Covalent Bonding

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Atoms bond together because they want a stable electron arrangement consisting of a full outer energy level.
Two ways that atoms can bond together are ionically & covalently.
A covalent bond is a chemical bond that results from the sharing of the valence electrons.
Covalent bonds are usually formed between elements close to each other on the periodic table and nonmetallic elements.

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A molecule is formed when 2 or more atoms bond covalently.
Example
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HI
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F
2
Practice problems
1. HBr 2. O
2
3. H
2
O

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Diatomic molecules are molecules of like atoms. Diatomic molecules include hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, & iodine.
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Write the formulas & structures for the diatomic molecules.

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The number of covalent bonds that these groups form are:
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Halogens  single covalent bond
Group 6A  double/two covalent bond
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Group 5A  triple/three covalent bond
Group 4A  four covalent bonds

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Practice
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H F
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O Cl
2
H
2
S
N
2
P H
3
Si H
4

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Single covalent bonds are also called sigma bonds, symbolized by the Greek letter s
A sigma bond results when orbitals overlap.
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 s orbitals can overlap s orbitals s orbitals can overlap p orbitals p orbitals can overlap p orbitals

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Multiple covalent bonds occur when more than one pair of electrons are shared.
A pi bond, p , is formed when parallel orbitals overlap to share electrons.
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A double bond is made of 1 sigma bond & 1 pi bond
A triple bond is made of 1 sigma bond & 2 pi bonds

Draw the lewis dot structure for each molecule.
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1. PH
3
2. H
2
S
3. HCl
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4. CCl
4
5. SiH
4
6. CO
2

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If H
2
O is water, what is H
2
O
4
?
Drinking, bathing, washing, swimming…

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The strength of covalent bonds depend on the length of the bond, the distance between the bonded nuclei.
Bond length is determined by the size of the atoms & the number of shared electron pairs.
As the number of shared pairs increases, the bond length decreases.

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The shorter the bond, the stronger the bond.
Energy is released when a bond forms & energy is added to break a bond.
Which has a shorter bond? H
2 or S
2
The amount of energy needed to break a bond is the “ Bond Dissociation Energy ”
Among F
2
, O
2
, & N
2
, which would have the greatest bond dissociation energy? Least?

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Endothermic reactions  occur when a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the product molecules
Exothermic reactions  occur when more energy is released forming new bonds than is required to break bonds in the initial reactants

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Exothermic Rxn
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Endothermic Rxn

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Naming Binary Molecular Compounds
1st element—use entire element name
2nd element—use root word & “ ide ” use prefixes to indicate # of atoms for each element
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 prefixes mono—1 di—2 tri—3 tetra—4 penta—5 hexa—6 hepta—7 octa—8 nona—9 deca--10

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**NEVER USE mono WITH 1ST ELEMENT**
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Example
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N
2
Cl
3
CO
2
Practice
1. P
2
O
5
2. NO
2
3. CO
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Common names of some molecular compounds— p. 249
** Worksheet “ Naming molecular compounds ”

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What is the name for H
2
O?
What is the name for CH
2
O?
Sea water

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Naming acids
Binary acids—hydrogen plus one other element
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Hydro + root of 2nd element + ic acid
1.
HCl  hydrochloric acid
2.
3.
4.
HBr  hydrobromic acid
H
2
S  hydrosulfuric acid
Hydroiodic acid 

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Oxyacids—contain hydrogen & oxygen and one other element
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Root of other element + ic acid
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H
2
CO
3

H
2
SO
4

HC
2
H
3
O
2

Phosphoric acid 
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Nitric acid 
** Worksheet “ Naming acids ”

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Structural formulas use letter symbols & bonds to show relative positions of atoms.
Hydrogen is always a terminal atom because it can bond with only 1 other atom.
Resonance is a condition that occurs when more than one valid Lewis structure can be written for a molecule or ion.

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Example
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HCl
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SO
2
Practice
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1. SO
3
2. O
3

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A coordinate covalent bond forms when one atom donates both electrons to be shared.

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Molecular shape is determined by the overlap of orbitals that share electrons.
The VSEPR model is used to determine the molecular shape of the molecule. VSEPR stands for
Valence
Shell
Electron
Pair
Repulsion model.

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F
2 has linear shape
CO
2 has linear shape
BH
3 has trigonal planar shape
CF
4
NH
3 has tetrahedral shape has pyramidal shape
H
2
O has bent shape

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Hydridization is a process where atomic orbitals are mixed to form new, identical hybrid orbitals.
Carbon is the most common element that undergoes hybridization.
The hybrid orbital of carbon is called sp 3 .
It takes shape to look like a tetrahedral.

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Remember that electronegativity is defined as the tendency of an atom to attract electrons.
Fluorine has the highest EN at 3.98 and
Francium has the lowest EN at 0.7.

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Polar covalent bond is when electrons are unequally shared—large difference in EN.
Electrons spend more time around the element that is more EN. The more EN element has a partial negative charge. A polar covalent bond is also called a dipole.
Electronegativity occurs in molecules.
For example H
2
O & HCl
Page 263

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Nonpolar covalent bond is when electrons are shared equally—have small or no EN differences. Symmetrical molecules with balanced charges are nonpolar. (CCl4)
These are pure covalent bonds.
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Ionic bonds generally form when EN differences are 1.7 or greater.

Electronegativity difference
0.00 - 0.4
0.5 – 1.6
1.7 – 3.2
Bond Type
Nonpolar covalent
Polar covalent ionic

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Example:
HCl
1.
2.
3.
4.
Practice:
SCl
2
H
2
S
CF
4
CS
2

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“ like dissolves like ”
Many different types of forces between molecules.
**Worksheet “ Shape/polarity of molecules ”

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Mainly gases (some liquids), melt/vaporize easily, hardness varies.
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Oxygen gas, acids, parafinn, graphite, diamonds