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Compounds
•Elements will bond with other elements to
form compounds. Eg: MgCl2
•There are two types of bonds:
Ionic: Valence electrons are transferred
Covalent: Valence electrons are shared
•The reason for bonding is to achieve a
STABLE NUMBER of Electrons in the
VALENCE shell.
IONIC COMPOUNDS
A GIVE AND TAKE RELATIONSHIP
IONIC COMPOUNDS
•One atom (METAL) loses electron(s) so it is
overall positively charged ion
Cation
•One atom (NON-METAL) gains electron(s) so it
becomes negatively charged ion Anion
The electron(s) will be transferred from the
metal to the non-metal.
Making Ionic Compounds
• Ionic compounds are made
when large numbers of
sodium and chloride ions
join together to form an ionic
crystal. An example is NaCl,
sodium chloride.
• Looking at one NaCl particle,
we see that the ionic bond
between the sodium cation
and the chloride anion is
formed by the transfer of an
electron from the metal to
the non-metal.
5.6
Properties of Ionic Compounds
5.6
• Ionic bonds are very strong, resulting
in the following physical properties:
• Hard
• Brittle
• High melting points (most are
solids at room temperature)
• Conductivity of electricity (when
melted or dissolved in water)
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Properties of Ionic Compounds
• Most ionic
compounds are
soluble in water.
• When ionic
compounds dissolve,
they break apart into
their ions and
produce a solution
that conducts
electricity. Such
solutions are known
as electrolytes.
IONS & THEIR CHARGES
•How do we know what charge an ion will
form? LOOK AT YOUR PERIODIC TABLE !!
•Groups 1, 2, and 3 (13) will lose electrons,
and have charges of 1+, 2+, and 3+,
respectively.
•Groups 5 (15), 6 (16), and 7 (17) will gain
electrons, and have charges of 3-, 2-, and 1-,
respectively.
Practice:
What charges will these ions form?
• Litium [Li]
• Li +
• Fluorine [F]
• F• Boron [B]
• B 3+
• Sulfur [S]
• S 2-
5.6
• Phosphorous [P]
• P 3• Barium [Ba]
• Ba 2+
• Iodine [I]
• I• Xenon [Xe]
• Gotcha !
The Compound is called…
NAMING IONS
•The CATION (+ve ion) is usually the METAL
and its name stays the same as the element.
•Ex. Ca and Ca2+ are still called Calcium,
where Ca2+ is a calcium ion.
•The ANION (-ve ion) is usually the NONMETAL and its name ending will change to
“ide”.
•Ex. Br- is called Bromide ion.
Ionic compounds that gain or lose
the same number of electrons
automatically combine in 1:1 ratios
•Calcium bromide
•The chemical formula for calcium
bromide is…
CaBr2
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WHAT IF WE WERE FORMING
IONIC COMPOUNDS WITH IONS
WHOSE CHARGES DIDN’T ADD
UP TO A CHARGE OF EXACTLY 0?
WE HAVE A TRICK THAT WILL
HELP US KNOW THE NUMBER
OF THE IONS TO MAKE A
NEUTRAL COMPOUND.
HOW DO WE DECIDE
THE RATIO OF THE
IONS?
IT’S NOT A TRICK SO MUCH
AS A SHORTCUT!
CRISS-CROSS RULE:
Step 1: Write the symbols for each
element in the compound (metal
element first).
CRISS-CROSS RULE:
Step 2: Write the ionic charge as a
superscript above each symbol.
(eg. Al 3+)
.
Ca P
CRISS-CROSS RULE:
Step 3: Criss-cross the numerals of
the ionic charges and drop them as a
subscript to determine the number of
each element needed to balance the
ionic charges.
2+ 3-
Ca P
2+
Ca P
3-
CRISS-CROSS RULE:
Step 4: Write the formula using
subscripts for each element.
Ca 3 P 2
Calcium Phosphide
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CRISS-CROSS RULE notes:
CRISS-CROSS RULE:
•The subscript ‘one’ can be dropped.
•If both elements have the same
subscript, the numbers can be dropped.
•Subscripts must be reduced to lowest
terms since the subscripts indicate the
smallest whole number ratio of elements
in the compound.
Let’s try some…
Write the full chemical equation for the following
reactions and name the ionic compound
•Li + Cl
•Mg + Cl
HOMEWORK
•Pg 191 #1-3, 5
•Pg 195: #1-3, 5, 7, 13
•Pg 200: #2 and 3
•Worksheets
•Al + O
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