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LecturePLUS Timberlake 1
Covalent Bonding
LecturePLUS Timberlake 2
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.
LecturePLUS Timberlake 3
EXAMPLE
Two Hydrogen atoms move close together to SHARE valence electrons.
H + H H H
LecturePLUS Timberlake 4
For example, NITROGEN and OXYGEN can form several different compounds:
NO NO2 NO3 N2O
N2O2 N2O3 N2O4 N2O5
If we named this NITROGEN OXIDE, which one would we be talking about?
The SAME TWO ATOMS can share DIFFERENT NUMBERS of electrons.
• There is more than one possible formula combination for the same group of atoms.
LecturePLUS Timberlake 5
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.
LecturePLUS Timberlake 6
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!
LecturePLUS Timberlake 7
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
LecturePLUS Timberlake 8
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 Hexaoxide
LecturePLUS Timberlake 9
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
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
LecturePLUS Timberlake 10
LecturePLUS Timberlake 11
1. CO carbon monoxide
2. CO2 carbon dioxide
3. PCl3 phosphorus
trichloride
4. CCl4 carbon tetrachloride
5. N2O dinitrogen monoxide
LecturePLUS Timberlake 12
MORE PRACTICE PROBLEMS
Write the correct formula for the following Covalent compounds.
1. triphosphorus monoxide2. phosphorus pentoxide3. diphosphorus pentoxide
4. dichlorine heptoxide5. dichlorine tribromide6. silicon tetroxide 7. carbon tribromide
8. antimony disulfide
**STOP HERE**
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.
LecturePLUS Timberlake 14
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.
LecturePLUS Timberlake 15
Electronegativity Values
LecturePLUS Timberlake
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.
Practice Problems Use Eneg values to predict the type of bond that would form between each
pair of atoms:
1. Ca and Br ____________ 2. H and O ______________ 3. Pb and S ______________ 4. Au and S_______________ 5. Sn and I ______________ 6. C and H _______________
7. B and H _______________ 8. Fr and F _______________ 9. N and Al _______________
LecturePLUS Timberlake 17