SAMPLE - Region 4 Service Center STAAR Grade 8 Sample Lesson w… · group prior to class. Teacher Instruction ... SAMPLE. Matter and Energy. Advance Preparation • • • • •

Grade 8

xx

Gateways to Science FeaturesINTRODUCTION to Gateways

Learning Goalprovides a brief outlook of lesson purpose.

Advance Preparationallows for preplanning to ensure lesson goes smoothly.

Safety Alert Iconreminds teacher and students of safe lab practices.

Lab Rotation Iconsignals students to prepare for lab station activities.

Station Descriptorssummarize for students lab activities by station.

Materials Listaids in lesson preparation.

5 Esare clearly labeled to help keep track of lesson progress.

ROTAT

ION

Stations

150

UNIT 2: Matter and EnergyLesson 11: Law of Conservation of Mass

EngagePage 82

Building Blocks

1. Arrange the objects in the plastic bag to model the reactants in the following equation.

NaOH + HCl NaCl + H2O

Notice that each color represents a different element in the equation.

Keyred = sodium

blue = hydrogen

yellow = oxygen

green = chlorine

2. Place all the reactant pieces on a balance to determine their mass. In your science notebook, record the mass.

Learning GoalDetermine if a chemical equation is balanced and how that relates to the law of conservation of mass.

Engage

Advance Preparation

• Gather the centigram cubes and place the correct amount in a resealable plastic bag for each group prior to class.

Teacher Instruction

• Distribute a plastic bag of centigram cubes to each group.

• Instruct students to follow the directions to complete the Engage activity and the science notebook entry.

Teacher Note• Centigram cubes can

be purchased from most educational supply companies. Many math departments use centigram cubes.

• Certain types of plastic such as toy building blocks or paper clips could be used instead of the centigram cubes, but the mass of individual blocks or paper clips may not be standardized.

MaterialsFor student groups• 1 red centigram

cube• 2 blue centigram

cubes• 1 yellow

centigram cube• 1 green

centigram cube • resealable

plastic bags• balance

1

SAMPLE

xxi© REGION 4 EDUCATION SERVICE CENTER. ALL RIGHTS RESERVED.

Gateways to Science Features

Science Notebook Icon quickly indicates the need for students to use a science notebook.

Facilitation Questionsassist in guiding and scaffolding instruction.

Reproducible Master (RM) Snapshots and Answer Keysoffer an at-a-glance view. RM Answer Keys are placed in lesson to reduce the amount of printed materials.

Teacher Noteprovides helpful tips and information.

Student Pagesare embedded in all lessons for ease of use and include answers to student edition.

157© REGION 4 EDUCATION SERVICE CENTER. ALL RIGHTS RESERVED.

Unit 2: M

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Figure 2.41. Engage Equation Model

NaOHsodium

hydroxide+

HClhydrochloric

acid

NaClsodium chloride

+H2O

water

Na O H + ClH Na Cl +H H

O

Science

100 Sheets • 200 Pages • Wide Ruled

9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Reflection

How are the activities in Explore similar to Figure 2.41?

Facilitation Questions

• What is the law of conservation of mass? Matter cannot be created or destroyed. The numbers of atoms in the reactants and the products are the same, but they are rearranged chemically.

• How does the Engage activity support the law of conservation of mass? The number of atoms in the reactants and products are the same. The mass of the reactants and the products are equal.

• How do the Explore activities support the law of conservation of mass? The mass of the reactants and products did not change.

Explain, Part 3

Teacher Instruction

• Read and discuss “Applying the Law of Conservation of Mass” to help students understand how to determine whether an equation is balanced or unbalanced.

• Display RM 60: ERP to model an example. Then guide students through several examples before releasing students to work independently. Allow students to compare, discuss, and revise their work in small-group settings.

• Instruct students to revisit their equations from Lesson 9, Elaborate, and identify which equations are balanced and which are not.

Teacher Note• Students should not

balance equations. Students only need to recognize whether an equation is balanced; this relates to the law of conservation of mass. Having students balance equations now is counterproductive to learning and can actually develop student misconceptions.

• Coloring the elements, coefficients, and subscripts with different colored map pencils prior to ERP (Elements, Reactant, Product) may help students identify important parts of the equation that could easily be missed.

MaterialsFor teacher• RM 60

© REGION 4 EDUCATION SERVICE CENTER. ALL RIGHTS RESERVED.

Gateways to Science, STAAR Edition, Grade 8 Page 1 of 2

ERP

UNIT 2: Matter and Energy RM 60Lesson 11: Law of Conservation of Mass

C + O2 CO2

C + O O OO C

reactants product

Elements Found in Equation

Reactant Atoms

(number of)

Product Atoms

(number of)

Lesson 11: Law of Conservation of Mass

128

UNIT 2: Matter and EnergyLesson 8: Analyzing Chemical Formulas

Evaluate

Teacher Instruction

• Instruct students to use the Periodic Table to complete RM 46: Assessment—Analyzing Chemical Formulas.

RM 46 Answer Key

1. D

2. G

3. D

4. F

5. A

MaterialsFor each student• RM 1• RM 46

RM 46 Answer Key


Gateways to Science, STAAR Edition, Grade 8

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Choose the best answer for each question.

1 Which element is found in all of these compounds?

C2H6 NaHCO3 C6H12O6 CO2

A Oxygen

B Sodium

C Hydrogen

D Carbon

2 How many atoms of carbon are found in glucose, C6H12O6?

F 3

G 6

H 12

J 24

3 A molecule that contains two or more elements is called —

A an atom

B a mixture

C an ion

D a compound

Assessment—Analyzing Chemical Formulas

UNIT 2: Matter and Energy RM 46Lesson 8: Analyzing Chemical Formulas

SAMPLE


Unit 2: M

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Lesson 8: Analyzing Chemical Formulas

EngagePage 64

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Which Does Not Belong?

In your science notebook, copy the list below. Circle the one word that does not belong in the group. Finish the statement that explains why it does not belong.

1. silver, nickel, cobalt, iron (not in period 4)

2. neon, nitrogen, helium, argon (not a noble gas)

3. group, period, seven, horizontal rows (not related to the horizontal rows on the Periodic Table)

4. vertical column, group, period, valence electrons (not related to the vertical columns on the Periodic Table)

5. sodium chloride, carbon dioxide, lead, lithium sulfide (not a compound; only has 1 element listed)

6. Cu, Ag, H2O, Au (not an element; has 2 elements listed; not a metal)

7. CH4, NaOH, C6H6, C6H12O6 (not an organic compound; does not contain carbon)

Learning GoalDetermine the number of atoms of each element in chemical formulas.

Engage

Teacher Instruction

• Instruct students to copy Items 1–7 in Engage into their science notebooks, circle the one word that does not belong in each list, and explain why it does not belong. Review the example in the student edition if necessary.

Teacher NoteItems 5 and 7 check students’ prior knowledge. A complete understanding of the concept is not expected at this time. The concept will be further developed in this lesson.SAMPLE

118


Explore

Advance Preparation

• Copy RM 40: Matching Cards in color on cardstock. Laminate, cut out, and place in plastic bags.

Teacher Instruction

• Instruct students to use the materials in the plastic bag to complete the Explore activity.

• Circulate among the working groups while making formative assessments and redirecting student thinking as needed.

• Allow students to participate in a gallery walk to compare results.

• Allow students to return cards to plastic bag after the Explain discussion.

ExplorePage 64

Matching Game

Working in small groups, match the graphic card model with a possible chemical formula.

RM 40 Answer Key

Refer to RM 40 for correct placement of cards.

MaterialsFor student pairs• RM 40• sandwich-size

resealable plastic bag



Matching Cards


SAMPLE



Unit 2: M

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Explain, Part 1

Teacher Instruction

• Debrief Explore by guiding students to recognize the relationships between the chemical formulas and the graphic cards.

• Guide students to recognize that the letters represent certain shapes and the number of shapes is equivalent to the subscript.

• Ask students to determine the total number of shapes in each graphic card. Later in the lesson, relate this number to the total number of atoms in a compound.

Explain, Part 2

Teacher Instruction

• Instruct students to read and discuss “Analyzing Chemical Formulas.”

• Display RM 41: Practice—Determining Atoms to model how to determine the atoms per element in a compound.

• Scaffold instruction by modeling several examples first. Use guided practice before students begin to work independently.

• Provide time for students to re-examine their Explore results, allowing revisions. Ensure answers are correct before students disassemble the materials and store them in the plastic bag.

• Instruct student pairs to complete the “Atoms per Element” science notebook entry.

• Review the answers with students, allowing them to revise their answers based on the class discussion.

• Extension Activity: If students are having difficulty determining the number of elements found in a compound or the number of atoms in each element, utilize RM 42: Additional Practice for remediation or additional practice

Explain, Part 1Page 65

Review the Explore card matching activity in a class discussion.

• What do the letters represent?

• What is the total number of shapes on each card?

MaterialsFor student pairs• Matching Cards

arrangement

MaterialsFor teacher• RM 41 • RM 42 (optional)

For each student• RM 41 (optional)• RM 42 (optional)

For student pairs• Matching Cards

arrangement



NaCl CH4

Fe2O3 H2SO4

HCl Mg(OH)2

Practice—Determining Atoms


Pb

O

O

O

N

N

N

C

O

O

OCaSAMPLE

120


Explain, Part 2Pages 65–66

Analyzing Chemical Formulas

All compounds have definite compositions that can be represented by a chemical formula. Remember that chemical formulas use symbols or a combination of symbols and subscripts to show the elements and the number of atoms of each element that make up the molecule.

For example, the formula for oxygen gas is O2. The subscript indicates two oxygen atoms are bonded in an oxygen molecule as shown in Figure 2.32.

Figure 2.32. Oxygen Molecule

O O

Another common chemical formula is H2O. As shown in Figure 2.33, H2 represents 2 atoms of hydrogen and O represents 1 atom of oxygen. H2O is the chemical formula for the inorganic compound known as water.

Figure 2.33. Molecule of Water

H H

O

The inorganic compound magnesium hydroxide is written as Mg(OH)2. Notice the subscript after the parentheses in Figure 2.34. The subscript indicates there are 2 sets of the OH molecule.

Chemical formulas are a shorthand way to communicate the parts of a molecule. Subscripts are used in formulas to identify how many atoms of a particular element are present. In some cases, parentheses are used to indicate elements grouped together as a molecule within the compound.

Figure 2.34. Magnesium Hydroxide

Mg(OH)2

H HO OMg



1. bromine—Br2

2. calcium chloride—CaCl2

3. potassium iodide—KI

4. benzene—C6H6

5. beryllium hydroxide—Be(OH)2

6. copper carbonate—CuCO3

7. magnesium nitrate—Mg(NO3)2

8. magnesium hydroxide—Mg(OH)2

9. silver oxide—Ag2O

10. ammonium hydroxide—NH4OH

11. sodium carbonate—Na2CO3

12. calcium nitrite —Ca(NO2)2

Additional Practice


SAMPLE



Unit 2: M

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Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Atoms per Element

Identify the elements found in each of the following compounds. Then determine the number of atoms in each element.

1. carbon dioxide—CO2

• 1 atom of carbon

• 2 atoms of oxygen

2. glucose—C6H12O6

• 6 atoms of carbon

• 12 atoms of hydrogen


3. calcium hydroxide—Ca(OH)2

• 1 atom of calcium

• 1 x 2 = 2 atoms of oxygen

• 1 x 2 = 2 atoms of hydrogen

RM 41 Answer Key

CaCO3 Pb(NO)3

NaCl CH4

1 atom of sodium1 atom of chlorine

1 atom of carbon4 atoms of hydrogen

Fe2O3 H2SO4

2 atoms of iron3 atoms of oxygen

2 atoms of hydrogen1 atom of sulfur4 atoms of oxygen

HCl Mg(OH)2

1 atom of hydrogen1 atom of chlorine

1 atom of magnesium2 atoms of oxygen2 atoms of hydrogen

SAMPLE

122


RM 42 Answer Key

1. bromine—Br2

• Molecule (not a compound) —1 element

• 2 atoms of bromine

2. calcium chloride—CaCl2

• compound—2 elements


• 2 atoms of chlorine

3. potassium iodide—KI


• 1 atom of potassium

• 1 atom of iodine

4. benzene—C6H6


• 6 atoms of carbon


5. beryllium hydroxide—Be(OH)2


• 1 atom of beryllium



6. copper carbonate—CuCO3


• 1 atom of copper



7. magnesium nitrate—Mg(NO3)2


• 1 atom of magnesium

• 2 atoms of nitrogen


8. magnesium hydroxide Mg(OH)2


• 1 atom of magnesium



9. silver oxide Ag2O


• 2 atoms of silver

• 1 atom of oxygen

10. ammonium hydroxide NH4OH


• 1 atom of nitrogen


• 1 atom of oxygen

11. sodium carbonate Na2CO3


• 2 atoms of sodium



12. calcium nitrite Ca(NO2)2



• 2 atoms of nitrogen


SAMPLE



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Explain, Part 3

Teacher Instruction

• Read and discuss “Using Coefficients and Subscripts.”

• Display RM 43: Using Coefficients to model how to determine the number of atoms in compounds with coefficients. Scaffold student instruction and involvement as described in previous lessons.

• Check for understanding by directing students to complete the science notebook entry “Chemical Formulas.”

• Display RM 44: Chemical Formulas to discuss the answers after students have had ample time to respond.

• Allow students to revise their answers after discussion.

Explain, Part 3Pages 67–68

Using Coefficients and Subscripts

A coefficient indicates the number of molecules of a compound or element. For example, 6 molecules of water is written as 6H2O.

Figure 2.35. Parts of a Compound

6H2OCoefficient—There are 6 molecules of water.

Subscript—There are 2 atoms of hydrogen in each of the 6 molecules of water.

No subscript—There is only 1 atom of oxygen in each of the 6 molecules of water.

A visual can also be used to help determine the total number of atoms. The coefficient indicates there are 6 molecules of water.

MaterialsFor teacher• RM 43• RM 44



Using Coefficients

UNIT 2: Matter and Energy RM 43

6H2O

3CaCl2

Coefficient —There are 6 molecules of water.


Subscript—There are 2 atoms of hydrogen.

No subscript—There is only 1 atom of oxygen.



Chemical Formulas


1. HO

2. HO

3. CHCl

4. 3CO2

5. 2CaSO3

6. 2 Ca(OH)2


H HO O

H H

O

H H

O

H H

O

C Cl

H

H

H C Cl

H

H

HSAMPLE

124


Figure 2.36. Visual Model of a Compound

H H

OH H

O

H H

OH H

O

H H

OH H

O

Here’s another way to determine the number of atoms of each element:.

To determine the number of atoms in 6H2O:

6 molecules x 2 hydrogen atoms = 12 hydrogen atoms

6 molecules x 1 oxygen atom = 6 oxygen atoms

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Chemical Formulas

In your science notebook, write the chemical formula for each of the following. Place the proper coefficient in the blank and any subscripts needed in the appropriate boxes.

1. H

O

3H2O

2. H

O

H2O2

3. C

H

Cl

2CH3Cl

H HO O

H H

O

H H

O

H H

O

C Cl

H

H

H C Cl

H

H

H

SAMPLE



Unit 2: M

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Copy the following formulas into your science notebook. Determine the number of atoms per element represented in each of the following substances. Justify your answers mathematically or with a drawing.

4. 3CO2

3 x 1 carbon = 3 atoms3 x 2 oxygen = 6 atoms

5. 2CaSO3

2 x 1 calcium = 2 atoms2 x 1 sulfur = 2 atoms2 x 3 oxygen = 6 atoms

6. 2Ca(OH)2

2 x 1 calcium = 2 atoms2 x (1 x 2) oxygen = 4 atoms2 x (1 x 2) hydrogen = 4 atom

Facilitation Questions

• What is a coefficient and what does it tell you? A coefficient is a number written in front of a chemical formula indicating how many of those molecules are involved in a chemical reaction.

• What is a subscript and what does it tell you? A subscript is a number within a chemical formula indicating the number of atoms of an element in that molecule.

SAMPLE

126


Elaborate

Teacher Instruction

• Instruct students to complete RM 45: Composition of Compounds.

• Once completed, utilize RM 45 to discuss student answers. Allow students to revise answers after discussion.

• Instruct students to complete the science notebook entry “Reflection.”

• Allow students to share their reflections and to revise if needed.

ElaboratePage 69

Follow your teacher’s instructions to complete the Composition of Compounds handout.

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Reflection

A friend is having difficulty writing chemical formulas. Create a list of guidelines to help your friend write chemical formulas. Student answers will vary. Possible answers may include: The first letter of an element symbol is always capitalized and the second letter is written lower case. Subscripts are used when there are two or more atoms of the element and are written to the lower right of the element. Subscripts are not used if only one atom of an element is present.

MaterialsFor teacher• RM 45

For each student• RM 45



Mo

del

Nam

eE

lem

ent,

Mo

lecu

le,

Co

mp

ou

nd

Fo

rmu

laTo

tal N

um

ber

o

f E

lem

ents

Nam

es o

f E

lem

ents

Nu

mb

er

of

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ms

of

Eac

h

Ele

men

t

HH

Ow

ater

H2O

HO

Na

sodi

um

hydr

oxid

e

Na

1 va

lenc

eel

ectr

on

CI

7 va

lenc

eel

ectr

ons

sodi

um

chlo

ride

(sal

t)N

aCI

Ca

2 va

lenc

eel

ectr

ons

CI

7 va

lenc

eel

ectr

ons

CI

7 va

lenc

eel

ectr

ons

calc

ium

ch

lorid

e

Mg

2 va

lenc

eel

ectr

ons

O

6 va

lenc

eel

ectr

ons

mag

nesi

um

oxid

e


Composition of Compounds


SAMPLE



Unit 2: M

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RM 45 Answer Key

Model NameElement, Molecule,

CompoundFormula

Total Number

of Elements

Names of Elements

Number of Atoms of Each Element

H H

Owater compound H2O 2

hydrogenoxygen

H = 2 atomsO = 1 atom

HONa sodium hydroxide

compound and molecule

NaOH 3sodiumoxygen

hydrogen

Na = 1 atomO = 1 atomH = 1 atom

Na

1 valenceelectron

CI

7 valenceelectrons

sodium chloride

(salt)compound NaCI 2

sodiumchlorine

Na = 1 atomCl = 1 atom

Ca

2 valenceelectrons

CI

7 valenceelectrons

CI

7 valenceelectrons

calcium chloride

compound CaCl2 2calciumchlorine

Ca = 1 atomCl = 2 atoms

Mg

2 valenceelectrons

O

6 valenceelectrons

magnesiumoxide

compound MgO 2magnesium

oxygenMg = 1 atomO = 1 atom

SAMPLE

128


Evaluate

Teacher Instruction

• Instruct students to use the Periodic Table to complete RM 46: Assessment—Analyzing Chemical Formulas.

RM 46 Answer Key

1. D

2. G

3. D

4. F

5. A

MaterialsFor each student• RM 1• RM 46



Lesson 1: Properties of MatterUNIT 2: Matter and Energy RM 1

PE

RIO

DIC

TA

BL

E O

F T

HE

EL

EM

EN

TS

12 2B

13 3A14 4A

15 5A16 6A

17 7A

18 8A

1011 1B

He

Hg

CdZn

Au

Ag

Cu

PtPdNi

TlGa

PbSnGe

Bi

SbAs

PoTeSe

At

Br

RnXeKr

Al

SiP

SC

lA

r

BC

NO

FN

e

Yb No

Tm Md

Er Fm

Ho Es

Dy Cf

Tb Bk

Gd

Cm

Eu Am

Mas

s nu

mbe

rs in

par

enth

eses

are

thos

e of

the

mos

t sta

ble

or m

ost c

omm

on is

otop

e.

Si

Sili

con

14

Sym

bol

Ato

mic

num

ber

Nam

e

28.0

86A

tom

ic m

ass

InI

KC

a

Na

Mg

LiB

e2 2A

H1 1A

Sc3 3B

Ti4 4B

V5 5B

Cr6 6B

Mn7 7B

Fe8

Co9

Rb

SrY

ZrN

bM

oTc

Ru

Cs

Ba

Hf

TaW

Re

Os

FrR

aR

fD

b

Sg

Bh

Hs

Mt

Pr Pa

Nd U

Pm Np

Sm PuRh

2

804830

794729

78 110

4628

814931

825032

835133

845234

855335

865436

1314

1516

1718

56

78

910

1920

1112

34

1

2122

2324

2526

27

3738

3940

4142

4344

5556

7273

7475

76

8788

104

105

106

107

108

109

45 77

4.00

3

26.9

8228

.086

30.9

7432

.066

35.4

5339

.948

22.9

9024

.305

10.8

1212

.011

14.0

0715

.999

18.9

9820

.180

6.94

19.

012

1.00

8

65.3

863

.546

58.6

9369

.723

72.6

474

.922

78.9

679

.904

83.7

9839

.098

40.0

7844

.956

47.8

6750

.942

51.9

9654

.938

55.8

4558

.933

(281

)(2

23)

(226

)(2

67)

(268

)(2

71)

(272

)(2

70)

(276

)

112.

412

107.

868

106.

4211

4.81

811

8.71

112

1.76

012

7.60

126.

904

131.

294

85.4

6887

.62

88.9

0691

.224

92.9

0695

.96

(98)

101.

0710

2.90

6

200.

5919

6.96

719

5.08

520

4.38

320

7.2

208.

980

(209

)(2

10)

(222

)13

2.90

513

7.32

817

8.49

180.

948

183.

8418

6.20

719

0.23

192.

217

2 3 4 5 6 71

Lant

hani

de S

erie

s

Act

inid

e S

erie

s

Ce Th

Ytt

erb

ium

No

be

lium

Th

uliu

m

Me

nd

ele

viu

m

Erb

ium

Fe

rmiu

m

Ho

lmiu

m

Ein

ste

iniu

m

Dys

pro

siu

m

Ca

lifo

rniu

m

Te

rbiu

m

Be

rke

lium

Ga

do

liniu

m

Cu

riu

m

Eu

rop

ium

Am

eri

ciu

m

Pra

seod

ymiu

m

Pro

tact

iniu

m

Ne

od

ymiu

m

Ura

niu

m

Pro

me

thiu

m

Ne

ptu

niu

m

Sa

ma

riu

m

Plu

ton

ium

Ce

riu

m

Th

ori

um

70 102

69 101

68 100

67 99

66 98

65 97

64 96

63 95

59 91

60 92

61 93

62 94

58 90

173.

055

(259

)

168.

934

(258

)

167.

259

(257

)

164.

930

(252

)

162.

500

(251

)

158.

925

(247

)

157.

25

(247

)

151.

964

(243

)

140.

908

231.

036

144.

242

238.

029

(145

)

(237

)

150.

36

(244

)

140.

116

232.

038

Ir

He

lium

Alu

min

um

Sili

con

Ph

osp

ho

rus

Su

lfu

rC

hlo

rin

eA

rgo

nS

od

ium

Ma

gn

esi

um

Bo

ron

Ca

rbo

nN

itro

ge

nO

xyg

en

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ori

ne

Ne

on

Lit

hiu

mB

ery

lliu

m

Hyd

rog

en

Zin

cC

op

pe

rN

icke

lG

alli

um

Ge

rma

niu

mA

rse

nic

Se

len

ium

Bro

min

eK

ryp

ton

Po

tass

ium

Ca

lciu

mS

can

diu

mT

ita

niu

mV

an

ad

ium

Ch

rom

ium

Ma

ng

an

ese

Iro

nC

ob

alt

Ca

dm

ium

Silv

er

Pa

llad

ium

Ind

ium

Tin

An

tim

on

yT

ellu

riu

mIo

din

eX

en

on

Ru

bid

ium

Str

on

tiu

mY

ttri

um

Zir

con

ium

Nio

biu

mM

oly

bd

en

um

Te

chn

eti

um

Ru

the

niu

mR

ho

diu

m

Me

rcu

ryG

old

Pla

tin

um

Th

alli

um

Le

ad

Bis

mu

thP

olo

niu

mA

sta

tin

eR

ad

on

Ce

siu

mB

ari

um

Ha

fniu

mT

an

talu

mT

un

gst

en

Rh

en

ium

Osm

ium

Irid

ium

Fra

nci

um

Ra

diu

mR

uth

erf

ord

ium

Du

bn

ium

Se

ab

org

ium

Bo

hri

um

Ha

ssiu

mM

eit

ne

riu

m

8B

Ds

Dar

mst

adtiu

mR

oent

geni

um

111

Rg

(280

)

La Ac

57 89 (227

)

138.

905

La

nth

an

um

Act

iniu

m

Lu Lr

Lu

teti

um

La

wre

nci

um

71 103

174.

967

(262

)



Choose the best answer for each question.

1 Which element is found in all of these compounds?

C2H6 NaHCO3 C6H12O6 CO2

A Oxygen

B Sodium

C Hydrogen

D Carbon

2 How many atoms of carbon are found in glucose, C6H12O6?

F 3

G 6

H 12

J 24

3 A molecule that contains two or more elements is called —

A an atom

B a mixture

C an ion

D a compound

Assessment—Analyzing Chemical Formulas


SAMPLE

64


Engage

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Which Does Not Belong?

In your science notebook, copy the list below. Circle the one word that does not belong in the group. Finish the statement that explains why it does not belong.

1. silver, nickel, cobalt, iron (not . . . )

2. neon, nitrogen, helium, argon (not . . . )

3. group, period, seven, horizontal rows (not . . . )

4. vertical column, group, period, valence electrons (not . . . )

5. sodium chloride, carbon dioxide, lead, lithium sulfide (not . . . )

6. Cu, Ag, H2O, Au (not . . . )

7. CH4, NaOH, C6H6, C6H12O6 (not . . . )

Explore

Matching Game

Working in small groups, match the graphic card model with a possible chemical formula.

SAMPLE



65


Explain, Part 1

Review the Explore card matching activity in a class discussion.

• What do the letters represent?

• What is the total number of shapes on each card?

Explain, Part 2

Analyzing Chemical Formulas

All compounds have definite compositions that can be represented by a chemical formula. Remember that chemical formulas use symbols or a combination of symbols and subscripts to show the elements and the number of atoms of each element that make up the molecule.

For example, the formula for oxygen gas is O2. The subscript indicates two oxygen atoms are bonded in an oxygen molecule as shown in Figure 2.32.

Figure 2.32. Oxygen Molecule

O O

Another common chemical formula is H2O. As shown in Figure 2.33, H2 represents 2 atoms of hydrogen and O represents 1 atom of oxygen. H2O is the chemical formula for the inorganic compound known as water.

Figure 2.33. Molecule of Water

H H

O SAMPLE

66


The inorganic compound magnesium hydroxide is written as Mg(OH)2. Notice the subscript after the parentheses in Figure 2.34. The subscript indicates there are 2 sets of the OH molecule.

Chemical formulas are a shorthand way to communicate the parts of a molecule. Subscripts are used in formulas to identify how many atoms of a particular element are present. In some cases, parentheses are used to indicate elements grouped together as a molecule within the compound.

Figure 2.34. Magnesium Hydroxide

Mg(OH)2

H HO OMg

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Atoms per Element

Identify the elements found in each of the following compounds. Then determine the number of atoms in each element.

1. carbon dioxide—CO2

2. glucose—C6H12O6

3. calcium hydroxide—Ca(OH)2

SAMPLE



67


Explain, Part 3

Using Coefficients and Subscripts

A coefficient indicates the number of molecules of a compound or element. For example, 6 molecules of water is written as 6H2O.

Figure 2.35. Parts of a Compound

6H2OCoefficient—There are 6 molecules of water.

Subscript—There are 2 atoms of hydrogen in each of the 6 molecules of water.

No subscript—There is only 1 atom of oxygen in each of the 6 molecules of water.

A visual can also be used to help determine the total number of atoms. The coefficient indicates there are 6 molecules of water.

Figure 2.36. Visual Model of a Compound

H H

OH H

O

H H

OH H

O

H H

OH H

O

Here’s another way to determine the number of atoms of each element:.

To determine the number of atoms in 6H2O:

6 molecules x 2 hydrogen atoms = 12 hydrogen atoms

6 molecules x 1 oxygen atom = 6 oxygen atoms

SAMPLE

68


Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Chemical Formulas

In your science notebook, write the chemical formula for each of the following. Place the proper coefficient in the blank and any subscripts needed in the appropriate boxes.

1. H

O

2. H

O

3. C

H

Cl

Copy the following formulas into your science notebook. Determine the number of atoms per element represented in each of the following substances. Justify your answers mathematically or with a drawing.

4. 3CO2

5. 2CaSO3

6. 2Ca(OH)2

H HO O

H H

O

H H

O

H H

O

C Cl

H

H

H C Cl

H

H

H

SAMPLE



69


Elaborate

Follow your teacher’s instructions to complete the Composition of Compounds handout.

Science


9 �/� x 7 �/� in. • 24.7 x 19.0 cm

Reflection

A friend is having difficulty writing chemical formulas. Create a list of guidelines to help your friend write chemical formulas.

Evaluate

Use the Periodic Table and your knowledge of compounds and chemical formulas to complete the assessment.

SAMPLE

Documents

SAMPLE - Region 4 Service Center STAAR Grade 8 Sample Lesson w… · group prior to class. Teacher Instruction ... SAMPLE. Matter and Energy. Advance Preparation • • • • •