Chemistry Lecture *3T Covalent Bonding
Ionic bonds occur between metal and nonmetal atoms, in ionic
bonding, electrons are transferred -Prom one atom (metal) to
another atom (nonmetal). The atoms stick together because they
have opposite charge.
Covalent bonding occurs between two nonmetal atoms. In
covalent bonding, electrons are shared between two atoms. The
atoms stick together because the electrons that are between the
atoms act like glue holding the positive nuclei together.
For example, suppose two hydrogen atoms come close to each
other. The electron attached to one hydrogen atom will be
attracted to the nucleus o£ the other hydrogen atom. Thus, each
electron will be attracted to the nuclei o-P both atoms.
The electrons are like peanut butter and the nuclei are like two
slices o£ bread. The peanut butter holds the bread together, and
the electrons hold the nuclei together.
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Atoms will overlap orbitals to achieve a covalent bond. V=or
example, when hydrogen atoms bond, they overlap their s orbitals.
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When the two s orbitals overlap, it is as though there are two
electrons in both s orbitals, and this stabilizes the hydrogen atoms.
Remember that a Pull s orbital makes an atom more, stable.
Also, orbitals are capable o-P holding two electrons. When an
orbital with one electron overlaps with another orbital that has a
single electron, both orbitals will then have two electrons. This
makes both atoms more, stable.
Thus, when covalent bonding occurs, single electrons on one atom
will be paired up with single electrons on other atoms.
In addition, s and p orbitals on an atom will combine to -Porm a
hybrid orbital. An s orbital can combine with I, 2-, or 3 p orbitals.
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C h e m i s t r v L ect ure #37
V\/hen on s orbital combines with three p orbitals, it looks like this-
sp? hybrid
When on s orbital combines with two p orbitds, it looks like this-
hybrid
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C h e mi s i r y L e c \ ur c # 3 7
When an s orbital combines wH-h one p orbital it looks like this.
sp hybrid
In covalent bonding, hybrid orbitals will overlap with other types oP
orbitals to pair up unpaired electrons.
In addition, electrons that are paired up and shared give the
nonmetals an octet, which is a higher -Porm o-P stability.
Carbon will hybridize its orbitals in the Z1^ energy levels to -Porm
sp3 hybrid orbitals.
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#37
Below is a diagram showing how the s orbitals o£ -Pour hydrogens
overlap the sp3 orbitals o£ carbon to -Porm covalent bonds.
No-J-ice that carbon has an octet.
Below is a diagram showing how two carbons and six hydrogens
will overlap their orbitals to £orm CzHc,. Notice again that carbon
has an octet.
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Two carbon? and Pour hydrogen? can Porm covalent bond?.
For
thi? +o occur, each carbon will hybridize their ? and p orbital? to
an ?pz configuration.
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Each carbon now ha? three ?pz hybrid orbital? and a ?ingle p
orbital.
The p orbital? in both carbon? are oriented ?ide by ?ide. Thi?
allow? the top oP one p orbital to overlap the top oP the other p
orbital. The bottom halP oP each p orbital al?o overlap each
other. The overlap o£ the p orbital? in thi? Pa?hion produce? a
cre?cent ?hape above and below.
From Wikimedia Commons, the free media repository
Pi-bond.jpg (307 x 139 pixels, file size: 26 KB, MIME type: image/jpeg)
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C he m i * i r \ e c i u r e # 3
Below is a diagram showing how the p orbitals and hybrid orbitals
oP carbon overlap to -Porm GzH*. Tine p orbitals are colored pink.
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The diagram shows two types oP bonds- sigma bonds and pi bonds.
In a sigma bond the shared elec-trons are direotly between the
atoms. The diagram shows a sigma bond between the two
carbons. There are also sigma bonds between the carbons and
hydrogens. Sigma bonds are the result o-P a direct overlap
between orbitals. A single bond between atoms is a sigma bond.
A pi bond is a covalent bond where the shared electrons are not
directly between the atoms. The sideways overlap between p
orbitals creates a pi bond.
There are two covalent bonds between the carbons. When this
occurs, we have a double bond. A double bond is made oP one
sigma and one pi bond.
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L ecture #37
Two carbons and two hydrogens can bond to Porm CzHz.
For
this to occur, each carbon will hybridize its orbitals to Porm an sp
hybrid. This will give us two sp orbitals and two p orbitals.
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Each carbon now has two sp orbitals and two p orbitals.
Below is a diagram showing how the p orbitals and hybrid orbitals
oP carbon overlap to Porm GzHz. One p orbital is colored pink.
The other p orbital is colored green.
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There are three covalent bond"? between the two carbons. This
is called a triple bond. A triple bond is made o-P one sigma bond
and two pi bond?. The pi bond? are made by the sideways overlap
o£ p orbitals-
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