Bell Work On your bell work sheet, date

today’s entry:

1. If a cube has a side length of 2 m, what is it’s volume in cm3?

2. Using the correct Sig. Figs, evaluate the following: (36.2-2.1) ÷ 4.2

Be prepared to take notes

Lesson Preview

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

Chapter 3.1 Atomic Philosophy to 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.”

WHAT DID DEMOCRITUS PROPOSE ABOUT THE ATOM?

Atoms are small indestructible, indivisible particles.

Made of a single material that’s formed into different shapes and sizes.

They are always moving

They form different materials by joining together.

(Which of these statements do we now know are correct? Was Democritus pretty smart for someone who lived thousands of years ago?)

Democritus

Greek banknote with Democritus and drawing of atom

Where did Democritus get his ideas for

small, 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 matter

Aristotle 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

WHAT IS AN ATOM?An atom is the

smallest particle of an element that retains its properties.

For example the smallest particle of carbon is a single atom of carbon. If you divide it is no longer carbon anymore.

PIECES OF CARBON

CARBON ATOM

Foundations of Atomic Theory

•The change of 1 or more 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

Fig 2-5

Mass is neither created nor destroyed during physical or chemical processes.

Conservation of Atoms & Mass

Courtesy Patrick Watson

Foundations of Atomic Theory

•Law of definite proportions: a chemical compound has the same elements in exactly the same proportions.

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 Multiple Proportions

Law of Conservation of Mass

JOHN DALTON 1776-1844

Two thousand years later a British chemist and schoolteacher brings back Democritus’s idea of the atom

He performed many experiments to study how elements join together to form new substances

Created a Theory!

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.Atoms of the same element

are the same, different elements are different.

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 (on BW sheet)

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.