Do Now - March [22-5], 2009

1. Give three examples of things that involved nuclear chemistry.

2. What is the definition of a half-life?

3. Draw the basic shape of a half-life graph.

Agenda

• Do Now/Announcements• Welcome to Unit 4!• Quiz-Quiz-Trade• Vocabulary/Concepts Times Three!• Exit Ticket

Objectives

• SWBAT describe ionic compounds.• SWBAT determine if a bond is ionic

or not using electronegativity.• SWBAT draw Lewis structures 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 structures

• You will get to…– Quiz-Quiz-Trade!– Speed Date!– Investigate!– Show how much you know right before the

GEE!

Atom - the smallest particle of an of an element

What is a compound?

• A compound is a pure substance

• A compound is a combination of two or more different elements that are chemically combined

Water moleculesAdd to Vocabulary Log!

Familiar Compounds and Their Formulas

•Vinegar•Acetic acid•CH2COOH

Grain Alcohol•Ethanol

•C2H5OH

Cane sugar

•Sucrose

•C12H22O11

Stomach acid•Hydrochloric acid

•HCl

What is a compound?

• A compound is a pure substance

• A compound is a combination of two or more different elements that are chemically combined

• Remember! Electrons do all the work in chemical bonds!

• Atoms do 3 things with electrons:

1. Give them away

2. Take them3. Share them

What is a chemical bond?

• A chemical bond is the force that holds two atoms together in a compound (attractive force)

• There are two types main types of bonds:– Ionic –Covalent

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Chemical Bond Spotlight: NaCl (table salt)

2 different elements:– Sodium (Na) – Chlorine (Cl)

1 compound:– Sodium

chloride (NaCl)

Na Cl

NaCl

Chemical Bond Spotlight: NaCl (table salt)

Chemical Formula•A chemical formula is a

combination of chemical symbols used to represent a compound.

•A chemical formula contains the ratio of atoms for the compound.

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Ratio Examples• KBr has 1 atom of K and 1 atom of Br

– This means it has a ratio of 1 K : 1 Br

• H2O has 2 atoms of H and 1 atom of O

– This means it has a ratio of 2 H : 1 O

• CO2 has 1 atom of C and two atoms of O

– This means it has a ratio of 1 C : 2 O

Subscript Numbers•Subscript numbers are placed to the lower right of element symbols and are used to show how many atoms of each element are present

H2O CO2

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Chemical Formulas• What is a chemical formula?

• What is a subscript number?• What does the subscript number

tell us?If there is no number, it is an implied

ONE• Example: Na2CO3

– 2 atoms Na (sodium)– 1 atom C (carbon)– 3 atoms O (oxygen)– 6 total atoms (2 + 1 + 3 = 6)

RATIO

2 Na : 1 C : 3 O

Chemical Formula Practice

• Determine the ratio of atoms in the following compounds.

1. N2

2. CO3. H2CO3

4. KOH5. CaCO3

6. KNO3

Ionic Bond

• An ionic bond is a type of bond that holds oppositely charged particles together in an ionic compound

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Examples of ionic bonds

• Sodium chloride (NaCl)

• Barium chloride (BaCl2)

• Potassium fluoride (KF)• Lithium bromide (LiBr)

What to know aboutionic bonds

1. Metal + Nonmetal2. Metal gives electrons to nonmetal

Metal --> Cation; Nonmetal --> Anion This deals with ionization energy

• STRONG bonds!High melting and boiling points

• Exist in crystal lattice structures Usually hard, brittle solids

1. Conduct electricity when dissolved in water

2. Have large electronegativity differences

1. Metal vs. Nonmetal

Ca

Cl

CaCl

Cl

2. Ionization Energy• Ionization energy is the energy

required to remove one electron from an atom

• Trends:

3. STRONG Bonds

• STRONG bonds are hard to pull apart

• Ionic compounds want to stay together

I’m so STRONGI’m ionic!

Metal Nonmetal

BOND!

4. Crystal Lattice Structures

• Crystal lattice (solid) - atoms are arranged in an orderly, geometric, 3-D structure

• Hard: opposite of soft• Brittle: breakable

(think of rock candy)• Solid: describe this

state of matter

Na - Blue Cl - green

5. Conduct Electricity• Charged particles must be free to

move in order to conduct electricity• In solid state, ionic compounds do

not conduct electricity• However, in liquid state (dissolved in

water), they do conduct electricity– These are called electrolytes!– Electric Pickle!

6. Large Electronegativity

Differences• Electronegativity is an atom’s ability to attract electrons to itself in a chemical bond

• Electronegativity is expressed in numerical values of 4.0 or less– These numerical values are called

Paulings– Higher number means the atom will

attract electrons in a chemical bond

Electronegativity Trends

Pauling Values

How to Calculate Electronegativity Difference

(DEN)1.Look at Pauling values for each

element2.Subtract the smaller number from the

bigger numberExample: 4.0 (F) – 0.9 (Na) = 3.1

3.Look at Electronegativity Rules to determine if it is ionic or not ionic

Electronegativity RulesIf electronegativity difference (DEN) is…

0 to 1.99: bond is not ionic2.0 or greater: bond is ionic

DEN Practice

• Please work the problems in your notes.

Lewis Structures

1. Write the element symbol.2. Determine number of valence

electrons for that element.3. Draw dots to represent valence

electrons. Only pair dots up if they have to be paired!

H B Cl

Lewis Structures Practice

• Draw Lewis structures for the following elements on the back of your notes sheet

1. K 6. O2. Be 7. Br3. Al 8. Ar4. C 9. He (there’s a

trick!)5. P

Exit Ticket1. List three characteristics of ionic

bonds (things to know about ionic bonds).

2. Is the following compound ionic or not ionic? SO2

3. Draw the Lewis structure of nitrogen.

BONUS QUESTION! Why did the Electric Pickle light up?