Learning Target Analyze and explain Rutherford’s Gold Foil Experiment.
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Transcript of Learning Target Analyze and explain Rutherford’s Gold Foil Experiment.
Learning Target• Analyze and explain Rutherford’s Gold Foil
Experiment.
Comparison of Atomic Models
Dalton’s Model
Thomson’s Model Rutherford’s Model
J.J. Thomson (IN 1896)A= CathodeB= Anode C= electrical sourceD= Positively charged plateE= negatively charged plate
• http://highered.mcgraw-hill.com/sites/0072512644/student_view0/chapter2/animations_center.html#
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#
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.
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
Rutherford experiment animation
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Rutherford’s Atomic Structure Model
+ =positively charged particles- = electrons
• YOU WILL NEED:
–NOTEBOOK
–PERIODIC TABLE
• 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
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
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
• 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.
Electron Number
• An Element’s atomic number also indicates number of electron in its atoms.
Ions
•Ions are atoms that have lost or gained one or more electrons giving them a positive or negative charge!
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.
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+
19. Cu²+
20. As3-
29
33
Ion Protons Electrons
27
36
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
Differences between isotopes?
• Isotopes react in the same way as others of the same element
Atomic massAtomic Number/number of protons
Atomic mass: weighted average of the masses of the existing isotopes of an element.
• What was Dalton’s 2nd Postulate?
• Was it correct?
Hmmm
• 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
• 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?
Complete Chemical Symbols
14156
Mass number
Atomic number
ChargeBa2+
Number of protons = Atomic #Number of neutrons = Mass # - Atomic #Charge = Atomic # – Number of electrons
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
WARM UP
• What is the atomic mass unit of a proton? Neutron? Electron?
• What is the atomic mass of an element represent?
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