8th Grade Science

Directed Reading Packet

Chemistry

Name: ___________________________

Teacher: _____________ Period: _____

What are Atoms?

1) Atoms are the building blocks of _______________. 2) _______________ are the smallest particles of an element.3) _______________ are pure substances.4) List 5 elements using your periodic table:

Size of Atoms

5) Atoms are extremely _______________. 6) _______________ atoms can fit inside the period at the end of this sentence.7) Which element on the periodic table do you think has the smallest atoms? _______________

Subatomic Particles

8) Fill in the chart below:

Subatomic Particle Electrical Charge Location in Atomproton in nucleus

electron negative

neutron

9) Draw a simple sketch of a Helium atom.

Summary

Atoms are the building blocks of _______________. They are the smallest _______________ of an

_______________ that still have the element’s _______________. All atoms are very

_______________, but atoms of different _______________ vary in size. Three main types of particles

that make up all atoms are_______________, _______________, and _______________.

Section 2: Atomic Nucleus

Section 1: Atoms

At the Heart of It All

1) The nucleus is a _______________ charged region at the center of the atom.2) The nucleus is made of two types of subatomic particles, _____________ and ___________.3) Draw a sketch of the nucleus of an Oxygen atom, which consists of 8 protons and 8 neutrons:

Size and Mass of the Nucleus

4) How does the size of the nucleus of an atom compare to the overall size of the atom?

5) How does the mass of the nucleus contribute to the overall mass of the atom?

Holding It All Together

6) Particles with opposite electric charges _______________ each other.7) _______________ charged electrons orbit the _____________ charged nucleus of an atom.

8) Draw a sketch of a carbon atom. It contains 6 protons, 6 neutrons and 6 electrons. Make akey to differentiate between the different types of subatomic particles.

Summary

The nucleus is a _______________, _______________ region at the center of an atom. It consists of positive _______________ and neutral _______________, so it has an overall _______________ charge.

The nucleus is just a tiny part of the atom, but it contains virtually all of the atom’s ___________.

Section 3: Energy Level

What are Energy Levels?

1) Energy levels are also called electron _______________. 2) Electrons have a_______________charge and orbit the atom’s _______________.3) What can be said about the energy of electrons as you move farther from the nucleus?

4) What happens when electrons jump from one energy level to another?

5) Draw an arrow pointing to the electron in the atom below with the most energy.

Energy Levels and Orbitals

6) Write the maximum number of electrons that can occupy the first 3 energy levels.

1st energy level _____ 2nd energy level _____ 3rd energy level _____

7) Electrons are always added to the _______________ energy level first.

The Outermost Level

8) What are valence electrons?

9) Why is helium considered a stable element (doesn’t react with other atoms)?

Summary

Energy levels are fixed distances from the _______________ of an atom where the _______________ may be found. As you go farther from the _______________, electrons at _______________ energy levels have _______________ energy.

Electrons are always added to the _______________ energy level first until it has the maximum number of electrons possible, and then _______________ are added to the next _______________ energy level until that level is full, and so on.

Electrons in the _______________ energy level of an atom are called _______________ electrons. They determine many properties of an atom, including how _______________ it is.

Section 4: Ionic Bonding

How Ionic Bonds Form1) What 2 types of ions are needed for ionic bonds to form?

2) Ions form when an atom _______________ or _______________ electrons.

3) What happens when a positive ion is near a negative ion?

4) Do you think the atom below will form a positive or negative ion? Explain your answer.

Why Ionic Bonds Form5) Ionic bonds form between _______________ and _______________.

6) List 5 elements on the periodic table that are metals:

7) List 5 elements on the periodic table that are nonmetals:

8) During ionic bonding, metals ___________ electrons and nonmetals ___________ electrons.

9) The goal in ionic bonding is for all atoms to have a __________ outer energy level of electrons.

10) Sodium (11) bonds with Chlorine (17). Predict another pair of elements that form an ionic bond.

Energy and Ionic Bonds11) It takes energy to move _______________ during ionic bonding. The more electrons that

move, the _______________ energy is gained or lost.

Summary An _______________ bond is the force of _______________ that holds together

_______________ and _______________ ions. It forms when atoms of a _______________ element give up electrons to atoms of a _______________ element.

Ionic bonds form only between _______________ and _______________. That because metals “want” to _______________ electrons, and nonmetals “want” to _______________ electrons.

It takes _______________ to remove valence _______________ from an atom and form a_______________ ion. Energy is _______________ when an atom gains _______________ electrons and forms a _______________ ion.

Section 5: Covalent Bonding

Sharing Electrons

1) A ___________ is the force of attraction that holds together atoms that share ____________.

2) The shared electrons are attracted to the nuclei of _______________ atoms in the bond.

3) Covalent bonds form only between atoms of _______________.

Covalent Compounds and Diatomic Elements4) Water is an example of a simple covalently bonded molecule. Fill in the electrons on the

sketch of a water molecule. Show how the electrons are shared.

5) How many valence electrons does the oxygen atom share with each hydrogen atom?

6) How many covalent bonds hold the water molecule together?

7) Try to draw a sketch showing the electrons of a covalent bonded molecule of HCl.

Why Covalent Bonds Form8) Covalent bonds form because they give atoms a more ______________ arrangement of electrons.

9) When covalent bonding is complete, all atoms have a _____________ outermost energy level of electrons.

Summary A _______________ bond is the force of _______________ that holds together atoms that

share a pair of _______________ electrons. Covalent bonds form only between atoms of _______________.

The two atoms that are held together in a covalent bond may be atoms of the _______________ element or _______________ elements. When atoms of ______________elements bond together, it forms a covalent _______________.

Covalent bonds form because _______________ electrons fill each atom’s _______________ energy level and this is the most _______________ arrangement of electrons.

HO

H

Section 6: Recognizing Chemical Reactions

What’s Your Sign?1) List 4 common signs that a chemical reaction has occurred:

1.

2.

3.

4.

Examples of Chemical Reactions2) Below each diagram, list the signs that a chemical reaction is occurring. The description for

each picture can be found in the Flexbook.

3) Mix a small amount of baking soda with some vinegar. This is a simple chemical reaction. What signs of a chemical reaction are present in this example?

4) Can you think of any other chemical reactions that commonly occur around you?

5) Is water freezing a chemical reaction? Why or why not?

6) The leaves change this time of year. Is that a chemical reaction? Why or why not?

1) Explain how a candle burning is a chemical change in matter:

Section 7: Reactants and Products

From Reactants to Products

2) What are reactants?

3) What are products?

4) List the reactants and products of the chemical reaction of a burning candle?

Reactants: Products:

Relating Reactants and Products

5) Circle the reactants in the following chemical reaction:

HCl + Na → NaCl + H2

6) Circle the products in the following chemical reaction:

CH4 + O2 → CO2 + H2O

7) What happens to the bonds between atoms in the reactants that allows them to form products?

Breaking and Making Chemical Bonds

8) Draw lines connecting the term on the left to the part of the chemical reaction on the right.

reactants

products

represents the breaking of bonds

Summary

All chemical _______________ involve both _______________ and _______________. Reactants are substances that _______________ a chemical reaction, and products are substances that are _______________ in the reaction.

A chemical reaction can be expressed by the general chemical formula:_______________ _______________

Bonds _______________ and _______________ during chemical reactions. _______________ and _______________ contain the same atoms, but they are _______________ during the reaction, so reactants and products are different _______________.

Chemical Reactions and Balanced Equations

Section 8: Conservation of Mass in Chemical Reactions

1) Chemical reactions are represented by chemical _______________.

2) Write the equation that represents methane combining with oxygen to form carbon dioxide and water.

Following the Law

3) Why must chemical equations be balanced?

4) What is the Law of Conservation of Mass?

Lavoisier and Conservation of Mass

5) In what century did Antoine Lavoisier live?

6) In what country did Antoine Lavoisier live?

7) Explain how Antoine Lavoisier concluded that the mass of the reactions must equal the mass of the products in a chemical reaction.

8) What element did Antoine Lavoisier discover? _______________

9) Draw a sketch of the instrument that Antoine Lavoisier used conclude that the mass of the reactants equals the mass of the products during a chemical reaction.

Summary

A chemical reaction occurs when some substances change _______________ to other substances. Chemical reactions are represented by chemical _______________.

All chemical equations must be _______________ because _______________ cannot be _______________ or _______________ in chemical reactions.

Antoine Lavoisier did careful _______________ to discover the law of conservation of _______________ in chemical reactions.

1) How is a chemical equation a little bit like a seesaw?

Section 9: Balancing Chemical Equations

Writing Chemical Equations

2) A chemical equation represents changes that occur during a chemical _______________.

3) Fill in the blanks to show the general form of a chemical equation:_______________ _______________

4) Look at the following equation: H2 + O2 H2O

What is wrong with the way the chemical equation is written?

Using Coefficients

5) Coefficients are used to balance chemical _______________. Coefficients are used to show how many _______________ or _______________ of a substance are involved in the reaction.

6) Circle the coefficients in the following chemical reactions:

CH4 + 2 O2 → CO2 + 2 H2O 2 H + CO3 → H2O + CO2 CaCl + 2 AgNO → Ca(NO3)2 + 2AgCl

Steps in Balancing a Chemical Equation

7) Try to balance the following chemical equations by adding coefficients in the spaced provided:

___H2 + ___O2 ___H2O ___N2 + ___H2 ___NH3

___Zn + ___HCl ___ZnCl2 + ___H2

Summary

A chemical _______________ represents the _______________ that occur during a chemical _______________. It has the general form: _______________ _______________. All chemical equations must be _______________. This means that there must be the _______________ number of atoms or molecules of the substance involved in the _______________.

_______________ are used to balance chemical equations. A coefficient is a _______________ placed in _______________ of a chemical symbol or formula. It shows how many _______________ or _______________ of the substance are involved in the _______________.

To balance a chemical equation, place _______________ as needed in front of the symbols or formulas so the _______________ number of each type of _______________ occurs in both _______________ and _______________.

Energy and Chemical Reactions

Section 10: Conservation of Energy in Chemical Reactions

1) During a chemical reaction, _______________ is used to break bonds in reactants, and _______________ is released when new bonds form in products.

2) How are exothermic chemical reactions different than endothermic chemical reactions?

Conservation of Energy3) What is the Law of Conservation of Energy?

4) Fill in the missing boxes with the correct terms to show your understanding of endothermic and exothermic chemical reactions.

5) Try to think of some examples of exothermic chemical reactions and list them below. Remember, exothermic reactions release energy.

6) Try to think of some examples of endothermic chemical reactions and list them below. Remember, endothermic reactions absorb energy.

Summary

All chemical reactions involve _______________. Energy is used to break bonds in _______________, and energy is released when new bonds form in _______________. _______________ reactions absorb energy, and _______________ reactions release energy.

The law of conservation of _______________ states that energy cannot be _______________ or _______________. Whether a chemical reaction _______________ or _______________ energy, there is no overall _______________ in the amount of energy during the reaction.

How Fast Does It Go?1) How fast a chemical reaction occurs is called the reaction _______________.

Section 11: Chemical Reaction Rate

2) List the factors that affect the rate of a chemical reaction:

Temperature of Reactants3) When the temperature of the reactants is higher, the rate of the reaction is _______________.

4) Why do reactions happen faster at higher temperatures?

5) Give an example of how temperatures can affect the rate of a chemical reaction.

Concentration of Reactants6) When the concentration of reactants is higher, the rate of the reaction is _______________.

7) Why do reactions happen faster with higher concentrations of reactants?

8) Give an example of how concentration of reactants can affect the rate of a chemical reaction.

Surface Area of Reactants9) Increasing the surface area of reactants _______________ the reaction rate.

10) Why do reactions happen faster when reactants have a greater surface area?

11) Give an example of how surface area of reactants can affect the rate of a chemical reaction.

Presence of a Catalyst12) A catalyst is a substance that _______________ the rate of a chemical reaction.

13) A catalyst isn’t ______________ or used up in a reaction.

Summary How fast a chemical _______________ occurs is called the reaction _______________. Several factors affect the rate of a chemical reaction, including the _______________,

_______________, and _______________ area of reactants, and the presence of a _______________.

What are Acids?1) What is produced when acids are dissolved in water?

2) Write the equation for the reaction that occurs when hydrogen chloride (HCl) is dissolved in water.

Section 12: Properties of Acids

Properties of Acids3) List three properties of acids.

Detecting Acids4) How are indicators used to detect acids?

5) Draw a sketch using colored pencils to show how litmus paper is used to detect acids.

Strength of Acids6) The pH value of a solution represents its concentration of _______________ ions in solution.7) Draw a line from pH value on the left to the corresponding statement on the right.

pH value of 1 neutral solution

pH value of 7 weak acid solution

pH value of 5 strong acid solution

Uses of Acids8) List uses for the following acids:

Sulfuric acid –

Nitric acid –

Phosphoric acid -

Hydrochloric acid –

Lesson Summary Acids are _______________ compounds that produce positive _______________ ions (H+) when

dissolved in _______________. Acids taste _______________, conduct _______________ when dissolved in water, and react with

_______________ to produce _______________ gas. Certain indicator compounds, such as _______________, can be used to detect acids. Acids turn blue

litmus paper _______________. The strength of acids is measured on the _______________. A pH value less than _____ indicates an

acid, and the _______________ the number is, the _______________ the acids. Acids have many important uses, especially in _______________.

What are Bases?1) What is produced when bases are dissolved in water?

2) Write the equation for the reaction that occurs when sodium hydroxide is dissolved in water.

Section 13: Properties of Bases

Properties of Bases3) List three properties of bases.

Detecting Bases4) How are indicators used to detect bases?

5) Draw a sketch using colored pencils to show how litmus paper is used to detect bases.

Strength of Bases6) The pH scale ranges from the numbers _____ to _____.7) Draw a line from pH value on the left to the corresponding statement on the right.

pH value of 9 neutral solution

pH value of 7 weak base solution

pH value of 13 strong base solution

Uses of Bases8) List uses for the following bases:

Potassium hydroxide –

Sodium hydroxide –

Calcium hydroxide -

Aluminum hydroxide –

Lesson Summary Bases are _______________ compounds that produce negative_______________ ions (OH-) when

dissolved in _______________. Bases taste _______________, feel _______________ , and conduct _______________ when

dissolved in water. Indicator compounds such as _______________ can be used to detect bases. Bases turn red litmus

paper _______________. The strength of bases is measured on the _______________. A pH value greater than _____ indicates

a base, and the _______________ the number is, the _______________ the base. Bases have many important uses. For example, they are found in many _______________ products

and used in _______________.

Acids, Bases, and Ions1) An _______________ is a compound that produces positive hydrogen ions and negative nonmetal ions when it dissolves in water. Fill in the blanks below of the chemical reaction that

Section 14: Acid-Base Neutralization

Section 15: Radioactivity

occurs when hydrochloric acid dissolves in water:

2) A _______________ is a compound that produces negative hydroxide ions and positivemetal ions when it dissolves in water. Fill in the blanks below of the chemical reaction thatoccurs when sodium hydroxide dissolves in water:

3) If you were to combine acid and base solution, what products do you think would be produced?

Reactions of Acids and Bases4) What is combined to cause a neutralization reaction?

5) What are the two products of a neutralization reaction?

6) Fill in the products of the following neutralization reaction:

7) Explain how the antacid tablets pictured below relieve acid indigestion in the stomach.

Lesson Summary When acid and base solution react, they produce _______________ and a neutral ionic compound

called _______________. The reaction is called a _______________ reaction.

Introduction1) What is the man in the illustration on the right trying to do?

2) Why doesn’t it work?

Elements and Protons3) For an atom to change from one element to another, the number of ______________ must change.

4) An element that is radioactive must gain or lose ______________.

Radioactive Elements5) From what part of a radioactive atom are particles or energy given off?

6) Elements that have an atomic number above 83 are unstable and radioactive. How do these elements become more stable?

7) Look at the periodic table. Write the symbols of 10 elements that are radioactive.

_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ How Radioactivity Was Discovered

8) For each scientist pictured below, describe their contribution to our knowledge of radioactivity.

Summary ______________ is the ability of an atom to emit charged particles and ______________ from its

nucleus. The charged ______________ and energy are called by the general term ______________. Radioactivity was discovered in _______ by Antoine Henri ______________ when he found that

______________ leaves an image line an X-ray on a photographic plate. Besides uranium, radioactive elements include ______________ and ______________, both of which were discovered by ______________ ______________.

Introduction1) What does the sign at the right indicate?

Marie CurieBecquerel

Section 16: Dangers and Uses of Radiation

Radiation in the Environment2) What is background radiation?

3) Where does background radiation come from? (two sources)

Dangers of Radiation4) Describe the following ways radiation is dangerous:

o Long-term or high-dose exposure:

o Radon:

o Non-living things

Detecting Radiation

5) What is the name of the device pictured to the left?

6) What is the purpose of this instrument?

Using Radiation - Describe three ways radiation is useful:

(1)

(2)

(3)

Summary A low level of ______________ occurs naturally in the environment. This ______________

radiation is generally assumed to be save for ______________ things. Long-term or high-dose exposure to radiation can ______________ living things and damage non-

living things such as ______________. One reason radiation is dangerous is that it generally can’t be detected with the ______________. Radiation has several important uses, including ______________ and ______________ cancer.

Introduction1) The diagram to the right illustrates radioactive decay.

Section 17: Radioactive Decay

Based on the diagram, what happens during radioactive decay?

Introducing Radioactive Decay2) What part of the atom is most involved in radioactive decay?

3) Radioactive decay is a nuclear reaction, not a chemical reaction. Why is it considered a nuclear reaction?

Types of Radioactive Decay4) Fill in the chart below to show the differences in the three types of radioactive decay:

Type Radiation EmittedAlpha decayBeta decay

Gamma decay

It’s Elemental5) How does alpha and beta decay differ from gamma decay?

Dangers of Radioactive Decay 6) Which type of particle is blocked by paper? _______________

7) Which type of particle is blocked by aluminum? _____________

8) Which type is blocked by thick lead? _______________

9) Which type of particle can burn skin but not penetrate it? _________

10) Which type of particle can penetrate and damage skin? __________

11) Which type can damage cells and organs deep in the body?_______

Summary Radioactive _______________ is the process in which unstable _______________ of radioactive

atoms become stable by emitting charged _______________ and _______________. There are three types of radioactive decay: _______________ decay, _______________decay,

and _______________ decay. _______________ and _______________ decay change from element to another, _______________ decay does not.

Radioactive decay can _______________ living things. _______________ decay is the least damaging, and _______________ decay is the most damaging.

Introduction1) How are radioactive isotopes a little like cutting a sheet of paper in half over and over?

Section 18: Radioactive Half-life

What is a Radioactive Isotope?2) A radioactive isotope, or radioisotope are atoms with unstable _______________.

3) What happens to the amount of the original radioisotope in a sample as it decays?

Rate of Radioactive Decay4) Is the rate of decay for a radioisotope constant or does it change over time?

5) Explain the unit half-life.

Half-Life Examples - The half-life of Carbon 14 is 5,700 years. Use the graph to answer the questions.

6) How many years does it take for ½ of the original sample of Carbon 14 to decay?

7) What percentage of the original sample of Carbon 14 remains after 11,400 years?

8) How many half-lives have occurred after 28,500 years have passed?

Variation in Half-Lives9) Half-live time vary greatly for different radioisotopes. Fill in the chart below.

Radioisotope Half-lifeUranium-238Potassium-40

Carbon-14Hydrogen-3Radon-222

Polonium-214

Summary A _______________ decays and changes to a different _______________ at a certain constant rate

called the _______________. This is the length of time it takes for _______________ of a given amount of the radioisotope to _______________.

Different radioisotopes may vary greatly in their _______________ of decay. The more _______________ the nuclei are, the _______________ they decay.