Transcript Bonding and Electronegativity

Homonuclear & Heteronuclear
bonds
Ethane (C2H6)
Homonuclear bonds
Hydrazine (N2H4)
Hydrogen peroxide
(H2O2)
Hetronuclear bonds
Polar bonds
IONIC COMPOUNDS
Salt crystals are repeating patterns of
positive+ cations and negative- anions
held together by electrostatic attraction.
COVALENT COMPOUNDS
Biological molecules are covalently bound
Most consist of the non-metals Carbon, Oxygen,
Hydrogen, and Nitrogen.
SO…..
Ionic and covalent bonds are very different,
but how do we predict if a bond will be ionic
or covalent?
The ELECTRONEGATIVITY
of an element
electronegativity
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.
• 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.
That means that the most
electronegative elements are in the
upper-right corner of the table.
Every element has an electronegativity value
Francium has the lowest electronegativity 0.7
Fluorine has the highest 4.0
Elements with a HIGH electronegativity
have a STRONG pull on electrons.
Elements with a LOW electronegativity
have a WEAK pull on electrons.
When two atoms bond their DIFFERENCE in
difference
electronegativity determines
thein
bond type.
electronegativity
A large difference in electronegativity
means one atom will win the “tug of war” and
take the electrons completely.
This is an ionic bond.
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
In a true covalent bond
electrons are shared equally
IONIC
COVALENT
Transfer electrons
Share electrons
Between an atom of
high
electronegativity
and an atom of low
electronegativity
NaCl
Between two
atoms of equal or
very close
electronegativities
N2
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?
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 doesn’t remove the electrons
completely.
Are the bonds polar covalent,
non-polar covalent, or ionic?
1) H-C
2) K-Cl
5) C-N
3) O-F
6) S-O
4) Cl-Cl
7) B-S
A polar bond has a partial positive charge
(+) and a partial negative charge (-)
The N-H bond is polar, with N
being the most electronegative.

+

+

+

The N-H bond is polar, with N being the most
electronegative.
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)
A polar molecule has polar bonds
and asymmetry
Polar bonds
Non-polar molecule
Polar bonds
Polar molecule
δPositive
side
δ+
δ-
δ-
δSymmetry- all sides are
the same
δδ+
negative
side
Asymmetry- has
different sides
If the electrons are not
distributed equally, the
molecule is said to be
polar.
The molecule has
a negative end and
a positive end.
Polar molecules are affected by
electric fields
It has two poles and is polar;
it has a measurable dipole moment.
POLAR MOLECULES INTERACT!!
A partial positive charge (+) is attracted to
negative ions
and
negative partial charges
(-) of other polar bonds.
POLAR MOLECULES INTERACT!!
A partial negative charge (-) is attracted to
positive ions
and
partial positive charges
(+) of other polar bonds.
+
Water is a molecule that consists of two polar
covalent O-H bonds.
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
Na+(aq)
A dissolved sodium ion
Practice- Draw the 3D structures for these
molecules and label the bond polarity and the
molecule polarity.
1. H2O
7. CO2
2. CH4
8. CH2CH2
3. CH3F
9. HCN
4. CH3CH3
10.
5. CH3CH2OH
11.
6. NH3