Transcript Chemical Bond - Cobb Learning

Chemistry
Chapter 11
Bonding
World of Chemistry
Zumdahl
Last revision Fall 2008
Bonding and Molecules

Reaction – When an atom interacts with
another atom forming a chemical bond.

Chemical Bond – An attraction between
two or more atoms that binds them
together.
Types of Chemical Bonds
Compounds are made from two or more atoms
that share a chemical bond.
1) Found only in definite ratios.
Examples: H2O, H2O2
2) They can be broken down in chemical
reactions.
There are two groups of compounds and types
of chemical bonds:
Ionic and Covalent
Why form chemical bonds?
1)Atoms tend to be stable when they have 8
electrons in their outer energy level.
Stable
Unlikely to react.
Unstable
Likely to react.
How do atoms become stable?
a) Those with 1 to 3 outer electrons tend to lose those
electrons because the next energy level in has 8 e-.
b) Those with 5 to 7 outer electrons tend to want to gain
extra electrons until they have 8 e-.
c) Those with 4 outer electrons tend to share those
electrons.
+3
-1
Can’t tell
-2
-3
Stable
+2
Valence number =
family number
share
+1
Ionic Bonds
This is the force of attraction between oppositely
charged ions.
a) Ion – an atom that gains or loses electrons.

Cation – positively charged ion = lost electrons

Anion – negatively charged ion = gained electrons
Chemical Formulas
Chemical Formula – This is the “recipe” of a compound.
It contains the ratios of the atoms combined in the
compound.
Sometimes information is given above the normal line of
information. In the example below, 12 and +4 are
written as what we call a superscript.
12 +4
C
6
1
Sometimes the information given is below the normal
line of information. In the example below, 6 and 1 are
written in subscripts.
Writing formulas for ionic compounds:
1)
2)

Write the symbol for the positive ion first
(determine the charge or oxidation number
using your periodic table)
Write the symbol for the negative ion second
(determine the charge or oxidation number
using your periodic table).
An oxidation number (or charge) indicates
how many electrons are lost, gained or shared
when bonding occurs.
Writing formulas for ionic compounds:
Add subscripts so that the sum of the
positive and negative oxidation numbers is
zero. The Crisscross Method or Swap N’
Drop Method can also work.
4) All compounds are neutral so the oxidation
numbers should combine in ratios that will
add up to zero. The number of ions
combining in the compound will be written
as subscripts in the final formula.
Example: Na+1 and Cl-1
(+1) + (-1) = 0
3)
NaCl

Try this example on your own:
Ca and Br
Ca+2
(+2)
Br -1
+
(-1) = +1
Add more negative
1
Ca+2 Br -1
Br -1
(+2)
+
CaBr 2
2
(-2) = 0
Swap and drop short cut
Al and O
Al+3
O-2
2
3
Al2O3
Charges can be
crisscrossed to
become subscripts
(remember to remove the sign)
Mg and Cl
Mg+2
Cl-1
1
MgCl2
2
A subscript of 1 is
never written.
The symbol
stands for 1.

Polyatomic Ions – Some covalently bonded
atoms function as a ion or charged particle.
Two important ones are hydroxide (OH-) and
ammonium (NH4+) Use parentheses to treat
the group as a single unit when writing the
chemical formula.
Example:
Al+3
1
OH-1
3
Al(OH)3
Whenever a
subscript is used to
indicate more than
one polyatomic ion
you must use
parenthesis
Naming Ionic Compounds:
1)
The first ion (cation or positive ion) keeps its
name. Example: NaCl Sodium
2) The second ion (anion or negative ion) keeps
the first syllable or the root of the name and
then ends in the suffix –ide.
Example: NaCl
Sodium chloride
3) If any of the ions are polyatomic, use the their
name from the list.
Transition Metals

Transition metals may occur in a variety
of oxidation states and a roman numeral
must be included in the name to tell the
reader which type of ion it is.

You should include a roman numeral for
all transition metals (except Silver [Ag+]
and Zinc [Zn+2]).
Fe+3 = Iron (III) Ion
Fe+2 = Iron (II) Ion
Transition Metals

There are two steps for determining the
charge on the transition metal.
1.
Un-crisscross the subscripts (remember:
no subscript indicates 1 atom)
2.
Check the anion (-) to see if you must
adjust the numbers
Example:
1. Un-crisscross
the charges.
+1
-1
FeO
+2 =2 x +1
2. Check the
anion.
-1 x 2= -2
FeO
Adjust as
needed.
The name for the compound is
Iron (II) Oxide
Naming Covalent Compounds:
1)
2)





4)
List the least electronegative first. First atom only
keeps it’s name and only uses a prefix if there is
more than one
List the most electronegative second. Second atom
ends with “ide” and always uses a prefix to tell how
many atoms of each there are:
mono = 1 atom
hexa = 6 atoms
di = 2 atoms
hepta = 7 atoms
tri = 3 atoms
octo = 8 atoms
tetra = 4 atoms
nono = 9 atoms
penta = 5 atoms
deca = 10 atoms
There are no charges in covalent compounds so there
is no crisscrossing or uncrisscrossing or roman
numerals.
Properties of Ionic compounds
– Ionic compounds are usually solids at room
temperature
Melting and Boiling Points
– Ionic compounds have much higher melting
points and boiling points than covalent
compounds
–– Ionic compounds typically melt at several
hundred degrees Celsius
•They exist in a crystal state so we refer to the smallest
ratio of ions in the crystal as their formula unit
•When dissolved in water, ionic compounds
break into ions (charged particles) and can
conduct electricity through the solution.
Properties of Covalent
compounds



Covalent compounds are typically formed
from nonmetals
Molecules – this is the single unit of
compounds characterized by covalent bonding
Exist as discrete molecules in the solid, liquid,
and gas states. They carry no charges.