Unit 2 Chemistry
Valance Electrons
Valence Electrons
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Valence electrons are the
electrons in the outer
energy level of an atom.
These are the electrons
that are transferred or
shared when atoms bond
together.
What does it mean to be
reactive?
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We will be describing elements according to their
reactivity.
Elements that are reactive bond easily with other elements
to make compounds.
Some elements are only found in nature bonded with
other elements.
What makes an element reactive?
 An incomplete valence electron level.
 All atoms (except H and He) want to have 8 electrons
in their very outermost energy level (This is called the
octet rule.)
 Atoms bond until this level is complete. Atoms with less
than 4 valence electrons lose them during bonding.
Atoms with 6, 7, or 8 valence electrons gain electrons
during bonding.
Elements that have either gained
or lost electrons are called ions.
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Positively charged: Cations
 Any atom that loses electrons to form
compounds are called cations. Cations
have a positive charge.
 Naming cations: Use the element name
followed by the word “ion”.
Table: Metal cations with more than one common charged form
Cation formula
Fe2+
systematic name
iron(II) ion
common name
ferrous ion
Fe3+
iron(III) ion
ferric ion
Cu1+
copper(I) ion
cuprous ion
Cu2+
copper(II) ion
cupric ion
Hg1+
mercury(I) ion
mercurous
ion
Hg2+
mercury(II) ion
mercuric ion
Pb2+
lead(II) ion
plumbous
ion
Pb4+
lead(IV) ion
plumbic ion
Sn2+
tin(II) ion
stannous ion
Sn4+
tin(IV) ion
stannic ion
Elements that have either gained
or lost electrons are called ions.
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Negatively charged: Anions
 Atoms that gain electrons to form
compounds are called anions. Anions
have a negative charge.
 Naming Anions: Drop the last few letters
of the element name and add “ide”.
Electron Orbitals
5
Bohr’s Model of the Atom
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Bohr Model
Electrons orbit the
nucleus at a fixed
distance.
Each orbit is associated
with a definite energy
level.
Energy levels are quantized
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Electrons travel in orbits
around the nucleus
The farther the electron
is from the nucleus the
more energy it has.
Bohr Diagrams
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These are simple diagrams that show the
number of electrons in each orbital of an
element.
The symbol of the element is placed in the
nucleus, and electrons are then placed in
each orbital.
Let’s do a couple of examples.- Si, N
Bohr-Rutherford Diagrams
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These diagrams are a combination
of a Bohr Diagram and a
Rutherford Diagram.
The main difference between this
diagram and the Bohr diagram is
the inclusion of the # of protons and
# of neutrons in the nucleus.
How To Draw Bohr-Rutherford
Diagrams:
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Draw the nucleus as a solid circle.
Put the number of protons (atomic number)
in the nucleus with the number of neutrons
(atomic mass – atomic number) under it.
Place the number of electrons (same as
protons) in orbits around the nucleus by
drawing circles around the nucleus.
Remember, 1st shell – 2 electrons, 2nd shell
– 8 electrons, 3rd shell – 8 electrons, 4th
shell – 18 electrons.
How To Draw Bohr-Rutherford
Diagrams:
Assignment
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Which Atom is Which
Intro. to chemistry