Chem121-Chapter-2-SH

Chem121-Chapter-2-SH - Chapter 2: Atoms, Molecules and Ions...

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Chapter 2: Atoms, Molecules and Ions Fe on Cu © R. Spinney 2009 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 that differ from those of other elements. 3. Atoms cannot be created, destroyed, or transformed into atoms of another element by chemical reactions. 4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms. 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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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 of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. 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.
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Law of Constant Composition • This is also known as the Law of definite proportions. 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. 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 = 100 to 500 pm = 1 – 5 Å (angstrom) where 1 Å = 10 -10 m
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Atoms (cont’d) • Atoms contain: protons, neutrons and electrons. • Protons & electrons (e - ) are charged! – Charge = 1.602 x 10 -19 coulombs. – “Electronic charge” = charge on 1 e - e - charge is - 1, proton charge is + 1 neutrons have no charge (neut ral) Atoms (cont’d) • Protons and neutrons are ~1837 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. • Nuclear symbols include info on the composition of the nucleus: –Z = –A = –E = • For a neutral atom # protons = # e -
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Atomic Symbols (cont’d) E A Z Mass number superscript Atomic number subscript Ag 107 47 A silver atom with 47 protons, 60 neutrons And 47 electrons Atomic Numbers and Mass Numbers • Since both the atomic number (Z) and element symbol (E) define the same thing (a unique type of atom) the atomic number is commonly omitted Î 107 Ag. •T
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This note was uploaded on 04/04/2009 for the course CHEM 121 taught by Professor Wyzlouzil during the Spring '07 term at Ohio State.

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Chem121-Chapter-2-SH - Chapter 2: Atoms, Molecules and Ions...

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