Section IV: Moving Electrons

Lesson 17 Technicolor AtomsLesson 18 Life on the EdgeLesson 19 Noble Gas EnvyLesson 20 Getting ConnectedLesson 21 Salty EightsLesson 22 Isn’t It Ionic?Lesson 23 Alchemy of PaintLesson 24 Shell Game

Lesson 17: Technicolor Atoms

Flame Tests

Lesson 17: 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

Lesson 17: Key Question

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

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.

Discussion Notes

The metal element in each chemical formula appears to be responsible for the flame colors.

Only certain elements produce colorful flames.

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.

Discussion Notes (cont.)

Elements and compounds are collections of atoms.

The only way to change one atom into another is to change the nucleus through a nuclear reaction.

Discussion Notes (cont.)

Sodium Atom, Na

Discussion Notes (cont.)

The illustration indicates that the flame colors are associated with movements of the electrons within the sodium atom.

Bohr’s model of the atom came directly from evidence similar to that produced in class today.

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 17: Check-in

Predict the flame colors produced when heating these substances. Explain your thinking.• copper (II) carbonate• calcium chloride

Lesson 18: Life on the Edge

Valence and Core Electrons

Lesson 18: ChemCatalyst1. 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.

Lesson 18: Key Question

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

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

Prepare for the Activity

Work in pairs.

Prepare for the Activity (cont.)

The Shell Model

The surface of each sphere represents an area where an electronor a group of electronsis most likely to be found.

Prepare for the Activity (cont.)

Electron shells are the levels around the nucleus where electrons can be found.

Sodium and magnesium have electrons in three electron shells.

Discussion Notes

The atomic number of an element is the same as the total number of electrons.

The period (row) number of the element is the same as the number of electron shells.

For main-group elements, the group number of the element is the same as the number of electrons in the outermost shell.

Discussion Notes (cont.)Table of Valence and Core Electrons

Discussion Notes (cont.)

Valence shell: The outermost electron shell in an atom.

Valence electrons: The electrons located in the outermost electron shell of an atom.

Core electrons: All other electrons in an atom besides the valence electrons.

Discussion Notes (cont.)

The arrangement of electrons in their shells is highly predictable.

The numbers of core electrons also exhibit patterns across each row of the periodic table.

Wrap UpWhy 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.

Lesson 18: 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.

Lesson 19: Noble Gas Envy

Ions

Key QuestionHow is chemical stability related to the arrangements of electrons in atoms?

Lesson 19: ChemCatalystChemists have found that metal atoms transfer electrons to nonmetal atoms when they form compounds. Examine the shell model showing how a lithium atom might transfer an electron to a fluorine atom.

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

2. What element does each atom resemble after the electron has been transferred?

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

Prepare for the Activity

Work in groups of eight.

Ion: An atom (or group of atoms) that has a positive or negative charge because it has lost or gained electrons.

Discussion NotesThe table of arranged ion cards shows that charges on ions are quite predictable.

Discussion Notes (cont.)

When electrons are removed from or added to an atom, the rest of the atom stays the same.

The charge on an ion is noted with a superscript.

Discussion Notes (cont.)

Cation: An ion with a net positive charge. Usually these are formed from metal atoms.

Anion: An ion with a net negative charge. Usually these are formed from nonmetal atoms.

Discussion Notes (cont.)

Electron arrangementsof atoms in ioniccompounds resemblenoble gases.

Discussion Notes (cont.)

Atoms tend to lose or gain electrons to attain the electron arrangement of a noble gas.

Wrap Up

How is chemical stability related to the arrangements of electrons in 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.

Lesson 19: 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

Key QuestionHow can valence electrons be used to predict chemical formulas?

ChemCatalystMetal 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

Prepare for the ActivityWork 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

Mg2+ + Cl– + Cl– produces MgCl2 with zero charge.

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.

Discussion Notes (cont.)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

Al2O3 3 6 24 2(+3) 3(–2) 0

Discussion Notes (cont.)

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

Wrap UpHow 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.

Lesson 20 Check-inWhat elements will combine with strontium, Sr, in a 1:1 ratio? Explain your thinking.

Also, make sure you have these definitions in your notebook:

Ionic Compound - An ionic compound is a compound composed of positive and negative ions, formed when metal and nonmetal atoms combine.

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.

Lesson 21: Salty Eights

Formulas for Ionic Compounds

Key QuestionHow can you predict chemical formulas and name ionic compounds?

Lesson 21 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?

Lesson 21 ChemCatalyst # 2Find the Mg, magnesium, card.

Find the P, phosphorous, card.

(use whole deck to make compounds)

1. What group is Mg in?How many electrons does Mg have in its outer shell?What is the charge on the Mg ion?List at least 4 compounds that Mg can make with cards in the deck.

2. What group is P in?How many electrons does P have in its outer shell?What is the charge on the P ion?List at least 4 compounds that P can make with cards in the deck.

Goals of “Salty Eights” card game

• To make compounds and be the first to play all your cards.

• The compounds can be made of any number of cards, but no more than two different elements.

You will be able to:

• use valence electrons to predict ionic compounds

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

Prepare for the Activity

Work in groups of four (three).

Rules of “Salty Eights”

• Shuffle and deal eight cards to each player and place the rest in a draw pile. The player to the left of the dealer starts.

• When it’s your turn, put down a compound in front of you. Your compound must contain a metal card (gives away electrons) and a nonmetal (gains electrons) card, and the total valence electrons must add up to 8 or a multiple of 8. If you can’t play a compound, you can put down a noble gas (already 8 valence electrons).

Rules of “Salty Eights” (continued)

• Wild Cards can be used as any element in that particular group. You must identify which element a Wild Card represents at the time you use it.

• If you can’t make a compound, draw cards until you can play a compound or noble gas.

• When you play a compound, you must name it. Fill in the table. Your turn is over.

• Play until one player uses up all of his or her cards. Total your points for this 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.

Lesson 21 Wrap Up & CheckinHow 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) shell.

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

Explain 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

Key QuestionWhat is a polyatomic ion?

Lesson 22: ChemCatalystThe 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.

Lesson 22: 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.

Lesson 22: Discussion Notes

Polyatomic Ions Compound with Polyatomic Ions

Ammonium Nitrate Magnesium hydroxide

Discussion Notes (cont.)• Polyatomic ions contain more than one atom.• Most polyatomic ions are anions, with negative

charges.• The rule of zero charge can be used to predict

the formulas of compounds that contain polyatomic ions

Polyatomic ion: An ion composed of a group of atoms with an overall positive or negative charge. Most polyatomic ions are anions (negative charge).

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

Lesson 22: Wrap UpWhat is a polyatomic ion?• Polyatomic ions are ions composed of a group of

atoms. The charge is not zero, and 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.

Lesson 22: Check-in1. 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

Key QuestionWhat types of compounds are made from transition metals?

Lesson 23: 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.

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

Key QuestionWhat does the periodic table indicate about the arrangements of electrons?

Lesson 24: ChemCatalystThese 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.

Lesson 24: 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 24

Work in pairs.

Lesson 24: 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 183s3p3d

26

10

n = 4 32

4s4p4d4f

26

1014

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.

Lesson 24: Wrap Up What does the periodic table tell us about arranging the 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.

Lesson 24: Check-inIdentify the element with this electron configuration:

1s22s22p63s23p64s23d104p3