Transcript Chapter 4 The Structure of Matter How atoms form compounds Compounds      Formed when two or more elements combine Must make a chemical change New properties Atoms from.

Chapter 4
The Structure of Matter
How atoms form compounds
Compounds
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Formed when two or more elements
combine
Must make a chemical change
New properties
Atoms from the different elements form
bonds
Chemical Bond- the attractive force that
holds different atoms or ions together
Compounds
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Every compound has a specific ratio of
atoms
Written as a chemical formula
H2O, C12H22O12, NaCl
The ratio is the same every time, every
where
Different ratio means a different
compound
Chemical Structure
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Shows how the atoms are arranged in
the compound
How the atoms or ions are connected
In order to specify where we need
– Bond length- distance between the
nuclei
– Bond angle- Angle between atoms
(requires two bonds)
Models
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Ball and stick- Ball represents atoms,
stick represents bonds
Easy to see bond angles
Structural formulas- drawn with
connections between atoms shown.
H
O
H
H
H C
H
O H
Models
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Space-filling – Shows that atoms the
right size and in the right place.
C4H9O2N
2 Types of structures
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Networks
A large number of atoms, all bonded
together
Atoms bonded
Or ions opposite charges
Network Solids
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Many atoms all bonded together
Quartz is SiO2
Major component of rocks.
Each Silicon bonded to 4 oxygen atoms
Angle is 109.5º
Gives it a strong rigid
structure
Makes rocks hard.
Gives them a high
melting and boiling point
Network Solids
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Ions bond together
Opposite charges attract
All the positives get
surrounded by negatives
Get a repeating
pattern
Rigid
Brittle
High mp and bp
Molecules
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Specific atoms joined together
Weaker attractions than ions.
Low melting and boiling points
Things we know as gases and liquids
Stronger attraction- higher melting and
boiling temperatures
Bonding
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When the valence electrons interact
Atoms react to achieve full outermost
energy levels
Two ways to do this
– Share electrons
– Transfer electrons
Keeping Track of Electrons
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Atoms in the same column
Have the same outer electron
configuration.
Have the same valence electrons.
Group 1 has 1 valence electrons
Group 2 has 2 valence electrons
Group 13 has 3 valence electrons
Group 14 has 4 valence electrons
etc
12
Helium only has 2
valence electrons
8
3 4 5 67
Electron Dot diagrams
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A way of keeping track of
valence electrons.
How to write them
Write the symbol.
Put one dot for each
valence electron
Don’t pair up until they
have to
X
The Electron Dot diagram
for Nitrogen
Nitrogen has 5 valence
electrons.
 First we write the symbol.
Then add 1 electron at a
time to each side.
Until they are forced to pair up.
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N
Write the electron dot diagram
for
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Na
Mg
C
O
F
Ne
He
Electron Configurations for
Cations
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Metals lose electrons to fill their outer
levels
They make positive ions.
Electron Dots For Cations
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Metals will have few valence electrons
Ca
Electron Dots For Cations
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Metals will have few valence electrons
These will come off
Ca
Electron Dots For Cations
Metals
will have few valence electrons
These will come off
Forming positive ions
+2
Ca
Electron Configurations for
Anions
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Nonmetals gain electrons to fill their
outer levels
They make negative ions.
Electron Dots For Anions
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Nonmetals will have many valence
.electrons.
They will gain electrons to fill outer shell.
P
-3
P
Stable Arrangements
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All atoms react to fill their outer levels
Noble gases have full outer energy
levels.
8 valence electrons .
Also called the octet rule.
Ar
Ionic Bonding
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Anions and cations are held together by
opposite charges.
The bond is formed through the
transfer of electrons.
Electrons are transferred to fill their
outer levels
Ionic Bonding
Na Cl
Ionic Bonding
+
Na
Cl
-
Ionic Bonding
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All the electrons must be accounted for!
Ca
P
Ionic Bonding
Ca
P
Ionic Bonding
+2
Ca
P
Ionic Bonding
+2
Ca
Ca
P
Ionic Bonding
+2
Ca
Ca
P
-3
Ionic Bonding
+2
Ca
P
Ca
P
-3
Ionic Bonding
+2
Ca
P
+2
Ca
P
-3
Ionic Bonding
Ca
+2
Ca
P
+2
Ca
P
-3
Ionic Bonding
Ca
+2
Ca
P
+2
Ca
P
-3
Ionic Bonding
+2
Ca
+2
Ca
+2
Ca
P
P
-3
-3
Ionic Bonding
Ca3P2
Formula Unit
Properties of Ionic Compounds
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Crystalline structure.
A regular repeating arrangement of ions
in the solid.
Ions are strongly bonded.
Structure is rigid.
High melting points- because of strong
forces between ions.
Crystalline structure
Do they Conduct?
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Conducting electricity is allowing charges
to move.
In a solid, the ions are locked in place.
Ionic solids are insulators.
When melted, the ions can move around.
Melted ionic compounds conduct.
First get them to 800ºC.
Dissolved in water they conduct.
Metallic Bonds
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How atoms are held together in the
solid metal
Metals hold onto there valence
electrons very weakly.
Think of them as positive ions floating
in a sea of electrons.
Sea of Electrons
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Electrons are free to move through the
solid.
Metals conduct electricity.
+
+ + +
+ + + +
+ + + +
Metals are Malleable
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Hammered into shape (bend).
Ductile - drawn into wires.
Malleable
+
+ + +
+ + + +
+ + + +
Malleable
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Electrons allow atoms to slide by.
+ + + +
+ + + +
+ + + +
Ionic solids are brittle
+
+
-
+
+
+
+
-
+
+
Ionic solids are brittle
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Strong Repulsion breaks crystal apart.
- + - +
+ - + - + - +
Covalent bonds
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Nonmetals hold onto their valence
electrons.
They can’t give away electrons to bond.
Still want full outer level
Get it by sharing valence electrons with
each other.
By sharing both atoms get to count the
electrons toward noble gas
configuration.
Covalent bonding
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Fluorine has seven valence electrons
F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
F
F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
F
F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
F
F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
F F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
F F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
F F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
Both end up with full energy level
F F
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
Both end up with full energy level
F F
8 Valence
electrons
Covalent bonding
Fluorine
has seven valence electrons
A second atom also has seven
By sharing electrons
Both end up with full energy level
8 Valence
electrons
F F
Single Covalent Bond
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A sharing of two valence electrons.
Only nonmetals and Hydrogen.
Different from an ionic bond because
they actually form molecules.
Two specific atoms are joined.
In an ionic solid you can’t tell which
atom the electrons moved from or to.
How to show how they formed
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It’s like a jigsaw puzzle.
I have to tell you what the final formula
is.
You put the pieces together to end up
with the right formula.
For example- show how water is formed
with covalent bonds.
Water
H
O
Each hydrogen has 1 valence
electron
Each hydrogen wants 1 more
The oxygen has 6 valence
electrons
The oxygen wants 2 more
They share to make each other
happy
Water
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Put the pieces together
The first hydrogen is happy
The oxygen still wants one more
HO
Water
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The second hydrogen attaches
Every atom has full energy levels
HO
H
Multiple Bonds
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Sometimes atoms share more than one
pair of valence electrons.
A double bond is when atoms share two
pair (4) of electrons.
A triple bond is when atoms share three
pair (6) of electrons.
Carbon dioxide
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C
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O
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CO2 - Carbon is central
atom ( I have to tell you)
Carbon has 4 valence
electrons
Wants 4 more
Oxygen has 6 valence
electrons
Wants 2 more
Carbon dioxide
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Attaching 1 oxygen leaves the oxygen 1
short and the carbon 3 short
CO
Carbon dioxide
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Attaching the second oxygen leaves
both oxygen 1 short and the carbon 2
short
OC O
Carbon dioxide
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The only solution is to share more
O CO
Carbon dioxide
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The only solution is to share more
O CO
Carbon dioxide
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The only solution is to share more
O CO
Carbon dioxide
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The only solution is to share more
O C O
Carbon dioxide
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The only solution is to share more
O C O
Carbon dioxide
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The only solution is to share more
O C O
Carbon dioxide
The only solution is to share more
 Requires two double bonds
 Each atom gets to count all the atoms in
the bond
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O C O
Carbon dioxide
The only solution is to share more
 Requires two double bonds
 Each atom gets to count all the atoms in
the bond
8 valence
electrons
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O C O
Carbon dioxide
The only solution is to share more
 Requires two double bonds
 Each atom gets to count all the atoms in
the bond
8 valence
electrons
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O C O
Carbon dioxide
The only solution is to share more
 Requires two double bonds
 Each atom gets to count all the atoms in
the bond
8 valence
electrons
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O C O
Another way of indicating
bonds
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Often use a line to indicate a bond
Called a structural formula
Each line is 2 valence electrons
H O H =H O H
Structural Examples
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H C N
H
C O
H
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C has 8 electrons
because each line
is 2 electrons
Ditto for N
Ditto for C here
Ditto for O