CHEMISTRY BELL RINGERIAN PG. Week of 11/16/2015 Tuesday 11/17/15 1.DEFINE VALENCE ELECTRONS. 2.HOW ARE THE NUMBER OF VALENCE ELECTRONS OF THE REPRESENTATIVE ELEMENTS DETERMINED? 3.DESCRIBE CATIONS. 4.DESCRIBE ANIONS.

7-1 IONS KEY CONCEPTS 1.How do you find the number of valence electrons in an atom of a representative element? 2.Which atoms tend to gain electrons? Lose? 3.How are cations formed? 4.How are anions formed? MAIN IDEAS 1.Valence Electrons 2.Electron Dot Structures 3.Octet Rule 4.Halide Ions IaN pg. Small deeds done are better than great deeds planned. -Peter Marshall

Ionic Bonds  The behavior of sodium…  Look at its electron configuration  Sodium = group IA = 1 valence electron  Valence electrons are the electrons in the highest occupied energy level of an element’s atoms.  Sodium wants to be like a noble gas.  At most, an atom can only gain or lose 3 electrons.  Sodium will lose 1 electron.

 Sodium now has the electron configuration of neon.  Is it neon? No. It still has 11 protons. It is isoelectronic with neon.  Now it looks like this: Na +

 The behavior of chlorine…  Look at its electron configuration  Chlorine = group 7A = 7 valence electrons  Chlorine wants to be like a noble gas.  At most, an atom can only gain or lose 3 electrons.  Chlorine will gain 1 electron.  Chlorine now has the electron configuration of a noble gas (argon).  Now it looks like this: Cl -

Ions  The transfer (or movement) of electrons produces ions.  Cations (Cat-ions) = ions with a positive charge.  Anions = ions with a negative charge.  Anions will usually end in –ide when naming them.

Opposites Attract  An ionic bond is a chemical bond that is formed from the attraction between a cation and an anion. This is an electrostatic attraction.  Ionic bonds form compounds that are usually called salts.  Salts typically have crystalline structures.

 Octet Rule – in forming compounds, atoms tend to achieve the electron configurations of noble gases.  Metals tend to lose electrons to achieve this.  Nonmetals tend to gain electrons to achieve this.  Some ions formed by transition metals do not have noble gas configurations and are exceptions to the octet rule – more on this later.  The electrical charge that an atom achieves (in trying to become more like a noble gas) is sometimes called its oxidation state.

CHEMISTRY BELL RINGERIAN PG. 26 Week of 11/16/2015 Wednesday 11/18/15 IONIC BONDING & LEWIS DOT DIAGRAMS

Putting Ions Together – Ionic Compounds  Ionic compounds must be neutral, which means the positive charge of the cation and the negative charge of the anion must balance each other.  Ex. NaCl = Na + and Cl - = a balanced charge.

 What if Mg and Br form a compound?  We want to know the formula unit. The formula unit is the lowest, whole number ratio of ions in an ionic compound.  1. Write the elements side by side with the metal on the left: Mg Br  2. Decide how to balance their charges: Mg 2+ Br 1-  3. Rewrite: MgBr 2

 How about Al and O?  1. Write the elements side by side with the metal on the left: Al O  2. Decide how to balance their charges: Al 3+ O 2-  3. Rewrite: Al 2 O 3

 Compounds made with polyatomic ions work the same way…  Combine NH 4 with S:  1. Write the elements side by side: NH 4 S  2. Decide how to balance their charges: NH 4 1+ S 2-  3. Rewrite: (NH 4 ) 2 S  Notice that the polyatomic needs to be in parenthesis before adding the subscript.

V. Lewis Dot Structures A. “Dot Models” used to represent Valence electrons B. Gilbert Newton Lewis American Chemist discovered covalent bond

Groups - Review Each column is called a “group” Each element in a group has the same number of electrons in their outer energy level. Except for He, it has 2 electrons The electrons in the outer energy levels are called “valence electrons”

1. Write the element symbol. 2. Locate the group (1 – 8) This is the # of valence electrons. 3. Follow this diagram for placing “Dots” in order. Copy this down C.Drawing Lewis Dot Structures

Assignment…  Practice problems # 1 & #2 pg. 193  Section Assessment #3-11 pg. 193