Bonding Basics It’s really very easy!

# of Electrons gained or lost3 Before you can figure out how atoms form molecules and compounds, you need some information. You need to be able to figure out all this from the periodic table. Element Atomic Symbol Total # of Electrons1 # of Valence Electrons2 # of Electrons gained or lost3 Oxidation Number4 Iodine I 53 17 gain 1 -1 Lithium Li 3 1 lose 1 +1 Calcium Ca 20 2 lose 2 +2 Sulfur S 16 6 gain 2 -2 Boron B 5 lose 3 +3 Silicon Si 14 4 gain/lose 4 + 4 or - 4 Phosphorus P 15 gain 3 -3 1. Total number of electrons equals the atomic number. 2. The number of valence electrons is the same as the column number on the periodic table 3. Less that 4 valence electrons, electrons are lost. More than 4 valence electrons, electrons are gained. Atoms with 4 (carbon, silicon) can gain or lose. 4. Atoms lose electrons to become positive ions. Atoms gain electrons to become negative ions.

Ionic Bonds Form when one atom loses electrons and one atom gains electrons. Always form between a metal and a nonmetal. (never between two nonmetals) The oxidation numbers must add up to zero.

Example 1. Potassium + Iodine First, write the Lewis Diagram for each element. K I

Example 1. Potassium + Iodine Next, draw an arrow showing the transfer of electrons from one atom to the other. K I

Example 1. Potassium + Iodine Now, show the charges on the newly formed ions. Potassium lost an electron to become +1, and Iodine gained an electron to become -1. K+ I-

Example 1. Potassium + Iodine Finally, combine the 2 ions to form the final compound. K+ + I- KI

Example 2. Magnesium + Oxygen First, write the Lewis Diagram for each element. Mg O

Example 2. Magnesium + Oxygen Next, draw an arrow showing the transfer of electrons from one atom to the other. O Mg

Example 2. Magnesium + Oxygen Now, show the charges on the newly formed ions. Magnesium lost 2 electrons to become +2, and Oxygen gained 2 electrons to become -2. Mg2+ O2-

Example 2. Magnesium + Oxygen Finally, combine the 2 ions to form the final compound. Mg2+ + MgO O2-

Example 3. Lithium + Nitrogen First, write the Lewis Diagram for each element. Li N

Example 3. Lithium + Nitrogen Next, draw an arrow showing the transfer of electrons from one atom to the other. Notice that 1 Lithium does not provide enough electrons, so add more. N Li

Example 3. Lithium + Nitrogen A second Lithium atom provides another electron, still leaving Nitrogen 1 short. So, add another. N Li

Example 3. Lithium + Nitrogen Nitrogen now has eight valence electrons. It took 3 Lithium atoms to provide enough electrons to fill Nitrogen’s valence energy level. N Li

Example 3. Lithium + Nitrogen Now, show the charges on the newly formed ions. Lithium lost 1 electron to become +1, and Nitrogen gained 3 electrons to become -3. Li+ N3-

Example 3. Lithium + Nitrogen Finally, combine the newly formed ions to make the compound. Li+ + Li+ + Li+ + N3- Li3N

Covalent Bonds Form when one atom shares electrons with another atom. Always form between between two nonmetals. The oxidation numbers must add up to zero.

Example 1. Fluorine + Fluorine First, write the Lewis Diagram for each element. F F

Example 1. Fluorine + Fluorine Next, draw circles showing the electrons that are shared. F F

Example 1. Fluorine + Fluorine Finally, draw a line showing the bond between the atoms and then write the formula. F F F2

Example 2. 3 Hydrogen + Phosphorus First, write the Lewis Diagram for each element. H P H H

Example 2. 3 Hydrogen + Phosphorus Next, draw circles showing the electrons that are shared. H H P H

Example 2. 3 Hydrogen + Phosphorus Finally, draw lines showing the bond between the atoms and then write the formula. H H P H3P H

Example 3. 2 Hydrogen + Sulfur First, write the Lewis Diagram for each element. H S H

Example 3. 2 Hydrogen + Sulfur Next, draw circles showing the electrons that are shared. H H S

Example 3. 2 Hydrogen + Sulfur Finally, draw lines showing the bond between the atoms and then write the formula. H H S H2S