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Learning Target• Analyze and explain Rutherford’s Gold Foil
Experiment.
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Comparison of Atomic Models
Dalton’s Model
Thomson’s Model Rutherford’s Model
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J.J. Thomson (IN 1896)A= CathodeB= Anode C= electrical sourceD= Positively charged plateE= negatively charged plate
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• http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#
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Robert Millikan - 1909
• He measured the charge of an electron.• Using this he gave a negative charge to oil
droplets and was able to measure how different charged plates changed the droplets rate of fall.
• This also allowed him to measure the mass from the charge to mass ratio.
http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#
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New Zealand Scientist Ernest Rutherford(1871-1937)
Had performed experiments to find that atoms were made of positively charged particles moving around a very tiny positively charged nucleus.
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Rutherford’s Gold Foil experiment
He did an famous experiment whereby he shot a stream of alpha particles at a thin piece of gold (Au) foil expecting most of the particles to be deflected-instead most of them passed directly through the foil and onto the photographic film
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Rutherford experiment animation
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Rutherford’s Atomic Structure Model
+ =positively charged particles- = electrons
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• YOU WILL NEED:
–NOTEBOOK
–PERIODIC TABLE
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• Protons (positive) are bigger than electrons. The part of an atom that gives an element its identity.
• Neutrons (neutral) are slightly bigger in mass than a proton.
• Electrons (negative) charge, have a mass of close to zero-negligible
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Atomic Mass Units (amu): roughly equal to the mass of a proton or neutron.**the mass of an atom is measured in amu’s
1 amu = 1.66x10-24g
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Particle Location Charge(C) Mass (g) Mass (amu)
Proton Inside nucleus
1.602 x 10-19 1.673x10-24 1.0073=1
Neutron Inside nucleus
0 1.675x10-24 1.0087=1
Electron Outside nucleus
-1.602 x 10-14 7.109x10-28 0.0006=0
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• Every element has a unique atomic number which is the number of protons in the atom.
• Elements atomic number is just above the chemical symbol on periodic table.
• Atoms are electrically neutral-means number of protons always equal number of electrons.
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Electron Number
• An Element’s atomic number also indicates number of electron in its atoms.
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Ions
•Ions are atoms that have lost or gained one or more electrons giving them a positive or negative charge!
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For example: Na (Sodium), has originally 11 electrons but when an electron is lost it becomes a positive ion. Na+
If an ion loses an electron it has a positive charge.
If an ion gains an electron it has a negative charge.
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A neutral magnesium atom (atomic number=12) has 12 protons/electrons. If it loses 2 electrons it becomes an ion with a charge of 2+.
Number of protons 12Number of electrons - 10 Charge of Ion 2+
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19. Cu²+
20. As3-
29
33
Ion Protons Electrons
27
36
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Isotopes• Isotopes are atoms that have the same
number of protons but different numbers of neutrons
• Most elements in the first two rows of the periodic table have at least 2 isotopes with one being more common than the other
• In nature, elements are almost always found as a mixture of isotopes
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Differences between isotopes?
• Isotopes react in the same way as others of the same element
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Atomic massAtomic Number/number of protons
Atomic mass: weighted average of the masses of the existing isotopes of an element.
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• What was Dalton’s 2nd Postulate?
• Was it correct?
Hmmm
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• The most common isotope of hydrogen has no neutrons at all
• There's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.
Isotopes of Hydrogen
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• To identify an isotope more specifically, chemists add a number after the elements name.
ex. Carbon-11 Carbon-12 Carbon-14
• This number is called the isotope’s mass number and is the sum of the isotope’s number of protons and neutrons.
• What is the atomic mass on your Periodic Table?• Which of the 3 isotopes of Carbon is the most
abundant?
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Complete Chemical Symbols
14156
Mass number
Atomic number
ChargeBa2+
Number of protons = Atomic #Number of neutrons = Mass # - Atomic #Charge = Atomic # – Number of electrons
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Complete the Table
Chemical Symbol
No. of Protons
No. of Electrons
No. of Neutrons
Atom or Ion?
38Sr2+
46 45 50
14 29 Atom
90
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WARM UP
• What is the atomic mass unit of a proton? Neutron? Electron?
• What is the atomic mass of an element represent?
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Complete the Table
Chemical Symbol
No. of Protons
No. of Electrons
No. of Neutrons
Atom or Ion?
38Sr2+
46 45 50
14 29 Atom
90
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