Transcript Do Now - March 17, 2009 - stroh

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…
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Compounds (ionic and covalent)
Chemical formulas
Electronegativity, ionization energy, polarity
Naming compounds
Valence electrons continued
Lewis structures
• You will get to…
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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
Add to Vocabulary Log!
Water molecules
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 them
3. 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:
Add to Vocabulary Log!
– Ionic
– Covalent
Chemical Bond Spotlight: NaCl
(table salt)
Na
Cl
NaCl
2 different elements:
– Sodium (Na)
– Chlorine (Cl)
1 compound:
– Sodium chloride
(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.
Add to Vocabulary Log!
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
H 2O
Add to Vocabulary Log!
CO2
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) RATIO
– 1 atom C (carbon)
– 3 atoms O (oxygen) 2 Na : 1 C : 3
– 6 total atoms (2 + 1 + 3 = 6)
O
Chemical Formula Practice
• Determine the ratio of atoms in the
following compounds.
1.
2.
3.
4.
5.
6.
N2
CO
H2CO3
KOH
CaCO3
KNO3
Ionic Bond
• An ionic bond is a type of bond that
holds oppositely charged particles
together in an ionic compound
Add to Vocabulary Log!
Examples of ionic bonds
• Sodium chloride (NaCl)
• Barium chloride (BaCl2)
• Potassium fluoride (KF)
• Lithium bromide (LiBr)
What to know about
ionic bonds
1. Metal + Nonmetal
2. 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
Cl
Ca
Cl
Cl
Ca
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 STRONG
I’m ionic!
BOND!
Metal
Nonmetal
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 element
2. Subtract the smaller number from the
bigger number
Example: 4.0 (F) – 0.9 (Na) = 3.1
3. Look at Electronegativity Rules to
determine if it is ionic or not ionic
Electronegativity Rules
If electronegativity difference (DEN) is…
0 to 1.99: bond is not ionic
2.0 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
•
1.
2.
3.
4.
5.
Draw Lewis structures for the following
elements on the back of your notes
sheet
K
6. O
Be
7. Br
Al
8. Ar
C
9. He (there’s a trick!)
P
Exit Ticket
1. 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?