Monday, Oct. 21 st : “A” Day Tuesday, Oct. 22 nd : “B” Day Agenda Begin Chapter 3: “Atoms and Moles” Sec. 3.1: “Substances are Made of Atoms” In-Class:

Monday, Oct. 21st: “A” DayTuesday, Oct. 22nd: “B” Day

Agenda

Begin Chapter 3: “Atoms and Moles”Sec. 3.1: “Substances are Made of Atoms”In-Class: Sec 3.1 review, pg. 78: #1-8Movie: “Atoms: The Building Blocks of Matter”

Homework: Concept Review: “Substances Are Made of Atoms”

*Quiz over section 3.1 next time*

Ch. 2 Tests“Matter and Energy”

ClassAverage Score

(out of 60)Average

Percentage

2A 48.52 80.87 %

4A 51.93 86.55 %

1B 52.00 86.67 %

3B 53.32 88.87 %

Our Understanding of Atoms Required Many Centuries

As early as 400 B.C.E. the Greek philosopher Democritus identified invisible units of matter called “atoms”.

The problem: Democritus was unable to provide scientific data to convince people that atoms really did exist.

Most people believe that an atom looks like the picture on the left. The diagram on the right

is a much better model of the atom.

Law of Definite ProportionsThe law of definite proportions: a chemical

compound always contains the same elements in exactly the same proportions by weight or mass.

Every molecule of a substance is made of the same number and types of atoms.

Example: NaCl is ALWAYS 39.34% Na and 60.66% Cl

Law of Conservation of MassThe law of conservation of mass: mass

cannot be created or destroyed in ordinary chemical and physical changes.

Example: in chemical reactions, the mass of the reactants is equal to the mass of the products.

Law of Conservation of Mass

Law of Multiple ProportionsThe law of multiple proportions: when two elements

combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small, whole numbers.

Example: Water is H2O, not H1.5OExample: When carbon and oxygen combine, they

combine in small, whole number ratiosCO (carbon monoxide) 1:1 ratioCO2 (carbon dioxide) 1:2 ratio

Law of Multiple Proportions

NO (nitrogen monoxide) 1:1 ratioNO2 (nitrogen dioxide) 1:2 ratio

Atomic TheoryAtomic theory: all matter is made up of

atoms.

In 1808, John Dalton revised the early Greek idea of atoms into a scientific theory that could be tested by experiments.

5 Principles of Dalton’s Atomic Theory1. All matter is made of extremely small particles called

atoms, which can’t be subdivided, created, or destroyed.

2. Atoms of a given element are identical in their physical and chemical properties.

3. Atoms of different elements differ in their physical and chemical properties.

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

5. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed.

Problems with Dalton’s Atomic Theory Data obtained since Dalton’s time shows that the first 2

principles are NOT true in all cases.

1st principle: all matter is made of extremely small particles called atoms, which can’t be subdivided, created, or destroyed.

The atom CAN be divided into smaller particles. What are they?

Scientists have also been able to destroy and create atoms using technology.

Problems with Dalton’s Atomic Theory

2nd principle: atoms of a given element are identical in their physical and chemical properties. Isotopes of the same element have different

atomic masses

Problems with Dalton’s Atomic Theory4th principle: atoms of different elements

combine in simple, whole number ratios to form compounds.Dalton didn’t know that atoms of the SAME

element can also combine with each other. (O2, N2, S8, H2, Cl2)

The 4th principle principle isn’t wrong, it’s just missing some information.

Dalton’s Atomic TheoryDalton’s theory continues to be modified and

expanded as scientists learn more and more about atoms.

In-Class AssignmentSec 3.1 review

Pg. 78: #1-8

Homework: Concept Review:

“Substances are Made of Atoms”

*Be ready for a quiz over this section next class period*

Movie: “Atoms, the Building Blocks of Matter”Get out a piece of paper and write down 10

things that you learned from the movie…

Yes, this IS for a grade.

This is ALL material that wewill be covering in chapter 3…