Learning Target

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Learning Target

• Analyze and explain Rutherfords Gold Foil
  Experiment.

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Comparison of Atomic Models
Daltons Model
Thomsons Model
Rutherfords Model
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J.J. Thomson (IN 1896)
A Cathode B Anode C electrical source D
Positively charged plate E negatively charged
plate
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• http//highered.mcgraw-hill.com/sites/0072512644/s
  tudent_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/s
  tudent_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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Rutherfords 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/essentialche
mistry/flash/ruther14.swf
Rutherfords 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 amus
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 1.00731
Neutron Inside nucleus 0 1.675x10-24 1.00871
Electron Outside nucleus -1.602 x 10-14 7.109x10-28 0.00060
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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 Elements 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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If an ion gains an electron it has a negative
charge.
If an ion loses an electron it has a positive
charge.
For example Na (Sodium), has originally 11
electrons but when an electron is lost it becomes
a positive ion. Na
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A neutral magnesium atom (atomic number12) has
12 protons/electrons. If it loses 2 electrons it
becomes an ion with a charge of 2. Number of
protons 12 Number of electrons - 10 Charge of
Ion 2
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Ion
Electrons
Protons
19. Cu² 20. As3-
29 33
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 mass weighted average of the masses of
the existing isotopes of an element.
Atomic Number/ number of protons
Atomic mass
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• What was Daltons 2nd Postulate?
• Was it correct?

Hmmm
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Isotopes of Hydrogen

• 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.

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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 isotopes mass number
  and is the sum of the isotopes 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
141
Mass number
Ba2
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Charge
Atomic number
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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