Transcript Chapter 4 The structure of matter

Chapter 4
The structure of matter
What are compounds?
When two or more elements combine
to form something that has properties
very different from those of the
elements that make it up.
Always represented by a chemical formula:
which means that they are always made of the
same elements in the same proportions
Held together by chemical bonds
What is the difference between a
compound and a mixture
Mixture are made of different substances
that are just placed together…compounds
result from a chemical reaction where new
bonds are formed
Mixtures don’t have a chemical formula and
are not always in the same proportion while
compounds always are made of the same
elements in the same proportions
Models of compounds
Ball and stick
Balls: show atoms
Space filling
models
Shows the space
that is occupied
Sticks: represent bonds
by the atoms
Ex: ferrocene
If the same elements are present in 2
compounds, are the compounds the same?
NO, the same elements can be present
in both compounds but form different
compounds because the amount of
each element is different or the
orientation of the elements is different
Example: both carbon dioxide CO2 and
Carbon monoxide CO have carbon and
oxygen
Also Water H2O and hydrogen peroxide
H2O2 have hydrogen and oxygen
Why do atoms sometimes join to
form compounds?
•To make their outermost
energy level full
•The outer energy level max
capacity is 8 electrons.
There are 2 types of bonds that form for
compounds
Characteristics of Ionic bonds
, Formed between oppositely charged ions
One atom will gain electrons and the other atom
will lose electrons
Metals form the positively charged ions (cation)
Nonmetals form the negatively charged ion
(anion)
Form networks not molecules so don’t call them
molecules but talk about ratio of ions
The compound has a total charge of zero
When melted or dissolved ionic compounds
conduct electricity
Continue with ionic characteristics
All ionic compounds form
crystals
Ionic compounds tend to have
high melting and boiling points.
Ionic compounds are very hard
and very brittle
Characteristics of Covalent bonds
Made of molecules
Bond between nonmetal atoms
Low melting point
Do not conduct electricity because are not
charged
Joined by sharing electrons
If share electrons equally then : nonpolar
covalent bonds
If share electrons unequally and electrons
are attracted to one atom more than
another: polar covalent bonds (electrons are
attracted to elements located farther right
and top)
Compounds that have both Covalent and
Ionic bonds
• Made of polyatomic ions, which
are covalently bonded atoms that
have either lost or gained
electrons
Parentheses group the atoms of a
polyatomic ion (NH4)SO4
Determine if the following compounds
are ionic or covalent bonds
1. Magnesium oxide, MgO
2. Ozone, O3
3. Strontium chloride, SrCl2
4. Methanol CH4O
5. Sugar C12H22O11
6. Potassium hydroxide, KOH
7. Dinitrogen tetroxide N2O4
Rules for naming ionic compounds
1. Most ionic compounds (and any I
would ever give on a test) have two
word names. The first word in the
namecation, and the second word is
the name of the anion. There is no
exception to this rule.
2. The best way to go about naming ionic
compounds is to take a look at the
formula and figure out the names of
the cation and anion. When you've got
that, just stick them together and
you've got the name of the compound.
Handy method for naming ionic compounds
if you are given the chemical formula
Let's go through this using an
example: Fe2(SO4)3
1. Step One: Name the cation and anion
In this case, you should recognize
that Fe is "iron", and that SO4 is
the "sulfate" ion.
Step Two: Figure out if you need
a Roman numeral in the name.
IF the cation in the compound you're naming is
not a transition metal, then you definitely
don't need to use a Roman numeral and the
naming is done.
If there is, then you need to figure out whether
or not the cation can exist in more than one
charge. If not, then you don't need a Roman
numeral. If so, then move on to Step Three...
Step Three: Figure out what the
Roman numeral should be
A good rule of thumb is that usually the number of
anions you have in the molecule is equal to the
charge on the cation, and that the number of
cations you have is equal to the number of
anions.
Using our example, there are three sulfate ions,
meaning that iron has a charge of +3. Likewise,
since there are two iron atoms, the sulfate has a
charge of -2. Since iron has a charge of +3 in
this compound,
the name in this example is iron (III) sulfate.
Step Four: Check your work
1. Look at the answer from the last step,
and ask yourself whether the charges
are OK. Is +3 a charge that iron can
have?
2. Is -2 the charge of the sulfate ion?
3. In this case, the answer to both
questions is "yes",
4. so we're finished, and the answer of iron
(III) sulfate stands.
But... what if we find a mistake when we
check our work?
this case, you have to find another way to
solve the problem. Take the example of FeS.
If we solve the problem using the first three
steps, we find that the formula should be
iron (I) sulfide. However, if we check this
work as we should in step four, we find that
iron cannot have a charge of +1, only +2 or
+3, and sulfur can only have a charge of -2.
In a case like this, you need to find
another way to solve the problem.
When this happens, look at the anion. In
our example of FeS, the anion is the
sulfide anion, S-2. If we have one sulfide
ion, this means that the total negative
charge in the molecule is -2. As a result,
iron must have a charge of +2 to
counterbalance the -2 charge of sulfur.
Since iron has a charge of +2, the name
of the compound is
iron (II) sulfide.
Handy method if giving the
formula if given the name
• We'll use an example to find the formula of an
ionic compound: copper (II) fluoride
Step One: Translate the name into the
ions
copper (II) fluoride, the cation is the copper (II)
ion and the anion is the fluoride ion.
Hopefully, you realize that the copper (II) ion is
simply Cu2+ and the fluoride ion is F-. If not,
then you need to go back and review the
rules for naming ions above.
Step Two: Put brackets around
the ions, but leave the charges
on the outside.
In this case, the copper (II)
ion would be [Cu]2+ and
the fluoride ion would be [F]1.
Never change anything in
these brackets, ever!
Step Three: Put the ions next
to each other.
When we do
this here, we
get
2+
1
[Cu]
[F]-
Step Four: Cross the charges:
The charge on the cation will be equal
to the number of anions you have,
and the charge on the anion will be
equal to the number of cations you
have.
In our example, you should realize
that we have one copper atom
(because the charge on fluorine is -1)
and two fluoride ions (because the
charge on copper is +2).
This gives us a formula of: [Cu][F]2
Step Five: Take the brackets
away.
The final formula
for copper (II)
fluoride is then
CuF2
Exceptions:
1. IF the charges on the ions can be
divided by the same number, then
do it before you do step four. For
example, if you were to find the
formula for manganese (IV) oxide,
you'd realize in step three that
both manganese (IV) and oxygen
have charges that can be divided
by two.
Step 2
Instead of crossing the +4 for
manganese and the -2 for
oxygen, you'd simplify it so that
you cross a +2 for manganese
and a -1 for oxygen
Step 3
1. IF we have a polyatomic ion, such as
sulfate or ammonium, you need to
replace the brackets with parentheses
in step five. For example, if you end
up with [NH4]2O as the formula for
ammonium oxide at the end of step
four, you'd simply replace the
brackets with parentheses in step five
to give you (NH4)2
Rules for binary covalent
compounds
Rule 1. The element with the
lower group number is written
first in the name; the element
with the higher group number is
written second in the name.
Exception: when the compound
contains oxygen and a halogen,
the name of the halogen is the
first word in the name.
Rule 2. If both elements are
in the same group, the
element with the higher
period number is written
first in
the name
Rule 3. The second element in
the name is named as if it
were an anion, i.e., by adding
the suffix -ide to the
name of the element.
Rule 4. Greek prefixes (see the Table
provided at the bottom of this page)
are used to indicate the number of
atoms of each nonmetal
element in the chemical formula for
the compound.
Exception: if the compound
contains one atom of the
element that is written first in
the name, the prefix "mono-" is
not used.
Prefixes for covalent bonds
Number of atoms
1
2
3
4
5
6
7
8
9
10
prefixes
Mono
Di
Tri
Tetra
Penta
HexaHepta
Octa
Nona
Deca
Oxidation numbers of some polyatomic ions
+1
Ammonia NH4
-1
Acetate
CH3Coo
+4
Lead IV
Pb
+2
Mercury I Hg2
-1
Bromide Br
Chloride Cl
Fluoride F
Hydride H
Iodide I
-2
Oxide O
Sulfide S
Oxidation numbers of some monatomic ions
+1
Hydrogen H+
Lithium Li+
Potassium K+
Silver Ag+
Sodium Na+
+3
Aluminum Al
Chromium III
Cr
Iron III Fe
+4
Lead IV
Pb
+2
Barium Ba MagnesiumMg
Cadmium Cd Magnanese II Mn
Calcium Ca MercuryII Hg
Cobalt II Co NickelII Ni
Copper Cu
Strontium Sr
Iron II Fe
Tin II Sn
Lead II Pb
Zinc Zn
-1
Bromide Br
Chloride Cl
Fluoride F
Hydride H
Iodide I
-2
Oxide O
Sulfide S