Chapter 4 The structure of the atom. Atom Smallest part of an element that retains the properties of...
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Transcript of Chapter 4 The structure of the atom. Atom Smallest part of an element that retains the properties of...
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Chapter 4
The structure of the atom
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Atom
• Smallest part of an element that retains the properties of the element
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Democritus:Greek (460-370 BC)
• Proposed the first atomic theory
• called the tiny individual particles “atomos”
• Aristotle said that he was wrong
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John Dalton: Eng (1766-1844)
• School teacher• 1808- proposed the
first accepted atomic theory
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Joseph John (J.J) Thomson
• English physicist (1856-1940)
• 1897- used the cathode ray tube experiment to discover the electron
• Called plum pudding model
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Robert A. Millikan
• American Physicist-(1868-1953)
• 1909- used the oil droplet experiment to determine the charge of an electron and calculate the mass of the electron
• 1923- Nobel Prize• Thomson’s and Millikan’s
works was combined to conclude there must be a positive particle- equal in charge, but more massive than the electron
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Ernest Rutherford
• New Zealander (1871-1937)
• 1911- Gold Foil experiment- proved the atom was mostly empty space
• Concluded there was small positive center and called it the nucleus
• “discovered” and named the nucleus
• 1908- Nobel Prize
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James Chadwick
• English (1891-1974)• 1932- discovered the
neutron
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• Subatomic particles= electron, proton, neutron
• Nuclear forces- short range forces that hold nuclear particles together
• Atomic number = number of protons in an atom– In a neutral atom = # of
electrons
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Mass number
• Sum of the protons and neutrons in a nucleus
• Mass number – atomic number = neutrons
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Average atomic mass
• Weighted average of the atomic masses of the naturally occurring isotopes of an element
• # on chart• (%)(mass)+ %(mass)= average mass
Example: Carbon
mass number exact weight
percent abundance
12 12.00 98.90
13 13.00 1.10
(12.00) (0.98) + (13.00) (0.01) = 12.011
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isotope
• Same element, same number protons, same number electrons, different number of neutrons
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Methods of writing isotopes
Nuclear form and hyphen form
Nuclear form=Mass
atomic #
126 C
Hyphen= name-massEx. Carbon-12, carbon-14
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Atomic mass unit (AMU)
• 1/12 of the mass of a C-12 atom
• Not exactly 1 proton or 1 neutron
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Nuclear reactions
• Reactions which involve as change in an atoms nucleus
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Radioactivity
• Substances spontaneously emitting radiation
• Radiation- rays and particles
• Radioactive substances decay until they become stable
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4 types of radiation
2.Beta particle- fast moving electron
3. Gamma rays- high energy radiation4.Positron- same mass as electron with (+) charge
Proton decays to a positron and a neutron
1.Alpha particle- a helium nucleus 2 protons and 2 neutrons
0
-1e
4
2He
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The Mole
• Equal to the number of particles in exactly 12g of carbon-12
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3 equivalents of 1 mole
1. Molar mass: gram atomic mass, formula mass, molecular mass
• Mass number from chart• Add for compounds
Calculate the molar mass of Al(NO3)3
(1 x 27) + (3 x 14) + (9 x 16) = 213.00 g/mol213.00 grams is the mass of one mole of aluminum nitrate.
213.00 grams of aluminum nitrate contains 6.02 x 10^23 entities of Al(NO3)3
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2. Avogadro’s number of representative particles
• 6.022 x 1023
• Elements = atoms• Ionic = formula units• Covalent = molecules
Ex: One mole of donuts contains 6.022 x 1023 donuts
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3. 22.4 L of a gas at STP
• Standard temp= 0o C, 273 K
• Standard pressure= 1atm, 760 mmHg, 760 torr, 101.325 kPa