Chem121-Chapter-2_Beekman

Chem121-Chapter-2_Beekman - Are You on Track? Quiz on...

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1 Are You on Track? Jesse Owens, by Paul Calle, 1998. • Quiz on Monday/Wednesday • By the time of your quiz you should have DONE : •All of the HW for Chapter 1 • ~ ½ of the HW for Chapter 2 • Review your lecture notes • Read Chapter 1 and ½ of Chapter 2 Chapter 2: Atoms, Molecules and Ions Fe on Cu © R. Spinney 2010
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2 The Atomic Theory of Matter 1. An element is composed of extremely small particles called atoms. 2. All atoms of a given element are identical and have identical properties. 3. Atoms cannot be created, destroyed, or transformed into another element by chemical reactions. 4. Compounds are formed when atoms of more than one element combine. Atomic Theory of Matter (cont’d) The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.
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3 Dalton’s Postulates All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Dalton’s Postulates (cont’d) Atoms are neither created nor destroyed in chemical reactions, nor changed into atoms of a different element .
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4 Dalton’s Postulates (cont’d) Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. Law of Constant Composition • This is also known as the Law of Definite Proportions. • The elemental composition of a pure substance never varies: – water is always H 2 O. – sucrose (sugar) is always C 12 H 22 O 11 .
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5 Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. You don’t destroy any atoms so they remain at the end, just is a different form, i.e. CH 4 + 2 O 2 CO 2 + 2 H 2 O Modern View of Atomic Structure • An atom is: the smallest particle of an element that retains all of the properties of that element. • Size of an atom: – Mass: 1 atomic mass unit (amu) = 1.66054 x 10 -24 g – Diameter: ~1 x 10 -10 to ~5 x 10 -10 m, or ~1 – 5 Å
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6 Picture of the Atom Nucleus: Contains Protons and Neutrons, most of the atom’s mass. Electron Cloud: Contains electrons, which are much smaller in mass. Determines reactivity of atom. Atoms (cont’d) • Atoms contain: protons, neutrons and electrons . • Protons & electrons (e - ) are charged. The e - charge is - 1, the proton charge is + 1. Neutrons have no charge (neutral )
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7 Atoms (cont’d) Protons and neutrons are ~1800 times the mass of an e - particle Mass (amu) Electronic charge location e - 5.468 x 10 -4 - 1 Outside nucleus proton 1.0073 + 1 nucleus neutron 1.0087 0 nucleus Atomic Symbols • Chemical symbols indicate the atom type, i.e. C is a carbon atom.
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Chem121-Chapter-2_Beekman - Are You on Track? Quiz on...

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