How Electrons Determine
Chemical Behavior
Day 3
Curriculum
Big Idea: Chemical bonding occurs as a result of
attractive forces between particles.
 Concept #1: Electrons are found in quantized
energy levels within the atom.
 Concept #2: The electronic structure within atoms is
predicted by the Aufbau Principle, the Pauli
Exclusion Principle, and Hund’s Rule, giving the
atom its most stable arrangement.
PA Standard: 3.2.C.A2 “Compare the electron

configurations for the first twenty elements of
the periodic table.”
Agenda
Opener: How many more electrons does potassium have than
Argon? How many less electrons does Oxygen have than Neon?
 Finish Activity 7: Go over the Investigation and the Chemistry to
Go
 Preview for Thursday and Friday: Ms. Dinger will be presenting
research at the National Science Teachers’ Association
Conference. Take a look at what you will be working on in class
Thursday and Friday. Take notes on subatomic particles and
atomic structure.
 Closure: What is the sublevel to which the last electron is
assigned for Magnesium? How many electrons are in this
sublevel (Big number, letter, superscript)
Take Home Assignement: Read section 4.3 in the Big Red Book

Atom:
the smallest particle of an element
that retains its identity in a chemical
reaction
Today’s Chemistry Word:
The Atomic Nucleus
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Core of the atom
Small
Dense
Positively charged
Composed of protons (+) and neutrons (0)
Atomic Number
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The whole numbers in the blocks of the
periodic table
The number of protons in one atom of a given
element
The number of electrons in a NEUTRAL atom
of a given element
Every element has a different number of
protons.
Mass Number
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The total number of protons and neutrons in
an atom of a given element
Round the atomic masses on the periodic
table.
# neutrons = mass number – atomic number
Protons, Neutrons, Electrons
Isotopes of an Element
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have different numbers of neutrons, so they
have different masses.
Example:
neon-20, neon-21, and neon-22 are three isotopes
of neon, a gaseous element used in lighted signs.
Isotopes of Hydrogen
Isotopes of Hydrogen
also called…
Hydrogen-1
Hydrogen-2
Hydrogen-3
Atomic Mass
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atomic mass unit (amu): one twelfth of the
mass of a carbon-12 atom.
Example: helium-4 has about one-third the
mass of a carbon-12 atom
Example: nickel-60 has about five times the
mass of a carbon-12 atom.