CH 4: Formation of
Compounds
Compounds
ž
Atoms of more than one element
chemically bonded
ž
Properties of compound unlike
properties of the individual elements
Compounds
Contain atoms of more than one
element
ž Properties of the compound do not
resemble the properties of the individual
elements
ž
› Example: Na + Cl à NaCl
Octet Rule
•
Elements gain/lose, or share e- to get 8
valence e- (Noble gas configuration)
•
2 ways to get a full octet
1. e- transfer
2. e- sharing
Octet Rule
•
•
e- transfer
Electron Transfer
ž
IONIC COMPOUNDS are Composed of:
› Usually a metal (positive ion) with
› a nonmetal (negative ion)
ž
Opposites attract (+ àß -) to form an
Ionic bond
ž
Charges must add up to zero
› (no net charge)
Show [Na]+ + [Cl]- (cl has 8 dots, one dot is different to show that it came from Na)
Binary Ionic Compounds
ž “Binary”
ž Mg
= 2 elements
& Cl
› Combine so that charges = 0
› MgCl2
ž K
&O
ž Pb4+
&S
ž Fe2+ &
O
Ionic Compounds
› Crystalline solids
› High melting points
› Solids at room temp.
› Conduct electricity when melted &
when dissolved
– not in solid state
ž
Formula unit: smallest ratio of ions to make a
neutral ionic compound
Electron Sharing
ž Occurs
when neither atom attracts e-
strongly
ž 2
ž
nonmetals
Covalent Bonds
ž All
atoms in a molecule must have a full
octet
› 8 e-
– except H (2 e-)
Single bond
Octet Rule
Covalent Compounds
ž
Covalent bond: attraction of 2 atoms for
a shared pair(s) of e› both atoms stay neutral
ž
Molecule: smallest unit of a covalent
compound
ž
Can share 1, 2, or 3 pairs of e-
Ionic or Covalent Compound?
ž Methane
– CH4
covalent
ž Potassium
Chloride – KCl ionic
ž Iron (II) oxide – FeO ionic
ž Carbon Monoxide – CO covalent
ž Carbon disulfide – CS2
covalent
ž Calcium
Chloride – CaCl2
ionic
Ionic or Covalent Lab
Substance
Melt?
Dissolve?
Conduct?
Ionic or
Covalent
A
No
Yes
Yes
Ionic
B
Yes
Some
No
Covalent
C
Yes
No
No
Covalent
D
No
Yes
Yes
Ionic
Ionic or Covalent Lab
1. What happened to the “bonds” between
molecules when a substance melted?
when a substance is heated, the attractive
forces weaken/break
Ionic or Covalent Lab
1. How did the melting points of ionic compounds and
molecular compounds compare?
At 260º only the covalent substances melted. Ionic
compounds have much higher melting points than
covalent compounds.
Ionic or
Substance
Melt?
Dissolve?
Conduct?
Covalent
A
No
Yes
Yes
Ionic
B
Yes
Some
No
Covalent
C
Yes
No
No
Covalent
D
No
Yes
Yes
Ionic
Ionic or Covalent Lab
2. What do you think determines melting point?
The strength of the “bonds”/attractive forces
in a substance determines the temperature at
which it will melt.
Common Response
The melting point is determined by the
temperature where the substance melts.
What is wrong with this response?
Ionic or Covalent Lab
3. Which kind of solids dissolved easier?
Ionic compounds
Substance
Dissolve?
Ionic or
Covalent
A
Yes
Ionic
B
Some
Covalent
C
No
Covalent
D
Yes
Ionic
Ionic or Covalent Lab
Substance Conduct?
Ionic or
Covalent
A
Yes
Ionic
B
No
Covalent
C
No
Covalent
D
Yes
Ionic
Common Response
Ionic compounds conduct
because they have metals NO!!!
4. Which kind of solids
conducted electricity
better? Why do you
think this is the case?
Ionic compounds
When ionic
compounds are
dissolved, the ions are
free in solution so they
can carry electrical
current.
Ionic or Covalent Lab
Summary
Write 2-3 sentences describing what you learned
from this lab.
Common Response
In this lab I learned about the properties of ionic
and covalent compounds. You can tell them apart
by testing their properties.