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The Atom & Subatomic Particles
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What we knew by 1932: 1.0087 amu (or 1 amu) neutron 1n 1.0073 amu +1
neutron 1n amu +1 proton 1p or 1H amu (or 0 amu) -1 electron 0e Relative Mass Relative Charge -1 1 1
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Location of Subatomic Particles
electrons located outside nucleus protons & neutrons located inside nucleus
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Atomic Number atomic number: For neutral atoms:
= size of nuclear charge = number of protons in nucleus determines identity of element gives order to PT For neutral atoms: atomic number = # protons = # electrons
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Mass Number = # protons # neutrons
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Isotopes atoms of same element can have different mass numbers
# protons must be the same so … # neutrons must be different
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Dalton’s theory must be modified:
the atom is divisible presence of subatomic particles atoms of same element can be different isotopes have different # neutrons
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Notation 12C 6 left superscript is mass number
left subscript is atomic number
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Notation 12C 6 How many neutrons in this atom?
12 = # protons + neutrons 6 = # protons 12C 6 How many neutrons in this atom? 12 – 6 = 6 neutrons
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Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 17O 8 17 8 = 9 17 – 8 8
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15 N Mass number is ? Atomic number is ? # of neutrons is ? # of electrons in atom is? 7 15 7 15 – 7 = 8 7
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F 19 Mass number is ? Atomic number is ? # of neutrons is ?
# of electrons in atom is? 19 9 19 – 9 = 10 9
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Other Notations C-12 # after symbol is mass number! must look up atomic number
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What’s the difference between H-1, H-2, and H-3?
All H’s have 1 proton H-1: mass # = 1 1 proton, ? neutrons H-2: mass # = 2 1 1 proton, so it must have ? neutrons H-3: mass # = 3 2 1 proton, so it must have ? neutrons
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Consider U-234, U-235, & U-238 What’s the atomic number of U?
How many protons in U? How many neutrons in U-234? How many neutrons in U-235? How many neutrons in U-238? How many electrons in U? 92 92 234 – 92 = 142 235 – 92 = 143 238 – 92 = 146 92
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How many neutrons in Po-217?
What’s the atomic number? How many protons? So the neutrons are … 84 84 217 – 84 = 133 neutrons!
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IONS IONS = atoms that gained or lost electrons
protons and electrons aren't = anymore, so ions are not neutral they carry a charge (+/-)
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IONS Charge of ion: = # protons minus # electrons
(subtract the electrons since are negative)
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IONS If atom loses electrons, it has more (+) protons than (-) electrons What kind of ion is it? If atom gains electrons, it has more (-) electrons than (+) protons positive negative
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Charge of Ions Ion charge: right superscript
Cl-1 a chloride ion with a charge of -1 Na+1 a sodium ion with a charge of +1 O-2 an oxygen ion with a charge of -2 If no right superscript, it’s understood to be zero and therefore a neutral atom
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Putting it all together
How many protons, neutrons, & electrons in each of the following 23Na+1 Got 2 e- Lost 1 e- Got 1 e- 34S-2 19F-1 9 1 16 16 p, 18 n, 18 e 9 p, 10 n, 10 e 11 p, 12 n, 10 e Lost 2 e- Lost 2 e- 13N-3 Got 3 e- 25Mg+2 64Zn+2 12 30 7 7 p, 6 n, 10 e 30 p, 34 n, 28 e 12 p, 13 n, 10 e
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What is an amu? atomic mass unit amu 1/12 the mass of the C-12 atom
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