CHEM
IS
FUN
REGENTS REVIEW,MAY 31, JUNE 1,2 2008
CAIAFA
DRAW THE DOT STRUCTURES OF H
2
,O
2
,N
2
,Cl
2
,Br
2
,I
2,
F
2
.
1)
How would you estimate the relative melting and boiling points of these?
2)
Put them in ascending boiling point order and indicate how you do this.
3)
Indicate the type of molecule and type of bond.
4)
List the characteristics and explain them with the bonding and type of attraction.
THIS H SHARES THE 2
ELECTRONS IT NEEDS, H IS
NOT AN OCTET ELEMENT
H H STEP 1 H H
THIS H SHARES THE 2
ELECTRONS IT NEEDS, IT NOW
HAS THE CONFIGURATIONOF
He
:
STEP 2
H H = H
2
D.
THE IONIC
CHARACTER
IS 0.0, THE
BOND IS
NON-POLAR
COVALENT
DRAW LEWIS
VALENCE DOT
STRUCTURE,
CONNECT ONLY
SINGLE
ELECTRONS
DRAW LEWIS
VALENCE DOT
STRUCTURE,
EACH SINGLE
BOND IS 2 e-
DRAW LEWIS
VALENCE DOT
STRUCTURE,
EACH
ELECTRON
PAIR IS A DASH-
LINE!

1) Gives geometry to assess polarity etc.
2) Assume central atom is LEAST electronegative.
3) Hydrogen cannot be the central atom as it makes only one bond.
UNBONDED e-
PAIRS ON
CENTRAL ATOM
0
1
2
NO CENTRAL,
ONLY 2 ATOMS
0
BONDS ON
CENTRAL ATOM
GEOMETRY
4 TETRAHEDRAL
3 PYRAMIDAL
2 BENT
(V SHAPE)
1(in molecule) LINEAR
3 TRIGONAL
PLANAR
EXAMPLES
C
2
N
B
O
2
3
4
3

O O STEP 1
O O
STEP
2
O O
D.
O
2
DRAW LEWIS VALENCE
DOT STRUCTURE,
CONNECT ONLY SINGLE
ELECTRONS, 2 FOR EACH
OXYGEN
EACH O SHARES THE 4 e-(DOUBLE
BOND) ELECTRONS IT NEEDS, IT
NOW HAS THE OCTET
CONFIGURATION OF NEON
Ne
Important: ALL OF THIS SERIES (
H
2
,O
2
,N
2
,Cl
2
,Br
2
,I
2
,F
2
)
A RE NON POLAR FOR THE FOLLOWING REASONS:
1) THEY HAVE IONIC CHARACTER OF 0.0
2) THEY ARE LINEAR (SYMMETRICAL) – ONE BOND
3) THE BONDS ARE NON POLAR.
4) ALL (EXCEPT I AND Br) ARE GASSES AT STP.
5) ALL ARE ELEMENTAL MOLECULAES, OXIDATION STATE 0!

N N STEP 1 N N STEP 2 N N
The electron configuration of nonmetals will resemble the noble gas of their own period
Connect only single electrons for covalent
(molecular) substances.
Each nitrogen has an octet, isoelectronic to
Each nitrogen shares 6 electrons, triple bond.
Ne
RELATIVE ASCENDING BOILING AND MELTING SERIES
H
2
(2g/mol) , O
2
(32), N
2
(28), Cl
2
(70), Br
2
(161), I
2
(254 ), F
2
(38)
Solid at
Liquid
STP at STP
H
2
(2g/mol) , N
2
(28), O
2
(32), F
2
(38), Cl
2
(70), Br
2
(161), I
2
(254 )
1-LOWEST 5 6 7-HIGHEST 2 3 4
Van der Waals increase with molar mass (gfm), use gfm for nonpolar

DRAW THE DOT STRUCTURES FOR H
2
CH
4
, HF.
a.
WHICH AR POLAR, WHICH ARE NOT.
O, H
2
S, SiO
2
, CO
2
, CCl
3
F, b.
-
INDICATE THE TYPE OF BOND AND THE TYPE OF MOLECULE FOR
EACH.
c.
-
PUT IN ASCENDING BOILING POINTS, INDICATE HOW YOU SO
THIS.
d.
-
List the characteristics of each and explain why.
IONIC CHARACTER
= 2.1 – 3.5 = 1.4 , POLAR COV.
H O H STEP 1
H O H
STEP 2
H
O H
Connect single electrons
Each H shares the 2 eachieve He : configuration
O shares the 8 e- achieve Ne configuration
Ne
Next slide

H O H
WITH 2 BONDS AND 2 UNSHARED PAIRS
OF e-, THE GEOMETRY IS BENT.
THE BONDING IS
CORRECT, BUT THE
GEOMETRY IS NOT!
H
O
H
YELLOW ARROWS ARE BOND POLARITY
VECTORS, PONT TO MOST ELECTRONEGATIVE
ELEMENT, NEGATIVE POLE.
+ +
THE LEAST
ELECTRONEGATIVE ATOM IS
THE POSITIVE POLE AND GETS
THIS POSITIVE POLE SYMBOL
+
THE MOST ELECTRONEGATIVE
H
ATOM IS THE NEGATIVE POLE
AND GETE THIS NEGATIVE
POLE SYMBOL
-
O
H
-
THE 2 YELLOW VECTOR
ARROWS ADD UP TO THIS
BIG ONE , WHICH
REPRESENTS MOLECULAR
POLARITY, POINTS TO
NEGATIVE POLE.

+
H
O
H
-
+
AS IONIC
CHARACTER
INCREASES causes
+
H
S
H
+
-
IONIC CHARACTER(EACH BOND)
=| 2.1 – 2.6| = 0.5 , WEAKLY POLAR
COVALENT.
+ =
BOND
POLARITY
INCREASES causes
MOLECULAR
POLARITY
INCREASES
(
IF ASSYMETRICAL)
H
2
O HAS
GREATER IONIC
CARACTER
THAN H
2
S causes
H
2
O HAS
GREATER
BOND
POLARITY
THAN H
2
S causes
WATER IS
MORE POLAR
HAS HIGHER
MELTING AND
BOILING POINTS

Si O
STEP 1 d O Si O
O
Note: THE Si IS HYBRID, NOT
GROUND STATE.
SI
Si
EACH OXYGEN HAS
SHARED 4 e- TO
ACHIEVE AN OCTET
IONIC CHARACTER
= |3.5 – 1.9| = 1.6, STRONGLY POLAR COV.
EACH THE Si HAS
SHARED 4 e- TO
ACHIEVE AN OCTET
O Si O
SiO
2
(silicon dioxide) is NONPOLAR , it is LINEAR ( 2 bonds) and symmetrical. The BONDS ARE polar but the molecule is not!
NOTICE THE VECTOR ARROWS CANCEL = 0

IONIC CHARACTER(EACH BOND)
=| 2.1 – 2.6| = 0.5 , WEAKLY POLAR
COV.
O C O
CO
2
(carbon dioxide) is NONPOLAR , it is LINEAR
( 2 bonds) and symmetrical. The BONDS ARE polar but the molecule is not! = 0.0
NOTICE THE VECTOR ARROWS CANCEL
H
H
Note: THE C IS HYBRID, NOT
GROUND STATE.
C
C H
+
+
H
H C F
H
POLAR BONDS,
SYMMETRICAL
NON POLAR MOLLECULE
H
+
-
POLAR BONDS,
A-SYMMETRICAL POLAR
MOLLECULE

IONIC CHARACTER
= |1.3 – 3.2| = 1.9 , IONIC
Mg +
Mg IS AN ACTIVE
METAL THAT
NEEDS TO LOSE 2 e-
Note: Mg+ 2 has a Ne electron configuration.
Cl
Mg +2
STEP 1
Cl
The electron configuration of metals will resemble the noble gas of the period before the period of the metal [
Cl IS AN ACTIVE
[
Cl
Cl
NON-METAL THAT
NEEDS TO GAIN 1 e-
[
Note: Cl- has an Ar electron configuration.
-
Mg 2+ Cl 1MgCl
2

Al 3+ F 1AlF
3
CHARACTERISTICS OF IONIC SOLIDS
1) Form crystal lattice solid with very strong electrostatic attractions between ions.
2) Ions are fixed in place, rendering the crystal non-conductive, brittle and hard .
3) The electrons cannot leave the ions, cannot conduct.
4) The strong electrostatic attractions make it difficult to separate the ions, and this requires great amounts of energy, thus the melting and boiling points are very high.
CHARACTERISTICS OF IONIC liquids and solutions (aq)
1) Soluble ionic compounds (table F) form conductive solutions mobile ions.
2) The melt of an ionic substance is always conductive.
3) Remember: FOR CONDUCTIVITY – MUST HAVE MOBILITY! (OF IONS
OR ELECTRONS)

O C O
EACH OXYGEN HAS
2 SINGLE
ELECTRONS, NEEDS
TO SHARE TWO
MORE FOR AN
OCTET, AND TO
RESEMBLE NEON.
EACH HYBRID CARBON HAS 4 SINGLE ELECTRONS,
NEEDS TO SHARE FOUR MORE FOR AN OCTET, AND
TO RESEMBLE NEON.

O C O
THE YELLOW CIRCLE
REPRESENTS THE
OXYGEN”SET” WITH
AN OCTET
THE BLUE CIRCLE
REPRESENTS THE
CARBON”SET” WITH
AN OCTET
THE GREEN
INTERSECTION AREAS
REPRESENT THE 4
SHARED ELECTRONS
OF A DOUBLE BOND

O C O
CO
2
HAS AN IONIC
CHARACTER OF 0.9,
WHICH IS CONALENT
POLAR
EACH DOUBLE BOND
IS 4 SHARED
ELECTRONS, IS
SHORTER AND
STRONGER THAN
THE SINGLE BOND.
AS WIH ALL COVALENT
COMPOUNDS, CO
2
HAS
WEAK ATTRACTIONS,
LOW M.P. AND B.P.AND
IS NEVER CONDUCTIVE.

•
Covalent bonds are formed by sharing at least one pair of electrons.
• Every covalent bond has a characteristic length that leads to maximum stability.
– This is the bond length .