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PROPERTIES OF THE POLAR, NONPOLAR AND IONIC BONDS.

POLAR COVALENT BONDS

• Polar covalent bonds are a particular type of covalent bond.

• In a polar covalent bond, the electrons shared by the atoms spend a greater amount of time, on the average, closer to the Oxygen nucleus than the Hydrogen nucleus. This is because of the geometry of the molecule and the great electronegativity difference between the Hydrogen atom and the Oxygen atom.

• The result of this pattern of unequal electron association is a charge separation in the molecule, where one part of the molecule, the Oxygen, has a parital negative charge and the Hydrogens have a partial positive charge.

• You should note this molecule is not an ion because there is no excess of proton or electrons, but there is a simple charge separation in this electrically neutral molecule.

• Water is not the only molecule that can have polor covalent bonds. Examples of other molecules that have polar covalent bonds are Peptide bonds and amines .

• The biological consequence of polar covalent bonds is that these kinds of bonds can lead to the formation of a weak bond called a hydrogen bond.

NONPOLAR COVALENT BONDS

• The molecule methane has four Carbon-Hydrogen single covalent bonds. These covalent bonds are called nonpolar covalent bonds because

• the electrons shared by the adjacent atoms in the bonds are shared equally

• The consequence of this equal sharing of electrons is that there is no charge separation (dipole moment). Compare this to polar covalent bonds.

IONIC BOND

• A compound composed of ions.

• Metal atoms lose electrons to form positive ions, called cations, which are smaller than the original atom.

• The loss of an energy level with electrons, plus the excess positive charge draws the remaining electrons toward the nucleus and causes the electron cloud to contract even more.

• Nonmetal atoms gain electrons to form negative ions, called anions, which are larger than the original atom.

• The addition of an extra electron increases the electron-electron repulsion and causes the electron cloud to expand.

• The main Group elements (s and p orbitals) lose or gain electrons to attain a configuration like a noble gas.

• Transition elements (d orbitals) lose their s orbital electrons first and then one or more d orbital electron(s).

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