Download Chp 4 PPT final

The Structure of an Atom
4.2
The Element Song
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http://www.youtube.com/watch?v=DYW50F42ss8
Three Types of Subatomic Particles
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Protons – Positive Charge (+1)
Neutrons – Neutral (no charge, 0)
Electrons – Negative Charge (-1)
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Locations
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Protons & Neutrons:
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Nucleus of Atom
Electrons:
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Found in the space outside the nucleus
Mass of Subatomic Particles
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When we measure the mass of protons, neutrons and
electrons, we consider RELATIVE masses
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That means we compare the mass of protons and neutrons
to the mass of electrons
Masses
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Proton = 1 amu (or Atomic Mass Units)
Neutron = 1 amu
Electron = 0 amu
What makes each atom different?
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John Dalton predicted that atoms of any element are
different from the atoms of all other elements
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Atoms of any given element always have the same
number of PROTONS
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Atoms of different elements have different numbers of
protons
Atomic Number
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Equals the number of protons in an atom
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Found on the Periodic Table of Elements
Number of Electrons
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Each positive charge in an atom is balanced by a
negative charge because atoms are neutral
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What does neutral mean?
The atomic numbers gives the number of protons AND
the number of electrons in a neutral atom of an
element
Practice
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How many protons does Sulfur have?
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How many electrons does Sulfur have?
Additional Practice
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On white boards
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How many protons does hydrogen have?
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How many electrons does oxygen have?
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How many protons does Magnesium have?
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How many electrons does Neon have?
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How many electrons does Lithium have?
Mass Number
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To find the number of neutrons in an atom, you have to
do some simple math…
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The mass number of an atom is the sum of the
number of protons and neutrons in an atom
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Protons have a mass of one, neutrons have a mass of one
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If we add them together we can find the total mass
Formula for Finding # of Neutrons
Number of Neutrons = Mass Number – Atomic Number
Practice
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A carbon atom has a mass number of 14
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How many protons does it have?
How many neutrons does it have?
Steps
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Look on the Periodic Table Elements to find the Atomic
Number of Carbon
Subtract the number of protons from the mass number. This
is the number of neutrons.
Finding Mass Number
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If an atom has 2 protons and 2 neutrons…
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What is the name of the element?
How many electrons does it have in a neutral atom?
What is the mass number?
If an atom has 11 protons and 12 neutrons…
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What is the name of the element?
How many electrons does it have in a neutral atom?
What is the mass number?
Isotopes
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Atoms of the same element that have different
numbers of neutrons, and, therefore, different mass
numbers
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For example
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How many protons does Oxygen have?
Sometimes Oxygen has 9 neutrons, sometimes it has 10
neutrons
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What is the mass number of an atom of oxygen that has 9 neutrons?
What is the mass number of an atom of oxygen that has 10 neutrons?
Identifying Isotopes
Element Name
Oxygen - 18
Mass Number
Practice
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Nitrogen – 14
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How many protons?
What is the mass number?
How many neutrons?
How many electrons?
Neon – 20
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How many protons?
What is the mass number?
How many neutrons?
How many electrons?
Modern Atomic Theory
4.3
Bohr Model
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Looks almost like a diagram of a solar system with
planets orbiting around the Sun
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Describes the arrangement of electrons in atoms
Energy Levels or Shells (Bohr Model)
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Electrons move in fixed orbits around the nucleus
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Each electron has a certain amount of energy that
determines the energy level that it is in
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Electrons can NOT exist between energy levels
Electron Cloud Model
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This model was an improvement on Bohr’s model
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Bohr assumed electrons moved like planets in a solar system,
but this is actually not the case
Electron Cloud
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Visual model of the most likely locations for electrons in an
atom
Describes the POSSIBLE locations of electrons around the
nucleus
At any moment in time we cannot pinpoint the location of an
electron
Atomic Orbitals
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A region of space around the nucleus where an
electron is most likely to be found
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Each energy level contains a certain number of atomic
orbitals
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Each orbital can contain a MAXIMUM of 2 electrons
Each Energy has a certain number of atomic orbitals
Energy Levels, Orbitals & Electrons
Energy Level
Number of Orbitals
Maximum Number
of Electrons
1
1
2
2
4
8
3
9
18
4
16
32
Creating a Model of an Atom
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We can use the energy level and atomic orbital
information in order to create a model of an atom
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Each energy level can contain a certain number of
electrons.
Steps for Making Models of
Atoms
Step 1
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Find the number of electrons in a neutral atom of the element
Step 2
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Draw concentric circles to represent the energy levels
Step 3
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Fill up the energy levels from the inside out with the
correct number of electrons.
REMEMBER: Only 2 electrons will fit in the first level (or
circle), 8 in the second, 18 in the third, etc.
Practice
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Create atomic models for the following elements:
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Helium
Argon
Magnesium
Carbon