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Thursday, Oct. 20th: “A” Day Friday, Oct. 21st: “B” Day Agenda Chapter 2 Tests 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” “Happy Mole Day” video *Quiz over section 3.1 next class* Ch. 2 Test Class 3A 4A 2B 4B Average 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”. 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 H2O, NOT H3O1.5 Law of Multiple Proportions Example: when carbon and oxygen combine, they combine in ratios of small, whole numbers CO (carbon monoxide) CO2 (carbon dioxide) Atomic Theory Atomic theory: all matter is made up of atoms. In 1808, John Dalton came up with his own atomic theory…. 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. 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 Theory 4th 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 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 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… This is ALL stuff that we will cover in Ch. 3 Happy Mole Day! Mole day is October 23rd and occurs at precisely 6:02 in the morning and 6:02 in the evening. Scientists celebrate mole day because the mole is the SI base unit for the amount of a substance. The number of particles in 1 mole of any substance is 6.022 X 1023, which is Avogadro’s number. We will learn more about the mole in section 3.4 as we begin counting atoms…