Chemical Bonds Notes Atoms combine to form compounds by holding pairs of electrons between them. *(Draw the picture below) The paired electrons are known as a chemical bond. H H C H H

Chemical Bond Classification Chemical bonds are classified by the way the electrons are held between the atoms that are bonding to each other.

Chemical Bond Classification Electrons can be held in a bond by one of two ways: – Electrons are equally shared by both atoms. (Covalent) – Electrons are “exchanged” from one atom to another forming ions. (Ionic)

Properties of Covalent Bonds Covalent bonds occur between two non-metal atoms. In covalent bonds e lectrons are shared by the atoms involved in the bond.

Examples of Covalent Bonds Examples of compounds formed with covalent bonds include: – Hydrogen gas (H 2 ) – Ammonia (NH 3 ) – Large biological molecules such as glucose (C 6 H 12 O 6 ).

Properties of Ionic Bonds Ionic bonds occur between a metal atom and a non-metal atom. In ionic bonds e lectrons are exchanged or transferred from the metal atom to the non-metal atom. After the transfer of electrons, both atoms become oppositely charged, keeping both atoms together (bonded).

Examples of Ionic Bonds Examples of compounds formed with ionic bonds include: – Sodium chloride (NaCl) – Strontium sulfide (SrS)

Next steps…if you’ve mastered bonding All elements have a certain ELECTRONEGATIVITY This describes tendency of an atom to attract electrons towards itself. (aka-it’s hunger for electrons) High Electronegativity = High attraction/hunger for electrons. Low Electronegativity = Low attraction/hunger for electrons.

Electronegativity differences and bonding If atom A is very electronegative (electron hungry) and atom B is not, the electrons will move toward atom A and this will result in an IONIC BOND where the electrons are transferred. If atom A’s electronegativity is only a little greater than atom B, they will share the electrons unevenly (POLAR COVALENT BOND) (electrons will be closer to atom A and one end of the group is more negative than the other.) If atom A and atom B have the same or very similar electronegativities the electrons are evenly shared and it makes a NONPOLAR COVALENT BOND.

ELECTRONEGATIVITY DIFFERENCES

Electronegativity Difference Type of BondElectrons 0-.5Non Polar Covalent Electrons equally shared Greater than Polar CovalentUneven sharing of electrons Greater than 1.7IonicElectrons are Transferred

Some periodic tables will also list the electronegativity.

Ionic Bond or Covalent Bond 1.NaCl 2.FeCl 3 3.SO 3 4.H 2 O 5.MgO Ionic Covalent Ionic How do you know? Look at the atoms and determine whether there are metal atoms present or not. (Metal & Nonmetal=Ionic!)

Practice!! Get your whiteboards Ionic Bonding Potassium and Fluorine Magnesium and Iodine Sodium and Oxygen Sodium and Chlorine Calcium and Chlorine Aluminum and Chlorine Covalent Bonding Hydrogen and Hydrogen Hydrogen and Oxygen Chlorine and Chlorine Carbon and Hydrogen Oxygen and Oxygen Carbon and Oxygen