Download The Structure of the Atom

The Structure of the Atom
Mr. O’Brien (SFHS)
Chapter 4
Standard 1.E&A
Structure of an Atom
(std.1E)
(figure 1) Early model of an
atom. If atoms were empty
space then the experiment
would have showed no
deflection.
• What is the Earliest Idea of an Atom
– the atom was EMPTY SPACE with (-)
particles “floating around”.
• What is the Current Idea of an Atom?
– Rutherford Experiment.
• Exposed a thin gold foil to a stream of
particles.
• 99.8% of particels went through.
• 0.2% of particles were deflected or
bound back! THIS PROVED DISCOVERY
OF A VERY SMALL NUCLEUS!
(figure 2) ACTUAL RESULTS!
The particles bounced back.
Discovery of Nucleus!
(figure 2) Imagine the atom’s nucleus to be the
size of a bean, the atom itself will become the
size of a stadium. The electrons will be like tiny
fleas whizzing frantically somewhere around
the stands.
Structure of an Atom
(std. 1E)
 Atom: smallest particle of an element
that retains the properties of the
element.
– ex: Copper (Cu)
• There are 29,000,000,000,000,000,000,000
Copper atoms in a penny!
• What’s in an Atom?
 NUCLEUS
(figure 1) Illustrates the size of a nucleus
(the golf ball) and the distance between the
nucleus and the edge of an atom.
• tiny & dense center of an atom
• contains protons (+) charge particles
• contains neutrons (have NO CHARGES)
Cool Facts of the Nucleus
•100,000x smaller than its atom
•Contains 99.9% of the atoms mass
•Protons & neutrons have the same mass (1a.m.u.).
(figure 2) If there are
29,000,000,000,000,000,000
,000 atoms in one copper
penny, what does that say
about the size of one atom?
So What Does Atom Look Like???
 What is the net charge of the nucleus?
 ELECTRON CLOUD
• contains electrons (é) (-) charge particles
• Move very fast and unpredictable around
the nucleus
Cool Facts of the Electron Cloud
•An electron is 1/2000 a.m.u. the size of a proton.
BEST representation
Not a good
representation
Recap
Structure of an Atom
(std.1E)
• Atom is smallest particle that
retains element property.
• Atom is mostly made up of
empty space.
– Atom contains an electron cloud.
– Electrons are 2000x smaller than
a proton or neutron!
• Atom has a tiny dense core called
the nucleus.
– Nucleus is virtually all the mass of
the atom.
– Protons mass (1a.m.u.) = Neutron
mass (1a.m.u.)
– An atom can be up to 100,000x
bigger in diameter than the nucleus!
• Atom is electrically neutral:
– Electron charge (-1) cancels out
proton charge (+1)
Atoms & Isotopes
(std.1a)
• What makes elements unique from
each other?
• Atomic Number
• The number of protons in an atom.
• The atomic number can never be changed in
an element.
• The Periodic Table organizes all known
elements by increasing atomic number.
(figure 1) the image to the left
shows liquid nitrogen rapid
evaporating. Pencil lead is just one
product made from carbon atoms
• What unit is used to measure the mass of atoms?
• Atomic Mass Units (a.m.u.)
• Standard is based on 1/12 a carbon atom
Atoms & Isotopes
(std.1a)
• Is there more of than one type of
nitrogen or one type of carbon?
• Isotopes
• Atoms of the same element with different
number of neutrons but same number of
protons.
• Why is the mass number different than the
atomic mass on the periodic table?
• Atomic mass is an average of all isotopes.
• Mass number is the sum of the number of
protons + neutrons (of specific isotope)
• Why is carbon atomic mass 12.011
a.m.u.?
• More carbon-12 exist than any other
isotope.
• That’s why the average is closer to 12.
Atoms & Isotopes (std.1.A)
• How do you calculate number of particles?
• Protons are found on the periodic table (atomic
number)
• Neutron are found by subtracting protons from Mass
Number.
Mass number – protons = neutrons
• Electrons = protons = atomic number
isotope
Protons
Neutrons
electrons
Carbon-12
6
6
6
Carbon-13
6
7
6
Carbon-14
6
8
6
Experimental Discoveries (std.1H)
• The Discovery Recap:
– J.J. Thomson: Use a Cathode Ray
Tube to discover that gas particles
carried a negative charge.
– Robert Millikan: confirmed
Thomson’s experiment that electrons
are identical particles by balancing
tiny, electrically charged oil droplets
that separated into equal distances.
– Ernest Rutherford: Shot positive
alpha particles through gold foil and
discovered that atoms had positive
dense nucleus.
Calculating Atomic
Mass of Isotopes (hnrs)
Isotope Abundance for Element X
Isotope
Atomic Mass
% abundance
X6
6.015
7.5%
X7
7.016
92.5%
• Example: Calculate the atomic mass of unknown element X.
Then, identify the unknown element, which is used to medically
treat some disorders.
• 1st step: multiply mass of Isotope X6 by the percent abundance
(how much there is in the world). Do the same for Isotope X7.
– (6.015a.m.u.)(0.0750) = 0.451a.m.u.
– (7.016a.m.u.)(0.925) = 6.49a.m.u.
• 2nd step: Sum the mass contributions.
– (0.451a.m.u. + 6.490a.m.u.) = 6.941a.m.u.
• 3rd step: Match the new atomic mass with the periodic table.
– 6.941a.m.u. is Lithium.