section iv: moving electrons - newton public schoolspeter_hamel/612/notes/u1 l21 (10-31-14).pdf ·...

Section IV: Moving Electrons • Lesson 17 Technicolor Atoms • Lesson 18 Life on the Edge • Lesson 19 Noble Gas Envy • Lesson 20 Getting Connected • Lesson 21 Salty Eights • Lesson 22 Isn’t It Ionic? • Lesson 23 Alchemy of Paint • Lesson 24 Shell Game

Lesson 17: Technicolor Atoms

•Flame Tests

U1, L 17: Technicolor Atoms 10/17 •DQ: How can we get evidence that certain atoms are in a compound? •Please make a stack of PS 3 on the table for collection.

•ChemCatalyst: These drawings are models that show solid copper, solid copper chloride, and aqueous copper chloride as collections of atoms.

1. Describe each model.

2. What is similar about each model? What is different?

Cu(s)

Solid copper

CuCl2(s)

Solid copper (II) chloride

CuCl2(aq)

Aqueous copper (II) chloride

You will be able to:

• conduct a flame test and use the results to determine the identity of a compound

• interpret evidence of the presence of certain atoms within compounds

Prepare for the Lab •Work in groups.

•You will be using chemicals and fire today. Follow safety instructions.

•Wear safety goggles.

•Tie back long hair and remove dangling jewelry.

•Roll up long sleeves and keep clothing away from flames.

•Locate the eye wash, fire blanket, and fire extinguisher before starting the lab.

Lighting a Bunsen Burner 1) Make sure the area is clear and that you are properly

dressed (hair tied back, goggles on, etc.). 2) Make sure the burner is securely connected to the gas jet. 3) Close the “windows” at the bottom of the burner. 4) Light your match or lighter and hold it near the mouth of

the burner. 5) Slowly turn on gas. 6) Adjust flame height using the gas jet handle. 7) Adjust flame intensity using “windows” on the burner. 8) If it goes out at any point, immediately turn gas off. 9) NEVER LEAVE IT UNATTENDED!

Homework

• Correct PS 3 using the answer key on the website (will be posted by 2:00).

– Be sure to use a different color for corrections.

– Leave evidence of corrections on every question.

New Seats!

Resuming Lesson 17 •Which element appears to be responsible for flame color? (Use evidence.) •Would all elements produce a color?

Discussion Notes •Flame test: A test used in the laboratory to look for the presence of certain metal atoms. A sample of a compound is heated in a flame, and the resulting color is noted.

What evidence is there that Cu(NO3)2, CuCl2, and CuSO4 all contain Cu atoms?

What’s going on during flame tests? •Sodium Atom, Na

Wrap Up

•What evidence is there that certain atoms are present in a compound?

– Many metal atoms produce a characteristic colored flame when compounds containing those atoms are heated in a flame.

– Flame tests are evidence that elements and compounds are collections of atoms.

Lesson 18: Life on the Edge

•Valence and Core Electrons

U1, L18: Valence and Core e- DQ: Why do elements in the same group have similar properties?

ChemCatalyst:

1.What do you notice about the number of spokes on the circles?

2.The spokes represent electrons. Do the spokes represent the total number of electrons? Explain your thinking.

You will be able to:

• create a shell model diagram of an atom, placing the correct number of electrons in the correct shells

• explain the difference between a valence electron and a core electron

• describe the patterns in the periodic table associated with electron arrangements

Pre-Activity Notes • The shell model

• Each circle is called a

• Farther from nucleus =

Pre-Activity Notes •More examples of the shell model:

Pre-Activity Notes •In reality, shells are 3-dimensional

Definitions •Valence shell:

•Valence electrons:

•Core electrons:

Periodic Table and the Shell Model •Total # of electrons =

•# of shells with electron in them =

•# of valence electrons =

•# of core electrons =

Wrap Up •Why do elements in the same group in the periodic table have similar properties?

– Electrons occupy distinct areas around the nucleus called electron shells. The arrangement of electrons in these shells is highly predictable.

– For main group elements, elements in the same group have the same number of valence electrons.

– The number of valence electrons increases across a period.

– The number of shells and the number of core electrons increase as you go down a group.

Check-in •Provide each piece of information for element 34.

•a. The element’s name and symbol.

•b. The total number of electrons in an atom of this element.

•c. The number of core electrons in an atom of this element.

•d. The number of valence electrons.

•e. The group number for this element.

•f. The names of other elements with the same number of valence electrons.

U1, L18X: Electronegativity • DQ: What does the arrangement of electrons tell us about how

strongly the nucleus attracts them?

• ChemCatalyst: Below are shown three diagrams of a positive charge with a negative charge circling around it. Put the three in order from strongest to weakest attraction between the charges.

3 Key Things to Remember About Coulomb’s Law

1)

2)

3)

Effective Nuclear Charge (Zeff)

• Valence electrons are “shielded” from the nucleus by core electrons.

• Each core electron effectively “cancels” the charge of one proton.

• Zeff tells us the charge valence electrons “feel” attracting them to the nucleus.

Zeff Example

Lithium, Li

Complete the Worksheet

Top to Bottom Trend

• As you go from top to bottom in the P.T.

– Zeff

– Distance from nucleus

• Coulomb’s Law says

Left to Right Trend

• As you go from left to right in the P.T.

– Zeff

– Distance from nucleus

• Coulomb’s Law says

Electronegativity

Wrap-Up • What does the arrangement of electrons tell us

about how strongly the nucleus attracts them?

– Electronegativity measures how strongly the nucleus attracts valence electrons.

– Electronegativity increases toward the top right of the periodic table (except noble gases, which don’t make bonds).

Lesson 19: Noble Gas Envy

•Ions

U1, L19: Ions 10/28 • DQ: How can valence electrons and electronegativity be used to

predict the result of combining two elements?

• ChemCatalyst: When a lithium atom and a fluorine atom meet, one of them will steal an electron from the other.

1. Predict who takes the electron and who loses it.

2. What effect does the electron transfer have on the charge of each atom?

3. After electron transfer . . .

a) Li has the same number of electrons as what element?

b) F has the same number of electrons as what element?

You will be able to:

• explain that an ion is formed when an atom loses or gains electrons and state the difference between a cation and an anion

• determine the charge on an ion based on an atom’s placement in the periodic table

• explain the relationship between ion charge and valence electrons

Pre-Activity

• Ion = an atom (or group of atoms) that has a positive charge (because it lost one or more electrons) or a negative charge (because it gained one or more electrons.

• Cation = Positive ion (has lost electrons)

• Anion = Negative ion (has gained electrons)

Charges on ions are predictable

Representing Ions

“Lewis Dot” Representations of Atoms/Ions

Ions tend to “look like” noble gases.

The “Octet Rule” for Ionic Bonding

Wrap Up •How can valence electrons and electronegativity be used to predict the result of combining two elements?

– Nonmetal atoms are stronger at pulling electrons, so they tend to take electrons away from metal atoms.

– When atoms gain or lose electrons, they form ions. Ions are atoms that carry a net positive or net negative charge.

– When atoms lose electrons, they have a positive charge and are called cations.

– When atoms gain electrons, they have a negative charge and are called anions.

– Ions have electron arrangements resembling those of the noble gas atoms.

Check-in

1. Draw a shell model for calcium, Ca, showing the arrangement of its electrons.

2. What would have to happen for an atom of calcium to have an electron arrangement like that of a noble gas? Explain.

Lesson 20: Getting Connected

•Ionic Compounds

U1, L20: Ionic Compounds •DQ: How can valence electrons be used to predict chemical formulas?

•ChemCatalyst: Metal elements combine with the nonmetal element chlorine, Cl, to form compounds. The formulas are given in the tables.

1. Compare the three tables. What do you notice?

2. Predict the formula of a compound formed between lithium, Li, and chlorine, Cl. Which table would you put it in?

Element Compound

Na NaCl

K KCl

Element Compound

Mg MgCl2

Ca CaCl2

Element Compound

Ne none

Ar none

You will be able to:

• predict the chemical formulas of compounds that will form between metal and nonmetal atoms

• explain how an ionic compound forms and determine whether it follows the rule of zero charge

Pre-Activity Notes

Ionic compound =

Ionic Compound Example Mg2+ + Cl– + Cl– produces MgCl2 with zero charge.

Complete the Worksheet

Discussion Notes (cont.) •Metal and nonmetal elements combine to form ionic compounds.

•The electron arrangements of the cations and anions resemble the arrangements of a noble gas atom.

Discussion Notes (cont.)

•The rule of zero change can be used to determine the chemical formulas of ionic compounds.

•Rule of zero charge: In an ionic compound, the positive

charges on the metal cations and the negative charges on

the nonmetal anions sum to 0.

Examples of the rule of zero charge •Chemical Formulas of Ionic Compounds

Example

Number of

valence

electrons for the

metal

Number of

valence

electrons for

the nonmetal

Total

number of

valence

electrons

Total

positive

charge

Total

negative

charge

Total

charge

NaF 1 7 8 +1 –1 0

MgO 2 6 8 +2 –2 0

AlN 3 5 8 +3 –3 0

K2Se 1 6 8 2(+1) –2 0

MgCl2 2 7 16 +2 2(–1) 0

AlF2 3 7 24 +3 3(–1) 0

Al2O2 3 6 24 2(+3) 3(–2) 0

The Octet Rule Revisited

•The number of electrons associated with the atoms of an ionic compound generally totals 8 or a multiple of 8.

Wrap Up •How can valence electrons be used to predict chemical formulas?

– Metal atoms and nonmetal atoms combine to form ionic compounds.

– In ionic compounds, the metal is considered a cation, and the nonmetal is considered an anion.

– The charges on the cations and the anions in ionic compounds sum to 0.

– Metal atoms and nonmetal atoms usually combine in ratios that result in a total of eight valence electrons or a multiple of eight valence electrons.

Check-in What elements will combine with strontium, Sr,

in a 1:1 ratio? Explain your thinking.

Lesson 21: Salty Eights

•Formulas for Ionic Compounds

U1, L21: Salty Eights 10/31 • DQ: How can you predict

chemical formulas and name ionic compounds?

• Chemcatalyst: Find these cards in your Salty Eights card deck.

1. List the ionic compounds you can make with pairs of cards, using two different elements.

2. List the ionic compounds you can make with three cards and only two different elements.

3. What rule must all these compounds satisfy?

You will be able to:

• use valence electrons to predict ionic compounds

• develop proficiency at naming binary ionic compounds and writing their chemical formulas

Things to remember during the game

Discussion Notes

•In general, atoms come together to form an ionic compound if the number of valence electrons totals 8 or a multiple of 8.

Discussion Notes (cont.)

•Writing correct chemical formulas is a matter of keeping track of exactly how many atoms come together to make a compound.

•Creating correct chemical names is a matter of remembering some basic guidelines.

Wrap Up

•How can you predict chemical formulas and name ionic compounds?

– Ionic compounds tend to form from atoms that together have a total of 8 (or a multiple of 8) electrons in their outermost (valence) shells.

– Noble gases already have eight valence electrons and don’t combine with other elements to make new compounds. They are already highly stable.

Check-in Which of these compounds are likely to form?

a. Na2S b. K2Mg c. AlBr2

d. Na3N e. OCl f. CaO

Lesson 22: Isn’t It Ionic?

•Polyatomic Ions

ChemCatalyst

•The cards show a sodium ion and three polyatomic ions.

1. What do you think a polyatomic ion is?

2. Name three compounds formed between sodium ions and each of the three polyatomic ions. Use the rule of zero charge to write the compounds’ formulas.

Key Question

•What is a polyatomic ion?

You will be able to:

• recognize and name polyatomic ions

• write names and chemical formulas of compounds with polyatomic ions

Prepare for the Activity

•Work in pairs.

•Ionic compound: An ionic compound is a compound

composed of positive and negative ions, formed when

metal and nonmetal atoms combine.

Discussion Notes

•Polyatomic Ions

Discussion Notes (cont.)

•Polyatomic ions contain more than one atom.

•Most polyatomic ions are anions, with negative charges.

•Polyatomic ion: An ion composed of a group of

atoms with an overall positive or negative charge. Most polyatomic ions are anions.

Discussion Notes (cont.)

•The rule of zero charge can be used to predict the formulas of compounds that contain polyatomic ions.

Discussion Notes (cont.)

•Compounds containing polyatomic ions have their own

unique naming guidelines. Polyatomic ion Name

OH– hydroxide

NO3– nitrate

CO32– carbonate

SO42– sulfate

NH4+ ammonium

Wrap Up

• What is a polyatomic ion?

• Polyatomic ions are ions composed of a group of atoms. The charge is shared by all the atoms.

• To write the formula of an ionic compound that contains polyatomic ions, use the rule of zero charge.

• When naming compounds containing polyatomic ions, simply insert the name of the ion.

Check-in

1. What is the name of the compound Be(NO3)2?

2. What ions are present in this compound, and what are the charges on the ions?

Lesson 23: Alchemy of Paint

•Transition Metal Chemistry

ChemCatalyst

1. What types of substances will you be creating in today’s lab?

2. What safety precautions are especially important for today’s lab?

3. Describe one of the procedures you will be completing in class today.

Key Question

•What types of compounds are made from transition metals?

You will be able to:

• recognize transition metal compounds and their names

• determine the charge on transition metal ions given their chemical formula

Prepare for the Lab

•Work in groups of four.

•You will be working with transition metal compounds and acid. Follow lab safety guidelines.

– Wear safety goggles at all times.

– When heating compounds in a test tube, keep the open end pointed away from yourself and others.

– If any compound comes in contact with your skin, wash immediately with plenty of water.

– Tie back long hair and loose clothing. Remove any dangling jewelry.

Prepare for the Lab (cont.)

•To decant and filter a solid, fold filter paper following instructions.

Discussion Notes

•Many of the paint pigments that artists historically used and continue to use are ionic metal-nonmetal

compounds.

Wrap Up

•What types of compounds are made from transition metals?

– Many of the colorful pigments used in painting are formed from metal-nonmetal compounds with transition metal cations.

– Paint pigments in famous paintings can be as valuable as gold. A compound or element does not have to be gold to be valuable.

Lesson 24: Shell Game

•Electron Configurations

ChemCatalyst

•These drawings show two different ways to represent the arrangement of the electrons in atoms of the element calcium, Ca.

•1. Name at least two differences in the drawings.

•2. Name at least two similarities in the drawings.

Key Question

•What does the periodic table indicate about the arrangements of electrons?

You will be able to:

• describe the structure of an atom in terms of electron shells and subshells

• use the periodic table to determine the electron arrangement in an atom and to write electron configurations

• explain the organization of the periodic table in terms of the arrangements of electrons in subshells

Prepare for the Activity

•Work in pairs.

Discussion Notes

•The electron shells in the shell model of an atom (except for n = 1) are divided into subshells.

Shell Number of electrons in the shell Subshell Number of electrons in the subshell

n = 1 2 1s 2

n = 2 8

2s

2p

2

6

n = 3 18

3s

3p

3d

2

6

10

n = 4 32

4s

4p

4d

4f

2

6

10

14

Discussion Notes (cont.)

•In an electron configuration, the number indicates the shell number, the letter indicates the subshell within the shell, and the superscript indicates the number of electrons in the subshell.

•Electron configuration: A shorthand way to keep track of all the electrons in an atom of an element for all the subshells that have electrons. The number of electrons in each subshell is shown as a superscript.

Discussion Notes (cont.)

•The periodic table is organized in subshell blocks.

Discussion Notes (cont.)

•The order of filling subshells does not always correspond to the numerical order of the subshells.

•The elements in the different subshell blocks have related properties.

Wrap Up

•What does the periodic table indicate about the arrangements of electrons?

– Each electron shell in the shell model, except for n = 1, is divided into subshells.

– Each subshell can hold a specific maximum number of electrons.

– The periodic table can assist you in figuring out the placement of electrons in subshells.

– Chemists keep track of electrons and the subshells they are in by writing electron configurations.

Check-in

•Identify the element with this electron configuration:

•1s22s22p63s23p64s23d104p3