular chemical compound contains the same elements in exactly the same proportions by mass is known as the law of

a)conservation of energy.b)conservation of mass.c) atomic theory.d)definite proportions.