|
Polar Covalent
Bond.
VBS Home page,VBS
Course Navigator, Basic chemistry, Chemical
bonds, Previous Page, Next
Page,top of page
 These
bonds are in between covalent and ionic bonds in that the atoms share electrons
but the electrons spend more of their time around on atom versus the others
in the compound. This type of bond occurs when the atoms involved differ
greatly in electronegativity. The most familiar example is water. Oxygen
is much more electronegative than hydrogen, and so the electrons involved
in bonding the water molecule spend more time there.
The fact that water is a polar covalently bonded moleccule has a number
of implications for molecules that are disolved in water. In particular,
molecules with polar covalent bods can break apart when they encounter
water molecules. They are broken apart because of the electrical attraction
between the dissimilar charges of the molecules. Also, since ionically
bonded molecules involve ions with opposite charges, water with its polar
covalent bonds can separate ions from each other and then surround the
ions which prevents them from recombining. The properties
of water all relate to this polar covalent bonding. Indeed the sorts
of so called hydrophilic
and hydrophobic interactions
water has with varios organic compounds depend on the nature of the polar
covalent bond in water. Previous
Page
Hydrogen
Bond.
The fact that the oxygen end of a water molecule is negatively charged
and the hydrogen end positively charged means that the hydrogens of one
water molecule attract the oxygen of its neighbor and vice versa. This
is because unlike charges attract. This largely electrostatic attraction
is called a hydrogen bond and is important
in determining many important properties of water that make it such an
important liquid for living things. Water can also form this type of bond
with other polar molecules or ions such as hydrogen or sodium ions. Further,
hydrogen bonds can occurr within and between other molecules. For instance,
the two strands of a DNA molecule are held together by hydrogen bonds.
Hygrogen bonding between water molecules and the amino acids of proteins
are involved in maintaining the protein's proper shape. Previous
Page
 |
This picture represents a small group of water molecules.
Hydrogen bonds between unlike charges are shown as lines without
arrows on the ends. The double arrowed lines represent the fact
that like charges repell each other. Both hydrogen bonds and
the repelling forces balance each other and are both are important
in determining the properties of water. |
Page Top |
Ionic, Covalent,
Polar covalent, Hydrogen bond
VBS Home page,VBS
Course Navigator, Basic chemistry, Chemical
bonds, Previous Page, Next
Page,top of page
Top of Page revised 10/7/01
|
|
|
Ionic
bonds arise from elements with low
electronegativity(almost empty outer shells) reacting with
elements with high electronegativity (mostly
full outer shells). In this case there is a complete transfer of electrons.
Previous Page
