Transcript Covalent Bonding Notes 12-10-14

Covalent Bonding
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Covalent Bonds
 Recently we worked with IONIC COMPOUNDS which form
when positive CATIONS combine with negative ANIONS.
 Not ALL compounds involve ions.
 In COVALENT BONDING, valence electrons are shared
between two atoms.
 Electrons are NOT transferred from one atom to another, so they do not
develop “+” or “-” charges as do ions.
 Generally form between TWO NONMETAL ELEMENTS from
GROUPS 14, 15, 16, and 17 but can involve elements FROM
OTHER GROUPS.
 Covalent compounds are also called MOLECULAR
COMPOUNDS.
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EXAMPLE
Two Hydrogen atoms move close together to
SHARE valence electrons.
H +
H
H H
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The SAME TWO ATOMS can share DIFFERENT NUMBERS of
electrons.
• There is more than one possible formula combination for the
same group of atoms.
For example, NITROGEN and OXYGEN can form
several different compounds:
NO
N2O2
NO2
N2O3
NO3
N2O4
N2O
N2O5
If we named this NITROGEN OXIDE, which one
would we be talking about?
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Naming Covalent (Molecular) Compounds
In order to name a COVALENT compound, we
follow the same basic rules as for BINARY
IONIC compounds….with one added step.
Since the same group of atoms can bond in
different proportions, we must indicate HOW
MANY OF EACH ATOM there is in the
compound.
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Naming Covalent Compound

1. Name the first element by its name,
adding a NUMBER PREFIX ONLY IF THERE
IS MORE THAN ONE ATOM.

2. Name the second element by its name,
but:


A. Change the ending to IDE.
B. Add a NUMBER PREFIX to tell how
many, even if there is only one!
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Number Prefixes for Covalent Compounds
1 – Mono
2 – Di
3 – Tri
4 – Tetra
5 – Penta
6 – Hexa
7 – Hepta
8 – Octa
9 – Nona
10 –Deca
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
When adding prefixes, the “A” or “O” of
the prefix may need to be DROPPED if the
element starts with a VOWEL, such as:

Hexa added to OXIDE becomes:
 Hexoxide
NOT
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Hexaoxide
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Practice Problems
Example
Write the formula for:
Trinitrogen Pentachloride
Tri = 3
Penta = 5
nitrogen
chloride = chlorine
So this compound needs 3 NITROGEN and 5 CHLORINE
The 3 and 5 are the SUBSCRIPTS in the formula.
N3Cl5
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WRITE the formula for these Covalent Compounds:
(To make it easier, prefixes are colored in these practice
problems)
Click HERE for a PERIODIC TABLE.
1. carbon monoxide
2. carbon dioxide
3. phosphorus trichloride
4. carbon tetrachloride
5. dinitrogen monoxide
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1. CO
carbon monoxide
2. CO2
carbon dioxide
3. PCl3
phosphorus trichloride
4. CCl4
carbon tetrachloride
5. N2O
dinitrogen monoxide
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MORE PRACTICE PROBLEMS
Write the correct formula for the following Covalent
compounds.
1.
2.
3.
4.
5.
6.
7.
8.
triphosphorus monoxide
phosphorus pentoxide
diphosphorus pentoxide
dichlorine heptoxide
dichlorine tribromide
silicon tetroxide
carbon tribromide
antimony disulfide
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**STOP HERE**
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Diatomic Elements


Some elements, when not bonded to other
elements, bond to another atom of their own
kind. These are known as DIATOMIC
ELEMENTS.
There are 8 naturally existing diatomic
elements:



ALL of family 17 (Halogen Family).
Oxygen, Nitrogen and Hydrogen
These elements should be written as:

F2, Cl2, Br2, I2, At2, O2, H2, N2 when they are NOT
part of a compound.
Pure vs Polar Covalent

When two atoms share an electron, the
ELECTRONEGATIVITY value of each atom
determines how closely the electron is pulled
toward one atom or the other.

Recall Electronegativity [Eneg] is the measure of
the attraction one atom has for another’s valence
electrons.

SEE CHART NEXT SLIDE FOR Eneg Values.
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Electronegativity Values
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Determining Bond Type

To determine the type bond between any two
atoms, find the difference between their Eneg values:
0 to 0.5 - PURE Covalent – the e- is shared at an
equal distance between both atoms.
0.51 to 1.99 – POLAR Covalent – the e- is shared
closer to one atom than the other…this gives the
atom the e- is closest to a slightly NEGATIVE
charge [delta -] and the one the e- is father away
from a slightly POSITIVE charge [delta +].
2.0 or greater – the e- is completely transferred from
one atom to the other and forms an IONIC BOND.
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Practice Problems

Use Eneg values to predict the type of bond that would form between each
pair of atoms:

1.
3.
5.
7.
9.

Ca and Br ____________
Pb and S ______________
Sn and I ______________
B and H _______________
N and Al _______________
2.
4.
6.
8.
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H and
Au and
C and
Fr and
O ______________
S_______________
H _______________
F _______________
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