Catalyst – October (11+8), 2009 Monday Mystery Element!  Comes from the Latin word argentum  Found in its natural state  Used as a currency since Biblical times

Catalyst – October (11+8), 2009 Monday Mystery Element!  Comes from the Latin for argentum  Found in its natural state  Used as a currency since Biblical times

Today’s Agenda  Catalyst  Welcome to Unit 4!  Lewis Dot Structures  Octet Rule and Ions  Work Time  Exit Question

Today’s Objectives  SWBAT draw Lewis dot structures for atoms.  SWBAT predict the stable ion(s) that an atom will form when it reacts.  SWBAT determine oxidation number for atoms.

What to expect in Unit 4  You will learn about…  Compounds (ionic and covalent)  Chemical formulas  Electronegativity, ionization energy, polarity  Naming compounds  Valence electrons continued  Lewis dot structures  You will get to…  Quiz-Quiz-Trade!  Speed Date!

Atom - the smallest particle of an element

Why are compounds so important? Most substances in our world are compounds! They are everywhere!

Familiar Compounds and Their Formulas  Vinegar  Acetic acid  CH 2 COOH

Grain Alcohol  Ethanol  C 2 H 5 OH

Cane sugar  Sucrose  C 12 H 22 O 11

Stomach acid  Hydrochloric acid  HCl

What is a compound? Key Point #1: A compound results from interaction between valence electrons of different atoms

Interaction of Valence Electrons Key Point #2: Atoms will either take, give, or share electrons.  These different electron behaviors determine the types of bonds formed between atoms.

Chemical Bond Spotlight: NaCl (table salt) 2 different elements:  Sodium (Na)  Chlorine (Cl) 1 compound:  Sodium chloride (NaCl) NaCl NaCl

Chemical Bond Spotlight: NaCl (table salt) Let’s see a video!

Chemical Spotlight: H 2 O (water)

How can we “see” bonds happen? Key Point #3: Lewis dot structures show the valence electrons of an atom.

How do you draw a Lewis Dot Structure?  Use the following examples and what you know about valence electrons to figure out how to draw the remaining Lewis dot structures: HLiNeNBe Try these! O, Br, Al

Rules for Drawing Lewis Dot Structures 1. Write the element symbol. 2. Pretend there is a box around the element symbol. 3. Draw one dot for each valence electron in the atom. 4. Do not pair up dots unless you have to! (after 4)

Lewis Dot Sructures What do the Lewis dot structures have in common?!?!?

Lewis Dot Structure Practice  Draw the Lewis dot structures (LDS) for the following elements: 1. Calcium (Ca)4. Krypton (Kr) 2. Gallium (Ga)5. Sodium (Na) 3. Phosphorus (P)6. Selenium (Se) Question: Why haven’t we drawn any LDS’ for transition metals?

LDS Practice Review 1. Ca4.Kr 2.Ga5.Na 3.P6.Se Question: Why haven’t we drawn any LDS’ for transition metals?

First thing you need to know about ionic bonds…. Key Point #4: Ionic bonds are formed when oppositely charged ions are attracted to each other  Positive ions are called CATIONS  Negative ions are called ANIONS + -

Some questions to think about… 1. What kind of charge does an electron have? (-1) 2. What kind of charge does an entire atom have? Neutral (positives = negatives) Think to yourself: If an atom gains an electron, what kind of charge will it have? What about if an atom loses an electron???

Formation of Ions  An ion is an atom that has lost or gained an electron(s)

Formation of Positive Ions (CATIONS)  Imagine that electrons are pieces of poop  Is poop in your yard (an atom’s energy levels) a positive or negative thing?  So…if you get rid of the poop in your yard, are you more positive or more negative? + So…POSITIVE ions are formed when an atom LOSES one or more electrons!

Formation of Negative Ions (ANIONS)  Again, imagine that electrons are pieces of poop  Is poop is flying into your yard (an atom’s energy levels) a positive or negative thing?  So…if poop lands in your yard, are you more positive or more negative? So…NEGATIVE ions are formed when an atom GAINS one or more electrons! -

Practice Questions 1. If an atom gains an electron it will have a ___________ charge. 2. If an atom loses an electron it will have a ___________ charge. 3. If chlorine gains 3 electrons it will have a _______ charge. NEGATIVE POSITIVE 3-

Types of Ions Recap  Cation– a positive ion (+)  “t” looks like (+)  Anion– a negative ion (-)  “n” for negative + -

Ion Properties S gains 2 electrons

Ion Properties S 2- This is called the OXIDATION NUMBER – the CHARGE of an ion

Ion Properties Co loses 2 electrons

Ion Properties Co 2+ What is the oxidation number?

Ion Properties Co 2+ What is the oxidation number? 2+

Ion Properties Si 3- What is the oxidation number?

Ion Properties Si 3- What is the oxidation number? 3-

Ion Properties Si 3- Silicon has gained 3 electrons. How many electrons does Si have now?

Ion Properties Si 3- Silicon has gained 3 electrons. How many electrons does Si have now? 17

Practice Problems Do these in your notes! 1. Write down what ion will form for the following:  Sr gains 5 electrons  Phosphorous gains 1 electron 2. How many total electrons do the following ions have?  Cl 1-  Ca 2+  Ga 3+  O 1-  Zn 4+

How many electrons do atoms lose or gain? Is it all arbitrary? NO! Key Point #5: The octet rule helps us predict what type of ion an atom will form.

Octet Rule  What is different about the valence shells of the elements on the LEFT and those on the RIGHT?  The noble gases have full valence shells, the other atoms do not…

Octet Rule  The octet rule states that atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons.  Elements are most stable (happiest) when they have the electron configuration of a noble gas

Octet Rule  Atoms can either gain or lose electrons in order to become stable (happy)  Atoms with 5 or more valence electrons will gain electrons to be stable (happy)  Atoms with 3 or less valence electrons will LOSE electrons to be stable (happy)  How many electrons will the following atoms gain or lose to become stable (happy)?  F  O  H  N

Predicting Ions Practice  What is the STABLE ion that will form for the following elements?  P  Kr  Ca  I  K

Independent Practice Time! Please work on the worksheet. Ask questions if you have them!

Exit Question 1. What is the difference between an anion and a cation? 2. What is the stable ion that will form for the following elements? Write down the ion and how many electrons the atom will have total.  Lead  Te  Li

Terms to know  Compound  Chemical bond  Valence electron  Chemical formula  Lewis dot structure (electron-dot structure)  Ion  Oxidation number  Cation  Anion  Octet rule

Ionic Radius of Cations What happens to the RADIUS of the atom when it becomes a CATION? Does it get bigger or smaller?

Ionic Radius of Anions What happens to the RADIUS of the atom when it becomes a ANION? Does it get bigger or smaller?