What are we learning? C.5B: Use the Periodic Table to identify and explain the properties of chemical families, including alkali metals, alkaline earth metals, halogens, noble gases, and transition metals. C.5C: Use the Periodic Table to identify and explain periodic trends, including atomic ionic radii, electronegativity, and ionization energy. (BEGIN)

In your science notebook answer the following questions: What chemical trend do you notice as each alkali metal is reacting with water? Make sure to use the words group, alkali metal, and reactivity. Predict what would happen if Rb, Cs, and Fr were added to water.

Let’s watch the video to check your answer! http://video.google.com/videoplay?docid=-2134266654801392897#

Valence Electrons

Valence Electrons   Valence electrons are the number of electrons in the outermost energy level. All elements within a group have the same number of valence electrons These electrons are available to be lost, gained, or shared in the formation of chemical compounds. Found in the s and p orbitals of the highest energy level. Often located in incompletely filled energy levels.

How do I find the number of Valence Electrons? To find the number of valence electrons, underline the largest number as often as it occurs and add the superscripts. Example: Cl – 1s2, 2s2, 2p6, 3s2, 3p5 – 7 valence electrons Example: Mg - 1s2, 2s2, 2p6, 3s2 – 2 valence electrons Example: Kr – 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6 – 8 valence electrons Example: U – 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6, 6s2, 4f14, 5d10, 6p6, 7s2, 5f4 – 2 valence electrons

Shortcut to finding Valence Electrons! Group 1 1 valence electron Group 2 2 valence electrons Group 13 3 valence electrons Group 14 4 valence electrons Group 15 5 valence electrons Group 16 6 valence electrons Group 17 7 valence electrons Group 18 8 valence electrons

WARNING there is no shortcut for finding valence electrons for transition or inner-transition metals The number of valence electrons for elements from Groups 3-12 can have different values based on the conditions of chemical reactions. This is also true for a small number of the metals in Groups 13-16

Reactivity of groups Elements in the same group/family have the same number of valence electrons. If you’ll remember from last class, elements in the same group have the similar physical and chemical properties; they react the same way (think alkali metal demo). This has to do with the number of valence electrons!

Oxidation Numbers Remember that all atoms want to have a full outermost energy level of 8?.....

Oxidation Numbers The electrical charge resulting from atoms gaining or losing electrons to fill their outermost s and p orbitals. All uncombined elements have an oxidation number of zero (0) Metals lose electrons and have (+) oxidation numbers; nonmetals gain electrons and have (–) oxidation numbers All Noble Gases have an oxidation number of zero (0).

Ions Ion – a charged particle or molecule created through the loss or gain of valence electrons Cation – positively charged particle or molecule created through the loss of valence electrons as a result of ionization Anion – negatively charged particle or molecule created through the gain of valence electrons as a result of electronegativity

Making atoms! Make a neutral lithium atom. How many protons should it have? How many electrons? In order for Li to be stable, would it be easier to add 7 electrons or take away 1? What would be Li’s oxidation number?

Making atoms! Make a neutral atom of fluorine. How many protons? How many electrons? Should you add valence electrons or take away to fill it’s outermost s and p orbital? What would be it’s oxidation number?

Make models of each of the following atoms and determine it’s oxidation number. Record answers in your notebook. Element Group #/Name # Valence Electrons Oxidation Number Lithium Sodium Beryllium Magnesium Boron Aluminum Oxygen Sulfur Fluorine Chlorine Neon Argon Explain trends you see going down the group and across the period. Predict oxidation numbers for nitrogen, strontium, and Iodine.

In your notebook… Explain why metals tend to have positive oxidation numbers. Explain why non metals tend to have negative oxidation numbers. Explain why the noble gases have an oxidation number of zero.

Oxidation Number Typically, it’s the number of electrons needed to be lost or gained in order to complete a stable electron configuration. (How many electrons do I need to gain or lose in order to have a full outermost energy level of 8?) metals need to lose electrons. They have (+) oxidation numbers nonmetals need to gain electrons. They have (–) oxidation numbers All Noble Gases have an oxidation number of 0.

How do I find an element’s Oxidation Number? Oxygen, for example, has 6 valence electrons. It needs to gain two electrons in order to get 8… Its oxidation number typically is -2. Aluminum has 3 valence electrons. It needs to lose three electrons… Its oxidation number typically is +3.

Making sense of valence electrons and oxidation numbers!

Group 1- Alkali Metals Alkali metals are the most reactive metals because they only have one valence electron and it is “easier” for them to lose that one electron. They have similar chemical and physical properties because they have 1 valence electron. In our demo, all the alkali metals reacted with water. (reactivity = chemical property)

Group 17 - Halogens Halogens are the most reactive nonmetal since they have 7 valence electrons. It is easier for them to gain one electron. They have similar chemical and physical properties because they ALL have 7 valence electrons

Noble Gases Noble Gases are non reactive since they have all their valence electrons. They do not need to gain or lose any electrons. They have the maximum number of electrons in their outermost energy levels.

On your periodic table, let’s label the valence electrons and oxidation number trends! Valence electrons: 1 2 3 4 5 6 7 8 Oxidation #: +1 +2 +3 +4 -3 -2 -1 0

Review Time! Which group has 2 valence electrons? What is that group’s special name?

Review Time! Which group is NONREACTIVE? Why?

Review time! Would Cesium react (have similar chemical properties) like Lithium or Barium? Why?

Review Time! A new element was found!!! They have named it Gonzalium…It has 113 protons. Which group would it be in? Which elements would have similar chemical and physical properties like Gonzalium?

What did we learn? C.5B: Use the Periodic Table to identify and explain the properties of chemical families, including alkali metals, alkaline earth metals, halogens, noble gases, and transition metals. C.5C: Use the Periodic Table to identify and explain periodic trends, including atomic ionic radii, electronegativity, and ionization energy. (BEGIN)

Exit Ticket: Explain why elements in the same group have similar chemical and physical properties. Make sure to use valance electrons and oxidation numbers when explaining.