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: Sec 3.1 review, pg. 78: #1-8  Movie: “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” Class Average Score (out of 60) Average Percentage 2A % 4A % 1B % 3B %

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 Proportions  The 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 Mass  The 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 Proportions  The 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 H 2 O, not H 1.5 O  Example: When carbon and oxygen combine, they combine in small, whole number ratios CO (carbon monoxide) 1:1 ratio CO 2 (carbon dioxide) 1:2 ratio

Law of Multiple Proportions NO (nitrogen monoxide) 1:1 ratio NO 2 (nitrogen dioxide) 1:2 ratio

Atomic Theory  Atomic 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 Theory 1.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.  1 st 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  2 nd 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 Theory  4 th 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. (O 2, N 2, S 8, H 2, Cl 2 ) The 4 th principle principle isn’t wrong, it’s just missing some information.

Dalton’s Atomic Theory  Dalton’s theory continues to be modified and expanded as scientists learn more and more about atoms.

In-Class Assignment  Sec 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 we will be covering in chapter 3…