Polar Bonds and Molecules Chapter 8.4

Learning Objectives Be able to use electronegativity to identify polar vs. non-polar covalent bond Draw correct dipoles on a covalent bond Draw correct net dipole on a molecular compound

Bond Polarity The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons. The nuclei of atoms pull on the shared electrons, much as the knot in the rope is pulled toward opposing sides in a tug-of-war.

Bond Polarity The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons. When the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally, and each bond formed is a nonpolar covalent bond.

Bond Polarity A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally.

Bond Polarity A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally. The more electronegative atom attracts more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

Bond Polarity The higher the electronegativity value, the greater the ability of an atom to attract electrons to itself.

Read pages 181 Define electronegativity. Copy the element symbol, atomic number and electronegativity values (pg181) of the first 20 elements onto a periodic table.

Bond Polarity Describing Polar Covalent Bonds Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0. These values are significantly different, so the covalent bond in hydrogen chloride is polar. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity Describing Polar Covalent Bonds Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0. The chlorine atom, with its higher electronegativity, acquires a slightly negative charge. The hydrogen atom acquires a slightly positive charge. δ+ δ– H—Cl Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity Describing Polar Covalent Bonds The lowercase Greek letter delta (δ) denotes that atoms in the covalent bond acquire only partial charges, less than 1+ or 1–. δ+ δ– H—Cl The minus sign shows that chlorine has a slightly negative charge. The plus sign shows that hydrogen has acquired a slightly positive charge.

Bond Polarity Describing Polar Covalent Bonds These partial charges are shown as clouds of electron density. This electron-cloud picture of hydrogen chloride shows that the chlorine atom attracts the electron cloud more than the hydrogen atom does. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

If the difference in electronegativity is between 1.7 to 4.0: Ionic Bond 0.3 to 1.7: Polar Covalent Bond 0.0 to 0.3: Non-Polar Covalent Bond

Electronegativity Scale

Using

Polar Covalent Bond vs Non-Polar Covalent Bond

Polar Covalent vs Non-Polar Covalent

Drawing Bond Dipoles: BF3

Drawing Bond Dipoles: CH3OH

Net Dipole of Molecules Dipole – separation of charges within a molecule between two covalently bonded atoms. Net Dipole – When all the dipole vectors are summed to give one overall dipole.

Let’s Practice Get out your white boards … Show the polar bonds (d- and d+) and then predict the net dipole moment of the molecule. You’ll need to use the electronegativity chart on page 177 of your textbook. PF3 - phosphorus trifluoride NH3 - ammonia (nitrogen trihydride) CCl4 – carbon tetrachloride BrF5 - bromine pentafluoride