Download Atomic Structure

Atomic Structure and The
Periodic Table
Mr. Chan
Northwestern University
Today (Day 18)
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(0-10) Return/Discuss Tests
(10-15) Activate: Sketch Atom
(15-20) Mystery Box
(20-30) Dalton’s Atomic Theory
(30-43) Word Splash
Video – WOC The Atom (30 min)
 Conferences
Mystery Boxes
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Procedure:
Select a Mystery Box. Without opening it,
try to learn about its contents by using all
the tools of observation available to you.
Outline your plan to determine the
contents of the box and record all
observations you make.
Mystery Boxes
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Questions:
1. What evidence supports your conclusion
about the type of item contained in the box?
2. What kinds of things can you do to determine
the contents of your box if you had access to
other kinds of observational tools?
3. Since you cannot see what is inside, how can
you be 100% sure of its contents?
What are atoms?
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Smallest particle of element that retains properties of the
element
Possible to see individual atoms
Demo: Al Foil – Physical Changes – Smallest Piece
History of Atomic Theory
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Original model – Democritus
 Atomos – smallest unit of matter
Dalton’s Theory
 1) Elements composed of tiny indivisible (not
invisible) particles called atoms
 2) Atoms of the same element are identical
 3) Atoms of different elements can chemically combine
with one another in simple whole number ratios
(compounds)
 4) In chemical reactions, atoms are separated, joined,
and rearranged. Atoms of one element are never
changed.
Today (Day 19)
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(0-5) Discuss HW
(5-10) Demo
(10-25) Experiments – discovery of Atomic Structure
(25-35) Rutherford’s Au Experiment
(35-43, 0-25) LAB
(25-43) Numbers associated with At.Structure
What is the structure of an atom?
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Electrons
 J.J. Thomson, cathode ray tubes – Overhead
 Electric current flowing through gases
 Beam – cathode ray travels from cathode (-) to
the anode (+)
 Metal plates – beam attracted to positive plate
 Electrons: negative, 1/2000 mass of hydrogen
atom
 Millikan – oil drop experiments
 determined charge/mass ratio of electron
 Mass of electron = 1/1840 mass of hydrogen
atom
Structure cont.
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Protons – positively charged particles
 Needed to balance charge of electrons in atom
 Goldstein – CRT with loss of electrons – canal rays
from cathode traveling in opposite direction as
electrons
Neutrons – no charge, mass - proton
 Chadwick – knew some mass was unaccounted for
Summary of Subatomic particles
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Particle, symbol, relative charge, relative mass,
actual mass
Rutherford’s Gold Foil Experiment
Rutherford’s Gold Foil Experiment
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Led to discovery that most of the atom is empty space
All of the positive charge and most of the atom’s
mass found in a small region
Nucleus of the atom
 Core that contains protons and neutrons
Models of Atoms
Numbers Associated with Atomic Structure
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Atomic Number
 Number of protons in nucleus of atom of element
 Also equals number of electrons if electrically
neutral
 Determines which element you have
 Practice: How many protons and electrons, what
the symbol, element name is
Mass number
 Total number of protons and neutrons
 Not given on the periodic table
Calculating Number of Protons, Neutrons, and
Electrons
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Number of neutrons = Mass Number – Atomic
Number
Shorthand Notation: Mass/Atomic – Element
OR Element – Mass number
Practice #9-12: Determine number of protons,
electrons, and neutrons, completing tables of atomic
number, mass number, #protons, #neutrons,
#electrons, symbol – notation, Determining from
symbol: #neutrons
Today (Day 20)
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(0-5) Opener
(5-15) Discuss HW
(15-30) Quiz
(30-43) Isotopes
What are Isotopes?
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Atoms that have the same number of protons
but different numbers of neutrons
Different mass numbers
Atoms are chemically alike – behave similarly
 Common misconception: radically different
– NO!
Examples: 3 isotopes of hydrogen
 Tritium – Spiderman 2 errors – MOVIE
CLIP
 Gas, not solid
Today (Day 21)
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(0-10) Opener/Discuss HW
(10-15) Discuss QUIZ
(15-20) Spiderman 2 Clip
(20-30) Activity: Isotope Numbers Relay Race
(30-43) Average Atomic Mass
(0-43) Isotopes and Atomic Mass Lab
Opener - 9/29
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Determine the number of protons, neutrons, and
electrons in the following isotopes:
 Hydrogen-1, Hydrogen-2, and Hydrogen-3
What is average atomic mass?
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Weighted grades analogy
Masses of subatomic particles ridiculously small –
needed something more convenient
Arbitrary amount set: Carbon-12 atom = 12.00000
amu
1 amu (atomic mass unit) = 1/12 mass of C-12 atom
Mass of a single proton/neutron – 1 amu
Why are the masses decimals?
 Most elements exist as a mixture of 2 or more
isotopes
Look at average atomic masses of elements – can you
speculate which isotope is most common?
How do you calculate average
atomic mass?
 Average atomic mass =
weighted average mass of
atoms in naturally occurring
sample
Number on Periodic Table –
explains why we could not use
as mass number
 Reflects both the mass and the
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Today (Day 22)
Read Article
 Socratic Seminar
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Today (Day 24)
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Review
Today (Day 25)
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Chapter 4 Test
Origin of Periodic Table
Mendeleev
 Listed elements in
columns and in order of
increasing atomic mass
 Elements in groups with
similar properties
 Moseley
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Organization of Periodic Table
Increasing atomic number
 Periods
 Horizontal rows
 Groups
 Vertical columns of elements
 Periodic law
 Repetition of chemical and
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