Chemical Bonds
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Roughly 110 elements on the periodic table can
form a nearly infinite number of compounds
Elements bond with each other, seeking
stability
Only one group of elements (Noble Gases) are
stable without bonding
All others must bond with either another atom
of the same element or a different element to be
stable
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Elemental copper is a
shiny metal
The Statue of Liberty
is copper, why is she a
pale green color?
The copper that the
statue is made of
reacted with oxygen
and sulfur to form a
compound called
copper sulfate, that
has its own properties
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Sodium (Na) is a soft, silvery
metal that is highly reactive–
it actually catches fire in the
presence of oxygen
Chlorine (Cl) is a green
poisonous gas.
Together, they make a
compound that you can put
on your food, table salt, NaCl
Table salt’s compound name
is Sodium Chloride
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A chemical formula tells what elements are in a
compound, and in what numbers
Subscripts (a number written below) show how
many atoms are in each compound.
If there is no subscript, you can assume it is 1
Example, H2O, water, has two atoms of
Hydrogen and one atom of oxygen
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An atom is considered stable if its outer shell
electrons are full
This is considered an “Octet”, because 8
electrons fill the outer shell of some atoms
Outer shell electrons are called “valence”
electrons and are the electrons that are
involved in bonding
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Uses dots around
the chemical
symbol to show
number of valence
electrons
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Write the symbol of the element
Look at the periodic table and determine the
number of outer shell, or valence electrons
Start on the top, put one dot on each side as
you move clockwise
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Exceptions: He (helium) has a full shell at two
electrons, so put those dots on top
Group 1: Alkali metals (including H) put the one dot
to the right
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Atoms form chemical
bonds with each
other to reach
chemical stability– to
fill up their outer
shells
They will either give
away, take, or share
electrons to do this
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When atoms gain or lose an electron, they
become an ion
A positive ion, such as Ca +2, gives away 2
electrons
A negative ion, such as Chlorine -1, gains one
electron
A bond where electrons are transferred, (given
or taken) is called an IONIC bond
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Ionic bond is the force of attraction between
opposite charges in an ionic compound
For the most part, ionic bonds are formed by
elements that are far apart on the periodic table
A metal and a non-metal
Metals tend to lose electrons
Non-metals tend to gain electrons
Once ionic bonds are formed, the resulting
compound has a net charge of zero
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Non metals, when bonding with other non
metals, are unlikely to gain or lose electrons
The attraction that forms between atoms when
they share electrons is called a covalent bond
A neutral particle that forms due to a covalent
bond is called a molecule
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Single covalent bonds share one pair of
electrons, example is water H2O this is called a
single bond
A multiple covalent bond shares two or three
pairs of electrons, called a double or a triple
bond, example N2
Covalent bonds form between non-metals
Many covalent compounds are liquids or gases
at room temperature
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Polar covalent compounds are molecules that
have ends that have partial opposite charges
This means that the electrons are shared
unevenly
One atom has a greater “pull” on the shared
electrons than another
A non-polar compound mean that the electrons
are shared evenly with no partial charges
Water is Polar
Carbon Tetrachloride is
non-polar
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Some atoms are so reactant that they can’t exist
as only one atom
They must bond with themselves in order to
reach stability
They are called “diatomic” which literally
means “two atoms”
The diatomic atoms are: Nitrogen, Oxygen,
Fluorine, Chlorine, Iodine, Hydrogen, Bromine
Magic 7- they make a 7 and then add hydrogen
They are all written with a subscript: Cl2
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A binary ionic compound is one that consists of
two elements bonded together where electrons
are transferred
You need to know what elements are involved
and how many electrons are gained or lost
The element’s OXIDATION NUMBER tells
how many electrons are transferred when ions
are formed
Oxidation numbers are often referred to as
“charge”
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When compounds are
formed, their net
charge must be zero
Therefore, when you
are putting
compounds together
and writing their
formulas, their
oxidation numbers
must equal zero
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Sodium (Na +1) and
Chlorine (Cl -1)
together are NaCl
Magnesium (Mg +2)
and Chlorine (Cl -1)
together are MgCl2
It takes two chlorine
atoms to cancel out
the +2 charge of Mg to
zero
Criss-Cross method
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Step 1: Write the name of the positive ion
Step 2: Determine if the positive ion has a
special oxidation number (refer to table 2.) If it
does, you’ll have to determine its oxidation
number and write roman numerals after the
name
Step 3: Write the root of the negative ion
(chlor-, ox-, phosph-)
Add –ide to the end of the root of the negative
ion
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NaCl
Step one: Sodium
Step two: not needed, it only has one possible
oxidation number
Step three: Sodium ChlorStep four: Sodium Chloride
Now, you do MgI
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A polyatomic ion is a
special ion that is made of
many atoms
Look at the chart to the
right
To write the names of a
special compound with
polyatomic ion, you write
the name of the positive
ion and then the name of
the polyatomic ion
Ex K2SO4 is potassium
sulfate
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Naming covalent
compounds uses
prefixes that tell how
many of the atoms
are present in the
molecule
Often the prefix for
one, mono is omitted
but is used for
emphasis in some
cases
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CO is Carbon Monoxide
CCl4 is Carbon Tetrachloride
H2O is Dihydrogen Monoxide
Your Turn
NO2
N2O5