forming molecular bonds. what is a covalent bond? the chemical bond that results from the sharing...
TRANSCRIPT
Covalent Bonding
Forming Molecular Bonds
What is a covalent bond?
The chemical bond that results from the sharing of electrons Non-metals combine to acquire a full valence
shell of 8 valence electrons Example:
7 valence e- 8 valence e-
Degree of sharing
Non-polar Covalent
Polar Covalent
Ionic
e- are shared equally
e- shared unequally
one atom takes e-
from another
Na
Cle-
Types of covalent bonds
Single Covalent bonds- (also called sigma bonds) When a single pair of electrons is shared Ex: H H
Group 7A: will form single covalent bonds Group 6A: will form two single covalent bonds Ex: H2O
Group 5A: will form three single covalent bonds Ex: NH3-
Ammonia Group 4A: will form four single covalent bonds Ex: CH4
- methane
Types of covalent bonds continued…
Multiple covalent bonds: Double or Triple bonds
Double covalent bond- when two pairs of electrons are shared. Ex: O2 (draw lewis structure)
Triple covalent bond- formed when three pairs of electrons are shared between two atoms. Ex: N2 shares three pairs of electrons.
Pi bonds π- multiple bond consists of one sigma and one pi bond.
triple bond- one sigma and two pi bonds.
The shorter the bond the stronger the bond. Triple bonds are shorter.
Lewis dot structuresRules for drawing dot structures:
1. Calculate the number of valence e- each atom contributes. Divide this number in half to get the number of pairs.
:::: :
:
ex: CBr4 C = 4
Br = 7 x 4 = 28
32 e-
16 prs
3. Use pairs of e- (as single covalent bonds) to attach all the other atoms to the center atom.
ex: CBr4
C Br
Br
Br
Br
4. Put lone pairs of e- on the outside atoms until each atom has 8 electrons (4 pairs) or 1 pair on hydrogen.
5. Put any leftover pairs on the center atom so that it also has 4 prs around it.
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:
:
: :
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Lewis dot structures continued…
2. Decide which element will be the center at usually the one that has fewer atoms or the lower electronegativity
CH4 SO2 PCl5
Lewis dot structures continued…
CH4
What is the central atom?
C
How many valence electrons does it have? 4How many hydrogens are there? 4 How many valence electrons do each have? 1
H
H
H
H
Now, join the electrons with a bond
How many sigma bonds are there?
4
diatomic elements
H2 O2 Br2 F2 I2 N2 Cl2
Octet Rule:
atoms share electrons in order to have 8 valence e- (2 for hydrogen)
Naming Covalent Compounds
Covalent compounds are named by adding prefixes to the element names.
‘Covalent’ means both elements are nonmetals.
A prefix is added to the name of the first element in the formula ONLY if more than one atom of it is present.
A prefix is ALWAYS added to the name of the second element in the formula
The second element will use the form of its name ending in ‘ide’.
Naming Covalent CompoundsPrefixes
Subscript Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
Subscript Prefix
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-
Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.
Naming Binary Covalent Compounds: Examples
N2S4dinitrogen tetrasulfide
NI3 nitrogen triiodide
XeF6 xenon hexafluoride
CCl4 carbon tetrachloride
P2O5 diphosphorus pentoxide
SO3 sulfur trioxide
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
* Second element ends ‘ide’
* Drop –a & -o before ‘oxide’
Writing Chemical Formulas: A Review
I. Ionic Compounds
II. Covalent Compounds
Writing Formulas for Covalent Compounds
The names of covalent compounds contain prefixes that indicate the number
of atoms of each element present.
Remember: Binary compounds contain only two elements, both of which are nonmetals When in covalent compounds
atoms DO NOT have chargesSubscripts are determined directly from the prefixes in the
name.
• First element:• if there is only one atom of that element in the formula (its subscript will be
1) and there should NOT be a prefix
• Second element: • will ALWAYS have a prefix• will ALWAYS end in -ide
Writing Formulas for Binary Covalent
Compounds: Examplesnitrogen dioxide NO2
diphosphorus pentoxide P2O5
xenon tetrafluoride XeF4
sulfur hexafluoride SF6
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
7 hepta
8 octa
9 nona
10 deca
* Second element ends in ‘ide
* Drop –a & -o before ‘oxide’
Writing Formulas: Practice
carbon tetrafluoride CF4
Na3PO4sodium phosphate
Cu2SO4copper (I) sulfate
Analysis If “Yes”
The compound is covalent: the
prefixes give the subscripts.
* Are there prefixes present
The compound is ionic:
subscripts must be
determined by balancing
charges
prefixes covalent prefixes indicate subscripts
metal ionic balance charges 3 Na1+ needed for 1 PO43-
metal present ionic balance charges 2 Cu1+ needed for 1 SO42-
Al2S3aluminum sulfidemetal present ionic balance charges 2 Al3+ needed for 3 S2-
N2O5dinitrogen pentoxideprefixes covalent prefixes indicate subscripts
NH4NO3ammonium nitratepolyatomic ion present ionic balance charges
1 NH41+ needed for 1 NO3
1-
PbO2lead (IV) oxidemetal present ionic balance charges 1 Pb4+ needed for 2 O2-
Fe2(CO3)3 iron (III) carbonatemetal present ionic balance charges 2 Fe3+ needed for 3 CO3
2-