Transcript Document

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= Cathode
B= Anode
C= electrical source
D= Positively charged plate
E= negatively charged plate
• http://highered.mcgrawhill.com/sites/0072512644/student_view0/chapte
r2/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.mcgrawhill.com/sites/0072512644/student_view0/chapte
r2/animations_center.html#
New Zealand Scientist
Ernest Rutherford(18711937)
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/che
mistry/essentialchemistry/flash/rut
her14.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
Proton
Location
Inside
nucleus
Neutron Inside
nucleus
Electron Outside
nucleus
Charge(C)
Mass (g)
Mass
(amu)
1.602 x 10-19
1.673x10-24 1.0073
=1
0
1.675x10-24 1.0087
=1
-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!
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+
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 12
Number of electrons - 10
Charge of Ion 2+
Ion
19. Cu²+
Protons
Electrons
29
27
20. As3-
33
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 mass: weighted average of the
masses of the existing isotopes of an
element.
Atomic Number/
number of protons
Atomic mass
• What was Dalton’s 2nd Postulate?
• Was it correct?
Hmmm
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.
• 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
Mass number
141 2+
Ba
56
Charge
Atomic number
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
46
45
50
14
29
Atom or
Ion?
90 2+
38Sr
Atom
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
46
45
50
14
29
Atom or
Ion?
90 2+
38Sr
Atom