Homonuclear

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Homonuclear Heteronuclear bonds
Hydrogen peroxide (H2O2)
Hydrazine (N2H4)
Ethane (C2H6)
Homonuclear bonds
Hetronuclear bonds
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Polar bonds
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IONIC COMPOUNDS
Salt crystals are repeating patterns of
positive cations and negative- anions held
together by electrostatic attraction.
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COVALENT COMPOUNDS
Biological molecules are covalently bound Most
consist of the non-metals Carbon, Oxygen,
Hydrogen, and Nitrogen.
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SO.. Ionic and covalent bonds are very
different, but how do we predict if a bond will
be ionic or covalent?
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electronegativity
The ELECTRONEGATIVITY of an element helps us
understand the difference between ionic and
covalent bonding

• Electronegativity is the measure of the ability
  of an atom in a bond to attract electrons.

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• With only a few exceptions, electronegativity
  values increase as you move from left to right in
  any period of the periodic table.

• Within any group, electronegativity values
  decrease as you go down the group.

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That means that the most electronegative
elements are in the upper-right corner of the
table.
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Every element has an electronegativity value
Francium has the lowest electronegativity 0.7
Fluorine has the highest 4.0
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Elements with a HIGH electronegativity have a
STRONG pull on electrons.
Elements with a LOW electronegativity have a WEAK
pull on electrons.
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difference in electronegativity
When two atoms bond their DIFFERENCE in
electronegativity determines the bond type.
A large difference in electronegativity means one
atom will win the tug of war and take the
electrons completely. This is an ionic bond.
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When the electronegativity of two bonding atoms
is very similar, neither atom wins the tug of
war and the electrons are shared equally.
This produces a covalent bond
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In a true covalent bond electrons are shared
equally
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IONIC COVALENT
Transfer electrons Share electrons
Between an atom of high electronegativity and an
atom of low electronegativity
Between two atoms of equal or very close
electronegativities
NaCl N2
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If the electronegativity difference between two
bonded atoms is very high the bond is ionic.
If the electronegativity difference is very low
the bond is covalent.
What if the difference in electronegativity
between the two bonded atoms is in-between?
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A POLAR COVALENT BOND occurs when two atoms share
electrons unequally.
The atom with a high electronegativity value
holds the bonding electrons more often, but it
doesnt remove the electrons completely.
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Are the bonds polar covalent,
non-polar covalent, or
ionic? 1) H-C 2) K-Cl 3) O-F 4)
Cl-Cl 5) C-N 6) S-O 7) B-S
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A polar bond has a partial positive charge (?)
and a partial negative charge (?-)
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The N-H bond is polar, with N being the most
electronegative.
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?-
?
?
?
The N-H bond is polar, with N being the most
electronegative.
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Bond polarity and 3D shape determine if a
molecule is polar
Bond polarity --- When a bond has a partial
negative charge on one atom and a partial
positive charge on the other atom.
Molecule shape--- the arrangement of atoms in
three dimensions (3-D)
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A polar molecule has polar bonds and asymmetry
Polar bonds Polar molecule Asymmetry
- has different sides
Polar bonds Non-polar
molecule Symmetry- all sides are the same
d-
d-
Positive side
d
d
negative side
d-
d-
d-
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If the electrons are not distributed equally, the
molecule is said to be polar.
The molecule has a negative end and a positive
end.
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Polar molecules are affected by electric fields
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It has two poles and is polar it has a
measurable dipole moment.
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POLAR MOLECULES INTERACT!!
A partial positive charge (?) is attracted to
negative ions and

negative partial charges
(?-) of other polar bonds.
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POLAR MOLECULES INTERACT!!
A partial negative charge (?-) is attracted to
positive ions and

partial positive charges
(?) of other polar bonds.

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Water is a molecule that consists of two polar
covalent O-H bonds.
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The electrons are not distributed evenly so the
water molecule is polar. The negative end of the
molecule is the oxygen end. O is more
electronegative than H and pulls the negative
electrons toward itself. Also, there are two lone
pairs around oxygen.
negative end
positive end
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Na(aq) A dissolved sodium ion
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Practice- Draw the 3D structures for these
molecules and label the bond polarity and the
molecule polarity.

• H2O
• CH4
• CH3F
• CH3CH3
• CH3CH2OH
• 6. NH3

7. CO2 8. CH2CH2 9. HCN 10. 11.