Grade 8 Unit M .1 - Atoms and Molecules

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Atoms and Molecules

Grade 8 Unit M .1 - Atoms and Molecules

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Discussion….

What does the word Chemistry mean?

Where does the word Chemistry come from?

Who is the man on the front cover?

What does the diagram in Arabic tell you about Arabs and Science?

For the teacher, please visit: http://www.muslimheritage.com/topics/default.cfm?TaxonomyTypeID=18&TaxonomySubTypeID=77&TaxonomyThirdLevelID=221&ArticleID=1004 http://forum.khurram.ca/viewtopic.php?t=972

Grade 8 Unit M .1 - Atoms and Molecules

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Standards:

8.12.1 Know

that the smallest particle of an element is an atom and that atoms

of one element are of one kind and are different from atoms of

every other element

8.12.2 Know that elements join together chemically to form

compounds, that the smallest particle of a compound is a molecule,

and that all molecules of a compound are made up of the same

fixed number of atoms of the constituent elements.

8.12.3 Know that all elements can be represented by a symbol,

compounds by formulae and reactions by equations

8.12.4 Know that mass is conserved during a chemical reaction and

that the number of atoms of each element taking part in the

reaction remains unchanged

Objectives 1. Know that the smallest part of an element is an atom.

2. Know that elements join together chemically to form

compounds.

3. Define the molecule and understand that it is made of fixed

number of atoms.

4. Know how to represent the elements and compounds.

KEY WORDS

Atom انذرة

Symbol رمش

Element عىصز

Compound مزكب

Molecule جشيء

Formula صغت

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:وشبط

. قم بأحذ سهسهت مه انخزس، اقسم انسهست انى انىصف ثم انىصف انى ان تىته بحبه واحذة مه انخزس

Atoms انذراث

More than 2400 years ago, Greek philosophers suggested that

it is possible to divide a sample of matter into smaller and

smaller pieces but eventually, you would not be able to cut

anymore. You would have only one particle left. They

named theses particles atoms, a term that means "can

not be divided".

أ اى ا مغ أ لطؼخ ااد اخزفخ ا عخ ، ألزشح ف١غف ٠ب 2400لج أوضش

از انذرة لذ الزشح رغ١خ زا اجضء . اوضش لظدلطغ طغ١شح دز زط ا أطغش جضء ال ٠ى

.مه انى اجشاء اصغزيقسثانذي ال مكه ٠ؼ

Atoms Everything is made from atoms, including you. Atoms are tiny particles

that are too small to see, even with a microscope. ب ازساد جض٠ئبد زب١خ ف اظغش ال ٠ى سؤ٠ذ. رزى و االش١بء ازساد ثب ف١ب اجغبب

.وشعىة ثبعزذذا اثبؼ١ ال دذ

Figure 2

Exploring activity:

How to picture the atom:

Bring a string of beads like the one

shown if Figure 1. Divide the string

of the beads in half, and in half again

until you eventually come to one single

bead.

Figure 1: like this string of beads, all

matter can be divided until you reach

one basic particle, the atom.

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We usually imagine atoms as being like tiny balls, to make diagrams

simpler we often draw atoms as circles.

. زخ١ ػبدح شى ازساد ض وشاد طغ١شح، زجغ١ظ سعب شعب ػبدح ػ شى دائش

Elements انعىبصز

There are over a hundred different types of atom, and these are

called elements. Each element has a special name. For example

carbon, oxygen and hydrogen are all elements. ى ػظش اع خبص ث ، فضال اىشث، . االاع اخزفخ ازساد رغ اؼبطش بن ائبد

.ا١ذسج١ االوغج١ رؼذ وب اؼبطش

Lead and gold are elements too. A piece of pure gold contains only

gold atoms. A piece of pure lead contains only lead atoms.

وب . فمطؼخ ازت اخبض رزى فمظ رساد ػظش ازت. ص ازت وزه اؼبطشاشطب

.رزى لطؼخ اشطبص رساد ػظش اشطبص فمظ

Some substance cannot be broken down into anything simpler. This

is because all the atoms inside them have the same type.

These substances are called elements. ثؼض ااد ال ٠ى رمغ١ب اوضش ا جض٠ئبد اطغش ره ال ج١غ ازساد ف ز ابد فظ

.اع

Atom: is the smallest particle of an element that cannot be split. .رفخ از ال ٠ى رمغ١ اوضشاطغش جضئ ف اؼبطش اخ: انذرة

Figure 3

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Look at the examples of elements:

اىس غبص 5شكم ف, اذذ٠ذ ػض طت ٠زى فمظ رساد ػظش اذذ٠ذ 4انشكم ف

.٠زى فمظ رساد ػظش اىس

Symbols انزمىس

Each element is given its own chemical symbol,

like O for oxygen and Cl for chlorine. .ى ع ازساد اع سض و١١بئ

Chemical symbols are usually one or two letters

long, but sometimes three letters are used. For

example, Uut is Ununtrium. دشف ا دشف١ ى ف ثؼض االلبد ٠زى ٠زى اشض اى١١بئ

.ادشف 3

Every chemical symbol starts with a capital

letter, with the second or third letters written

in lower case. سض و١١بئ ثذشف وج١ش ث١ب ٠ى اذشف اضب اضبش ثأدشف ٠جذأ و

.طغ١شح

Figure 6

Figure 4

Figure 5

Elements: Molecules that are made up of the same type of atoms . جض٠ئبد رزى فظ اع ازساد: انعىبصز

Figure 4

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For example, Mg is the correct symbol for magnesium, but mg, mG and

MG are wrong.

Take care to write chemical symbols correctly

Most symbols resemble their English name. Some are based on their

original Latin names. ثؼض اشص رض . دشف أ األدشف األ االع االج١ض ؼظش اي٠ض اشض ف اؼظ

.ؼظش طاالع االر١ األ Look at the table in Figure 6

Which atoms have symbols based on Latin names? اؼبطش ف اجذي رؼزذ سصب ػ االع االر١؟ أ

Why is the symbol for helium He and not H?

Notice that you always use capital letter for the first letter of symbol.

If the symbol has a second letter, it is always a small letter. Refer to

examples in Figure 6. غزخذ األدشف اىج١شح، إرا وب اشض ٠زى دشف١ ٠ىزت األي ثذشف وج١ش اؼظش ػذ وزبثخ سض

.اضب ثذشف طغ١ش

Molecules ث انجشئب

Atoms are nature's building blocks. A molecule is formed when

two or more atoms join together chemically.

.ػذب رشرجظ رسر١ أ اوضش ثشاثظ و١١ب٠ئخ رزى اجض٠ئبد. ازساد دذح اجبء االعبع١خ

Molecular hydrogen (H2), molecular oxygen (O2) and molecular

nitrogen (N2) are not compounds because each is composed of a

single element.

جض٠ئ ا١ذسج١، االوغج١ أ ا١زشج١ ال رؼزجش شوجبد الب رزى ع ادذ

.اؼبطش اى١١بئ١خ

Water (H2O), carbon dioxide (CO2) and methane (CH4) are

compounds because each is made from more than one element.

Grade 8 Unit M .1 - Atoms and Molecules

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ا١ضب شوجبد رزى رساد ؼبطش و١١بئ١خ خزفخ ابء غبص صب اوغ١ذ اىشث أ

.شرجطخ غ ثؼضب اجؼض

The smallest bit of each of these substances would be referred

to as a molecule. For example, a single molecule of molecular

hydrogen is made from two atoms of hydrogen while a single

molecule of water is made from two atoms of hydrogen and one

atom of oxygen.

.ػذب رشرجظ ازساد غ ثؼضب اجؼض ثشاثظ و١١بئ١خ رزى اجض٠ئبد

.و١١بئ١خ غ ثؼضب اجؼض رسر١ أ أوضش شرجطخ اجض٠ئبد جػخ

Oxygen molecule

Compounds انمزكببث

There are only 92 elements in nature and

therefore 92 different types of atoms.

However, there are millions of different

substances.

ع ازساد 92ع اؼبطش ف اطج١ؼخ رزى 92بن فمظ

.ى بن اال١٠ ااد اخزفخ.

Molecules are groups of 2 or more atoms

chemically bond together.

Figure7

Molecule of Ammonia

H N

H

H

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Most matter or substances is made of more than one element.

Substances that is made of more than one element is called a

compound. Some examples of compounds are water (H20),

table salt NaCl), table sugar C6H1206), and chalk (CaCO3).

وجبد االضخ ش .ػ١ أ أوضش ازساد اشرجطخ ؼب ثشاثظ و١١بئ١خ رذز اشوجبد ػ

.جض٠ئ ابء جض٠ئ خ اطؼب جض٠ئ اغىش وزه افذ

Note that even in the figure 6, Methane, which is very small, is called both

a molecule and a compound.

.،غبص ا١ضب جض٠ئ شوت ف فظ الذ 6اشى ف اضبي ف

A compound is two or more different atoms bonded. A molecule is two or

more of the same atoms or different elements bonded. ٠زج اجض٠ئ اسرجبط رسر١ ا ث١ب. ٠زج اشوت اسرجبط رسر١ ا اوضش ااع خزفخثشاثظ و١١بئ١خ

.اوضش فظ اع ا ااع خزفخ ثشاثظ و١١بئ١خ

A molecular compound is a small number of different atoms

that are commonly bonded.

Chemical Formula اظ١غخ اى١١بئ١خ

Chemists used a kind of shorthand to describe molecules.

It is called the chemical formula. . اظ١غخ اى١١بئ١خ رؼج١ش ػ اشوجبد ٠ؼشف ثبع وزبثخخزظش اي ٠غزخذ اؼبء شى

Formulas tell you which atoms are in the molecule by looking at the

symbols. .أاع ازساد رى اجض٠ئبد أرذب ػ حاظ١غخ اى١١بئ

A compound is a substance formed when two or more elements are

chemically joined. .عىذ ارتببط عىصزه أو أكثز بزوابظ كمبئتانمزكببث ه مىاد تتكىن

Grade 8 Unit M .1 - Atoms and Molecules

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It also tells you how many atoms there are by small numbers after

each symbol. The smaller number is called the subscript. For Example:

CO2 means 1 Carbon atom and 2 Oxygen atoms.

Notice that, if there is just one atom it is not numbered. غ الدظخ ا إرا وب . وب رذب و ػذد ازساد و ع ثبعزخذا سل طغ١ش ٠ىزت ثؼذ و ػظش

فضال ف صب اوغ١ذ اىشث ٠زى رسر١ .سل أعف اؼظش أبن رسح ادذح اؼظش ال ىزت

. االوغج١ رسح وشث

Example: H2O is the chemical formula for _____________. It has

____Hydrogen atom(s) and ______ _ oxygen atom (s).

Table 1 shows some common molecules .٠ج١ اجذي ثؼض اجض٠ئبد اشبئؼخ

Table 1

Other examples are shown in Table 2.

Compound Molecular element

Water H2O Hydrogen H2

Carbon dioxide CO2 Oxygen O2

Glucose C6H12O6 Ozone O3

Sodium chloride NaCl Chlorine Cl2

Magnesium sulfate MgSO4 Sulfur S8

Table 2: List of some common

molecules represented by their

chemical formulas.

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1 Look at the three diagrams. ادرس الشكل السابق جدا ثم اجب عن االسئلة التالة

a i One diagram represents solid iron. Which one?

احد االشكال يمثل عنصر الحديد الصلب

ii Explain why you chose your answer.

سر سبب اختيارك لهذه االجابةف

iii Why is this substance an element?

لماذا تمثل هذه المادة عنصر كيميائي؟

2 Copy the table and write the substances into the correct column.

اكتب اسم كل مادة أسفل العمود المناسب

Element Molecule

A C B

carbon copper

NaCl

water

carbon dioxide

gold helium

methane

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3 - Define the following: (CS 8.12.1,8.12.2)

:المصطلحات العلمة التالة عرف

Atom:

_____________________________________________________________

_____________________________________________________________

Element:

_____________________________________________________________

_____________________________________________________________

4 -Write the symbols of these elements:

اكتب الرمز الكيميائي للعناصر التالية

Symbol Atom

Hydrogen Helium Nitrogen Neon Oxygen Carbon Chlorine Calcium Copper Magnesium Aluminum

Sulphur Iron

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5- Choose the correct answer: اختز االجببت انصححت

a) Which is the symbol for carbon?

اشض اى١١بئ ىشثأ ب ٠ ٠ض

a) Co b) C c) Ca d) Cr

b) Which of these is an element?

أ ب ٠ ٠ض ػظش و١١بئ

a) Magnesium b) Water c) Carbon dioxide d) Zinc oxide

c) Which is the chemical symbol for the element zinc?

أ ب ٠ اشض اى١١بئ ؼظش اخبسط١

a) ZnO b) Zn c) ZrC d) ZnS

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6- Complete the sentences, using words from the list below.

:أكمل الجمل باستخدام الكلمات في القائمة

1. When 2 or more __________ bond together, we get a

_____________.

2. If a substance is made up of 2 or more different types of

___________, it is called a ___________________.

3. An ________ is a substance made up of only one type of

_________, they can’t be __________ down into ________

substances.

7- The diagrams below show the particles in some substances.

تمثل الرسوم التوضحة التالة اشكال الجزئات ف بعض المواد

a Which substances are compounds?

مركبات؟أي المواد تمثل

b Which substances are elements?

أي المواد تمثل عناصر ؟

c Explain below how you could tell the difference.

فسر سبب هذه االجابات

Atom broken simpler element Molecule atom compound atoms

A B C E D

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8- Complete the following table:

Formula Write down the

symbols of each

atom in the

molecule

Write down the

number of each

kind of atom in

the molecule

Write down

the name of

each element

in the molecule

1 H2O

2 CH4

3 Na2SO4

4

NH4OH

5

Mg3(PO4)2

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H.W.

The chemical formula of carbon dioxide is CO2.

CO2الصغة الكمائة لثان اكسد الكربون ه

a. Explain why carbon dioxide is a compound and not an element. فسر لماذا عتبر ثان اكسد الكربون مركب و لس عنصر

______________________________________

b. How many carbon atoms are there in one molecule of carbon

dioxide? كم عدد ذرات الكربون ف جزئ واحد من ثان اكسد الكربون

_________

9- Complete the table below by writing the chemical formula for the

compound. The first one is done for you. المثال االولالجدول التال بكتابة الصغة الكمائة المناسبة كما ف أكمل

Molecule

Question Chemical

formula

Sodium chloride is a compound which has 1

Sodium atom and 1chlorine atom

NaCl

Calcium fluoride,1 Calcium, 2 Fluorine

Nitrogen dioxide, 1 nitrogen, 2 oxygen

Methane, 1 carbon, 4 hydrogen

Ammonia 1 nitrogen, 3 hydrogen

Grade 8 Unit M .1 - Atoms and Molecules

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Standard:

8.12.4 Know that mass is conserved during a chemical reaction and that

the number of atoms of each element taking part in the reaction

remains unchanged

Objectives:

Know that the mass is conserved during a chemical reaction.

Key Words

Chemical Reaction تفبعم كمبئ

Equation, معبدنت

Reactant متفبعالث

Product وىاتج

Balance. متىاسن

Mass كتهت

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Chemical reactions Chemical changes produce new substances

that have properties different from those of the original substances.

The rust on a bike's handlebars, for example, has properties different

from those of the metal around it. A process that produces chemical

change is a chemical reaction. ضال طذا اذذ٠ذ .جذ٠ذح راد طفبد خزفخ ػ ابدح االط١خ از زجذ بازغ١شاد اى١١بئ١خ رزج اد

.رزج ازغ١شاد اى١١بئ١خ ز١جخ ػ ازفبػالد اى١١بئ١خ.٠خزف ف اشى ػ اذذ٠ذ اذ١ظ ث

Exploring activity:

Observing a chemical reaction:

Bring a piece of paper and matches as

shown in Figure 1. Use the match to set

fire to the paper. Caution: Be careful when

using matches. Look for the changes will

happen to the paper after the burning

process. ازغ١شاد از طف. د اىجش٠ذرخذا ػل ثبشؼبي سلخ ثبط

.طشأد ػ اسلخ ثؼذ دشلب

Figure 1: burning the paper creates new

substance, there for burning is a chemical

change.

Chemical reaction: Process in which new substances with new

chemical and physical properties are formed. .ح راد طفبد ف١ض٠بئ١خ و١١بئ١خ خزفخ ػ١خ ٠زج ب بدح جذ٠ذازفبػ اى١١بئ

Grade 8 Unit M .1 - Atoms and Molecules

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In any chemical reactions, the substance or substances initially

involved in a chemical reaction are called reactants. Chemical reactions

are characterized by a chemical change, and they yield one or more

products which are, in general, different from the reactants.

رز١ض ازفبػالد اى١١بئ١خ . ااد اغزخذخ ف ثذا٠خ ازفبػ ثبزفبػالدف أ رفبػ و١١بئ ، رغ

.ثزغ١شاد و١١بئ١خ از رزج برج ا اوضش ٠خزف ػ ازفبػالد

Reactant: substances that is changed in a chemical reaction. . ااد از ٠طشأ ػ١ب رغ١شاد ف ازفبػالد اى١١بئ١خ :انمتفبعالث

Lesson 2

Product: substances that is formed in a chemical reaction. . ااد از رزى ز١جخ زفبػالد اى١١بئ١خ: انىىاتج

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Chemical equations: : انكمبئت ةانمعبدل

Are bubbles are the only product out of

the reaction, or do some atoms from the

vinegar and baking soda form something

else? What goes on in the chemical

reaction can be more than what you see

with your eyes.

ب ٠ذذس ف افمبػبد ابرج اد١ذ ازفبػ أ ا

.ازفبغالد اى١١بئ١خ أوضش أ ٠الدظ ثبؼ١ فمظ

Chemists try to find out which reactants are used and which products

are formed in a chemical reaction. Then, they can write it in a

shorthand form called chemical equation. ٠ذبي اى١بئ١ ؼشفخ أ ازفبػالد اعزه أ اارج رى ف ازفبػالد اى١١بئ١خ، ص ٠ضا

.ببنمعبدنت انكمبئت خزظشح رؼشفازفبػ ثطش٠مخ

Mini Lab:

Describing a chemical reaction:

Procedure:

Place about 1g of baking soda in an

evaporating dish. Add 2ml of white vinegar.

1- Allow the mixture to dry

2- Examine the result and compare it with

baking soda. Do they look the same?

Analysis:

1- What do the bubbles formed in

Figure 2 tell you?

Figure 2: Bubbles are formed when

baking soda is added to the vinegar.

(:وصف انتفبعم انكمبئ) مختبز

:انطزقت

ج ث١ىشثبد اظدا ف 1ضغ رمش٠جب

اخ 2أضف . طجك ازجخ١ش

.ارشن اخ١ظ ١جف. االث١ض

اوشف ػ ابرج لبس ثجىشثبد

.اظدا

ابدر١ زشبثز١؟

ػ برا رذه افمبػبد ابرجخ؟

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One way you can describe a chemical reaction is with an equation that

uses words to name the reactants and products.

ح ؼبدخ ثبعزخذا األعبء ف ازؼج١ش ػ أدذ اطشق اغزخذخ طف ازفبػ اى١١بئ وزبثت

:ازفبػالد اارج وب ف اضبي ازب

Baking soda + Vinegar Gas + white solid (Word equation) (انمعبدنت انكالمت) مبدة بضبء صهبت + غبس انخم_+بكزبىوبث انصىدا

Sometimes, the word equation for the reaction can be long. That's

why chemist use chemical formulas to represent the chemical names of

substances in the equation

اى١١بئ١خ ػذب رى اؼبدخ اىال١خ ط٠خ، ٠غزخذ اى١١بئ١ اظ١غ اى١١بئ١خ زؼج١ش ػ االعبء

:اد ف اؼبدخ وب ف اضبي

HC2H3O2 + NaHCO3 CO2 + NaC2H3O2 (Formula

equation)

The reaction between Iron and Sulphur can be shown by a word

equation( figure 3) اى رض١ ازفبػالد اى١١بئ١خ ثؼبدخ وال١خ

Reactants Product

Iron + sulphur iron sulphide

Chemical equation: statements in which chemical formulas are used to

describe a chemical reaction. . اؼجبسح از رغزخذ ف١ب اظ١غ اى١١بئ١خ طف ازفبػ اى١١بئ: انكمبئت انمعبدنت

Figure3 showing the reaction

of Iron and Sulphur

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The substances that we start with are called reactants. .رؼشف ااد از جذأ ثب ف ثذا٠خ ازفبػ ثبزفبػالد

The substances made in reactions are called products.

رؼشف ااد از رزى ازفبػ اى١١بئ ثبارجIn the above example Iron and Sulphur are reactants and Iron sulphide is the product. Fe +S FeS

This tells us that 1 atom of iron reacts with 1 atom of sulphur. They

make iron sulphide,

This contains one iron atom for each sulphur atom.

The atoms have been chemically bonded together.

The new compound, iron sulphide, is not like iron or sulphur at all. .اسرجطذ ازساد ؼب ثشاثظ و١١بئ١خ، جذ أ ابدح ابرجخ رخزف ػ ازفبػالد

It has totally different properties. A new substance has been made. .اارج ب طفبد خزفخ و١ب ػ ازفبػالد رض بدح جذ٠ذح و١ب

Conservation of Mass قبوىن بقبء انكتهت

What happens to the atoms in the reactants when they are converted

into products? Do they disappear? د أخزفذ؟برا ٠ذذس زساد ازفبػالد ػذب رزذي ا اارج؟ رؼزمذ اب ق

No. According to the law of conservation of mass, the mass of a closed

system of substances will remain constant, regardless of the processes

acting inside the system. An equivalent statement is that matter

changes form, but cannot be created nor destroyed. This implies that

for any chemical process in a closed system, the mass of the reactants

must equal the mass of the products. طجمب مب ثمبء اىزخ ، ف أ رفبػ و١١بئ ٠ز داخ ظب غك، ثغض اظش ػ طج١ؼخ ازفبػ فب

.ب ى ال ٠ى أ رف أ رغزذذس ػذوزخ ااد رجم صبثزخ أ أ ابدح رغ١ش شه

.ثبءا ػ ره فب وزخ ازفبػالد الثذ أ رى غب٠خ ىزخ اارج

Law of conservation of mass: A relation stating that in a

chemical reaction, the mass of the products equals the mass of

the reactants. :قبوىن بقبء انكتهت

.رضخ ا ف أ رفبػ و١١بئ، وزخ اارج غب٠خ ىزخ ازفبػالد ػاللخ

Grade 8 Unit M .1 - Atoms and Molecules

23

Standard:

8.12.4 Know that mass is conserved during a chemical

reaction and that the number of atoms of each

element taking part in the reaction remains unchanged

Objectives:

*Know that the number of atoms of each element taking part

in the reaction is unchanged

Balancing chemical equations:

Balancing Chemical Equations is absolutely essential if you want to

determine quantities of reactants or products. A balanced equation

assures that the Conservation Law of matter is obeyed. The total mass

of reactants must equal the total mass of products. A balanced

equation is like a recipe. It tells you the proportional quantities of

each substance involved, Figure 4.

رغبػذب وزه ف رذذ٠ذ مذاس , ص اؼبدخ اى١١بئ١خ طش٠مخ ضب رذم١ك لب ثمبء اىزخ

. ازفبػالد اارج

Figure 4: Every atom

that appears on the

reactant side of the

equation also e

appears on the

product side.

Balanced equation: the number of

atoms of each element is equal on both

sides of the equation. :انمعبدنت انكمبئت انمىسووت

ؼبدخ ٠زغب ف١ب ػذد رساد و ػظش ػ جبج

.اؼبدخ

Grade 8 Unit M .1 - Atoms and Molecules

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Balancing chemical equation

Rules for Balancing Equations:

Five steps to write a balanced equation

:خطاد ص أ ؼبدخ و١١بئ١خ 5بن

1. Write the word equation for the reaction

.أوزت اؼبذح اىال١خ زفبػ -1

2. Write the symbols and formulas for reactants and products.

. اظ١غ اى١١بئ١خ زفبػالد اارجأوزت اشص -2

3. Count the number of atoms of each element on each side of the arrow.

.ل ثؼذ ػذد رساد و ػظش ػ جبج اغ از ٠فظ ث١ طشف اؼبدخ -3

4. Balance the equation using coefficients. Put a coefficient in front of a symbol of

formula, so that the same number of each type of atoms appears on both

reactant side.

.ثذ١ش ٠زغب اطشف١ص اؼبدخ ثىزبثخ اشل ابعت أب و سض -4

5. Check to see that the coefficients used are the smallest whole numbers that

give the balanced equation.

.لبس طشف اؼبدخ -5

Below is an example of how you can balance an equation

When hydrogen and oxygen react, the product is water. Write a

balanced equation for this reaction.

ابءاضبي ٠ض رفبػ ا١ذسج١ غ االوغج١ زى٠

Solution:

Grade 8 Unit M .1 - Atoms and Molecules

25

Since the chemical formulas of the reactants and products are known,

we can write a skeleton equation.

H2(g) + O2(2g) H2O(l)

Hydrogen is balanced but oxygen is not. If we put a coefficient of 2 in

front of H2O, the oxygen becomes balanced.

H2(g) + O2(g) 2H2O(l)

Now there is twice as many hydrogen atoms in the product as there are

in the reactants. To correct this, put a coefficient of 2 in front of H2.

The equation is now balanced.

2H2(g) + O2(g) 2H2O(l)

Check the coefficients. They must be in their lowest possible ratio

2(H2)s 1(O2), and 2(H2O).

Here we notice the mass of the reactants also remains constant.

# of atoms in reactants = # of atoms in products ازساد ف اارجػذد = ػذد رساد ازفبػالد

Grade 8 Unit M .1 - Atoms and Molecules

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Key Questions:

1- How do we represent chemical equations? Provide an example.

.ذلككف مكننا تمثل المعادلة الكملئة؟ أعط مثال على

2- Write the word equation for each one of the following reactions:

:أكتب المعادلة الكالمية لكل من التفاعالت التالية

1. When magnesium reacts with oxygen it forms magnesium oxide.

2. When zinc reacts with oxygen it forms zinc oxide

3. Sodium reacts with hydrochloric acid ( HCl) and forms sodium

chloride and hydrogen gas.

4. When copper is heated in oxygen it forms a black solid called

copper oxide.

a Write down the name of the element that the copper reacted

with.

b Copy and complete this word equation:

Copper + +

Grade 8 Unit M .1 - Atoms and Molecules

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c Copy the table below and write the names of the substances

in your word equation into the table.

Element Compound

4. Kerry is burning some elements in oxygen.

a Kerry burns carbon in oxygen. It makes carbon dioxide. Some

of these are reactants. Some are products.

Copy and complete the sentences:

I Carbon is a:

.

ii Oxygen is a:

.

Iii Carbon dioxide is the

.

Iv Write the word equation

for this reaction.

Grade 8 Unit M .1 - Atoms and Molecules

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Key Questions:

1-What happens to the mass and the number of atoms in a chemical

reaction?

ماذا حدث لكتلة و عدد ذرات العناصر ف التفاعالت الكمائة؟

...............................................................................................................

2- Balance the following equations: لمعادالت التاليةزن ا

The first one is done for you.

1. 2 Mg + O2 2 MgO

2. C + O2 CO2

3. Na + MgF2 NaF + Mg

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4. Mg + HCl MgCl2 + H2

5. Cl2 + KI KCl + I2

6. NaCl Na + Cl2

7. Na + O2 Na2O

8. Na + HCl H2 + NaCl

9. K + Cl2 KCl

Grade 8 Unit M .1 - Atoms and Molecules

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References: شاجغ

1. http://chemistry.about.com/cs/stoichiometry/a/aa042903a.htm

http://education.jlab.org/qa/compound.html

http://www.lisisoft.com/imglisi/6/Science/3302methane.gif

http://www.sky-web.net/science/balancing_chemical_equations.htm

(http://www.chem4kids.com/files/react_intro.html

http://ssischem.wikispaces.com/file/view/511natgascombust.jpg/3007

2708/511natgascombust.jpg )

http://www.docbrown.info/ks3chemistry/8Enotes.htm

Rules for balancing equationTaken from: Chemistry

Wilberham, Staley, Simpson, Matta

Addison Wesley