Electrons and Chemical Bonds Part 1 G8 Science Chapter 8.2

Our Story So Far… What is the difference between a compound and a mixture? How are covalent bonds formed? How are ionic bonds formed? Give one reason why chemical bonds are formed. Give the other reason.

Valence Electron Valence electrons are in the outermost [valence] shell of an atom. For the purpose of making chemical bonds the valence shell is the only thing that matters.

8 is a magic number For elements Boron (5) or greater, the valence shell is considered full if it has 8 electrons. This is the same number of valence electrons as most noble gasses. For elements less than Boron, the valence shell is considered full if it has 2 electrons. Atoms will get rid of, gain, or share electrons to get a full valence shell.

Hydrogen is special Hydrogen has one valence electron. It may get rid of the electron and have a positive charge. It may gain an electron and have a negative charge. It may share electrons to get two valence electrons. What kind of bond is this?

Ionic Bond View of Valence Electrons Why does this have a positive charge? Why does this have a negative charge?

Periodic Table View of Valence Electrons As you go L-R on the table, each group [except transition metals] has one more valence electron. The rule is: Period 1 has 1 valence electron Period 2 has 2 valence electrons Period 13-18 have (group # minus 10) valence electrons As you go top to bottom on the table, each period has one more shell.

Your Turn How many valence electrons does carbon have? How many valence electrons does sodium have? How many valence electrons does neon have? How many valence electrons does chlorine have?

Lewis Dot Diagrams Lewis dot diagrams are a way of keeping track of valence electrons when figuring out how compounds are formed. Start by writing the atomic symbol. Surround it by valence electrons, no more than 2 per side.

Lewis Dot Diagram and Chemical Bonding Atoms ‘want’ to have a full valence shell [octet rule]. Lewis dot diagrams show you the empty places. Move the atoms so all the empty places in both atoms share the valence electrons on that side. Some people draw each line as two dots. = is :: I like the lines because they show the electrons are shared on both sides. And save the dots for ionic bonds.

Your Turn Draw the Lewis dot diagram for F2. What kind of bond is this? Draw the Lewis dot diagram for BeO. What kind of bond is this? Draw the Lewis dot diagram for H2O. What kind of bond is this?

Activity Handout Side 1 is just drawing the Lewis dot diagrams. Side 2 is using Lewis dot diagrams to draw ionic and covalent bonds. Due at end of class. If you get done early, work on homework – do not socialize.