chemical bonding - folsom cordova unified school district€¦ · chapter 12 chemical bonding. ......
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Chapter 12
Chemical Bonding
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Ionic and Covalent Bonds – Who does what
Ionic Bonds – occur between a metal
cation and a non-metal anion, a metal
gives electron(s) to a non-metal.
Example: Na – Cl Fe – O
Covalent Bonds – occur between 2 non-
metals, electrons are shared by 2 nuclei.
Example: CH4 O = O
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Figure 12.1: The formation of a bond between two atoms.
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•In an H2 molecule, the electrons reside primarily in the space between the 2 nuclei.
•Each H atom in the H2 molecule pulls the electrons equally based on the electronegativity of H.
•We call this type of bond “nonpolar covalent”
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Figure 12.2: Probability representations of the electron
sharing in HF.
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•When we look at two different atoms, we see that the electrons are not shared equally, such as between H and F.
•The fluorine has a stronger attraction than the hydrogen for the shared
electrons.
•We call this bond “polar covalent”.
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Dipole Moments
Any diatomic (2 atom) molecule that has a polar bond
has a dipole moment. When a molecule has a center of
positive charge and a center of negative charge, we call
this a dipole moment
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Figure 12.5: Charge distribution
in the water molecule.
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Figure 12.6:
Polar water molecules are strongly attracted to positive ions
by their negative ends.
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Figure 12.6: Polar water molecules are strongly attracted to
negative ions by their positive ends.
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Figure 12.4:
The three possible
types of bonds. a) nonpolar covelant
(equal sharing of electrons
b) polar covelant
(unequal sharing of
electrons
c) ionic
(giving away and taking of
electrons)
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Table 12.2
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When we look at the electron configuration of atoms becoming ions, we see that they are trying to achieve a noble gas configuration.
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General Rules Ionic bonds:
◦ Metals will become positive ions, they will lose electrons
to achieve the electron configuration of the previous
noble gas before them.
◦ Non-metals will become negative ions, they will gain
electrons to achieve the electron configuration of the next
noble gas.
Covalent bonds:
◦ Atoms in covalent bonds are sharing electrons, but all the
same, they want to have noble gas configurations in their
outer valence shells so they share electrons to achieve
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Practice
Determine the electron configuration for the
following elements, and then determine who will
gain and who will lose electrons in an ionic bond.
S and Mg
Al and O
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Ion Size vs Atom Size When atoms become ions,
the size of each changes.
A cation(+) is always smaller than the parent atom.
An anion (-) is always larger than the parent atom.
To explain this, think about who has lost electrons and who has gained electrons.
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Figure 12.9:
Relative sizes of some ions and their
parent atoms.
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Lewis Structures
We must look at how many valence electrons an atom has to determine the Lewis structure of an atom.
Example: Fluorine
How many valence electrons?
Draw 1 dot for each valence electron around the symbol for the element. We draw the electrons in pairs on each of the 4 sides of the element symbol.
F
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Practice
Draw the Lewis structures for the following
elements:
He Al
H Mg
O K
C
N
S
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Lewis Dot Diagrams and Bonding
Ionic Bonds – let’s look at KBr
How many valence electrons do K and Br have?
Who is going to gain and lose electrons in this bonding interaction?
Once these 2 atoms have bonded in an ionic bond, each has gained or lost electrons, we would write the Lewis dot diagram for these as following
K+ [::Br::]-
Now you try, write the Lewis dot diagram for NaCl
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Lewis Dot Diagrams and Bonding
Covalent bonding – atoms have to share electrons to make them “happy”
The most important requirement for the formation of a stable compound is that the atoms achieve noble gas electron configurations.
Let’s look at OCl2 How many valence e-?
That’s not enough to gain or steal, so what if they share 2 pairs of electrons.
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Bond Types
Single bond involves two atoms sharing one electron
pair. Example: F-F
Double bond involves two atoms sharing two pairs of
electrons. Example: O=O
Triple bond involves two atoms sharing 3 pairs of
electrons. Example: N≡N
Remember in each case, each atom wants a noble gas
configuration with 8 outer valence electrons.
Not all the electrons involved maybe bonded, you may
find you have a lone pair of electrons, a pair of electrons
that are not bonded.
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Practice
Use Lewis dot diagrams for the following atoms
to determine the bonds:
CH4
HF
NH3
N2
O2
SO2
HINT: Some may have multiple bonds.
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