Chapter Menu Section 4.1Section 4.1The Variety of Compounds Section 4.2 Section 4.2 How Elements...

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Section 4.1 The Variety of Compounds

Section 4.2 How Elements Form Compounds

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Section 4.1

The Variety of Compounds

• Distinguish the properties of compounds from those of the elements of which they are composed.

• Compare and contrast the properties of sodium chloride, water, and carbon dioxide.

• Predict whether two elements will react to form a compound.

Section 4.1

The Variety of Compounds

chemical property: a property that can be observed when there is a change in the composition of a substance.

The properties of compounds differ from the properties of the elements that form the compounds.

Section 4.1

Table Salt (NaCl)

• Table salt, or sodium chloride, is so abundant on Earth, it is used to manufacture the elements sodium and chloride.

Section 4.1

Table Salt (cont.)

• Properties of table salt

– white, cubed crystals at room temperature

– crystals are hard but brittle and do not conduct electricity

– When salt is heated to a temperature of about 800°C, it melts and forms liquid salt which does conduct electricity.

Section 4.1

Table Salt (cont.)

• Salt easily dissolves in water—the resulting solution is an excellent conductor of electricity.

• Salt does not react readily with other substances.

Section 4.1

Table Salt (cont.)

• Properties of sodium

– shiny, silvery-white, soft, solid metallic element that melts when heated above 98°C

– Because of its high reactivity, the free element sodium is never found in the environment but is always found combined with other elements.

Section 4.1

Table Salt (cont.)

• Properties of chlorine

– pale green, poisonous gas with a choking odor that kills living cells and is slightly soluble in water

– it is a nonmetal that must be cooled to

-34°C before it turns to a liquid

– highly reactive and used for many industrial processes

Section 4.1

Carbon Dioxide

• Carbon dioxide is a gas that is an important link between the plant and animal world.

Section 4.1

Carbon Dioxide (cont.)

• Properties of carbon dioxide

– colorless, odorless, and tasteless gas at room temperature

– When cooled below –80°C, carbon dioxide gas changes directly to a white solid, known as dry ice, without first becoming a liquid. (This is called deposition.)

– is soluble in water but a weak conductor of electricity

Section 4.1


– used to put out fires since it does not support burning

– it is necessary for photosynthesis

Section 4.1


• Properties of carbon

– nonmetal that is fairly unreactive at room temperature but reacts with many other elements at higher temperatures

– excellent source of heat

– the majority of compounds that make up living things contain carbon

Section 4.1


• Properties of oxygen

– a nonmetal that is a colorless, odorless, and tasteless gas

– becomes a liquid at –183°C and is slightly soluble in water

– is the most abundant element in the Earth’s crust, but typically combined with other elements

– more reactive than carbon

Section 4.1


Section 4.1

Water

• Dihydrogen monoxide, better known as water, covers approximately 70 percent of Earth’s surface and also makes up about 70 percent of the mass of the average human body.

Section 4.1

Water (cont.)

• Properties of water

– occurs in Earth’s environment in all three common states(solid, liquid, and gas)

– freezes into a solid at 0°C and becomes a gas at 100°C

– does not conduct electricity in any of its states

– universal solvent

Section 4.1

Water (cont.)

– stable compound that does not break down under normal circumstances and does not react with many other substances

– nearly all the chemical reactions in the human body and many important reactions on Earth occur in an aqueous solution

Section 4.1

Water (cont.)

• Properties of hydrogen

– colorless, odorless, and tasteless gas which is the lightest and most abundant element in the universe

– usually classified as a nonmetal that does not conduct electricity and is only slightly soluble in water

Section 4.1

Water (cont.)

– reactive element that usually occurs in a variety of compounds

– turns into a liquid at –253°C

Section 4.1

Using clues to make a case

• Macroscopic properties provide clues about what happens on the submicroscopic level.

Section 4.1

Section Assessment

The majority of compounds that make up living things contain ___.

A. oxygen

B. carbon

C. sulfur

D. sodium

Section 4.1

Section Assessment

Rusting is a prime example of which element’s reactivity?

A. iron

B. carbon

C. oxygen

D. hydrogen

End of Section 4.1

Section 4.2

How Elements Form Compounds

• Model two types of compound formation: ionic and covalent at the submicroscopic level.

• Demonstrate how and why atoms achieve chemical stability by bonding.

• Compare, using examples, the effect of covalent and ionic bonding on the physical properties of compounds.

Section 4.2


valence electron: an electron in the outermost energy level of an atom

Section 4.2


octet rule

noble gas configuration

ion

ionic compound

ionic bond

crystal

covalent bond

covalent compound

molecule

electrolyte

interparticle force

Compounds form when electrons in atoms rearrange to achieve a stable configuration.

Section 4.2

Atoms Collide

• When substances react, particles of the substances must collide.

• Reactions between atoms involve only their electron clouds.

Section 4.2

Chemical Stability

• Group 18 elements, also known as the noble gases, almost completely lack chemical reactivity.

• Each noble gas has eight valence electrons, except for helium, which has two.

Section 4.2

Chemical Stability (cont.)

• The octet rule is the model of chemical stability that states that atoms become stable by having eight electrons in their outer energy level except for some of the smallest atoms, which have only two electrons (duet rule).

Section 4.2


• A noble gas configuration is the state of an atom achieved by having the same valence electron configuration as a noble gas atom, which is the most stable configuration.

Section 4.2


Section 4.2

Ways to Achieve Stability

• When elements combine, they form either ions or molecules.

• Atoms try to form the octet (or duet) by gaining or losing valence electrons.

Section 4.2

Ways to Achieve Stability (cont.)

• An ion is an atom or group of combined atoms that has a charge because of the loss or gain of electrons.

• A compound that is composed of ions is called an ionic compound.

Section 4.2


Section 4.2


• The strong attractive force between ions of opposite charge is called an ionic bond.

• A crystal is a regular, repeating arrangement of atoms, ions, or molecules.

• Solid substances are composed of crystals.

Section 4.2


• In order for a solid, such as sodium chloride, to melt, its temperature must be raised until the motion of the particles overcomes the attractive forces and the crystal organization breaks down.

Section 4.2


• Chemical formulas indicate what elements make up the compound and how many atoms of each element are present in one unit of the compound.

Section 4.2


Section 4.2


• Atoms can also share valence electrons to achieve a stable octet.

Section 4.2


• The attraction of two atoms for a shared pair of electrons is called a covalent bond.

• A compound whose atoms are held together by covalent bonds is a covalent compound.

• A molecule is an uncharged group of two or more atoms held together by covalent bonds.

Section 4.2


• Two nonmetallic elements usually achieve stability by sharing electrons to form a covalent compound.

• If the reacting atoms are a metal and a nonmetal, they are much more likely to transfer electrons and form an ionic bond.

Section 4.2


• In addition to double bonds, atoms can form triple bonds.

Section 4.2

How do ionic and covalent compounds compare?

• The strong attractions among positive and negative ions in an ionic compound result in a strong, three-dimensional crystal structure that is hard, brittle, and must be heated to high temperatures to melt.

Section 4.2

How do ionic and covalent compounds compare? (cont.)

• Ionic compounds are electrolytes, compounds that conduct electricity when melted or dissolved in water.

• The attractive forces between molecules of a covalent compound are weak because the molecules themselves have no charge.

Section 4.2

How do ionic and covalent compounds compare? (cont.)

• Interparticle forces, or the forces between particles that make up a substance, are the key to determining the state of matter of a substance.

• The difference in strength of the interparticle forces in covalent compounds compared to ionic compounds explains differences in their properties.

Section 4.2

Section Assessment

What determines the state of matter of a substance?

A. interparticle forces

B. ionic bonds

C. covalent bonds

D. the ability to conduct electricity

Section 4.2

Section Assessment

All ionic compounds are ___ at room temperature.

A. solids

B. liquids

C. gases

End of Section 4.2

Resources Menu

Chemistry Online

Study Guide

Chapter Assessment

Standardized Test Practice

Image Bank

Concepts in Motion

http://www.glencoe.com/

Study Guide 1

Key Concepts

• When compounds form, they have properties that differ greatly from the properties of the elements of which they are made.

• Atoms combine in different ways to form different kinds of compounds.

• The properties of compounds differ widely because of differences in what happens to their constituent atoms when they form.

• Macroscopic properties provide clues about what happens on the submicroscopic level.

Study Guide 2

Key Concepts

• Atoms become stable by reacting to achieve the outer-level electron structure of a noble gas (Group 18).

• To achieve stability, some atoms transfer electrons to another atom, thus forming charged ions of opposite charge. The ions attract each other and form an ionic compound.

• Some atoms share electrons to form covalent compounds.

• Two atoms can share more than one pair of electrons.

• In ionic compounds, the interparticle forces are attractions between ions of opposite electric charge. They are much stronger than the interparticle forces between molecules of covalent compounds.

Chapter Assessment 1

Photosynthesis is probably the most significant chemical reaction of ___.

A. oxygen

B. carbon

C. carbon dioxide

D. sodium chloride


In their elemental state, which group has a complete octet of valence electrons?

A. alkali metals

B. alkaline earth metals

C. halogens

D. noble gases


What forms when a metallic element and a nonmetallic element are combined?

A. ionic bond

B. covalent bond

C. covalent compound

D. noble gas configuration


What is another name for a molecular bond?

A. molecule

B. ionic bond

C. covalent bond

D. covalent compound


Why are solid ionic compounds poor conductors of electricity?

A. They are nonmetals.

B. They have electrons that cannot flowfreely.

C. They are electrolytes.

D. Solids do not conduct electricity.

STP 1

What is the electrostatic charge holding two ions together?

A. ionic bond

B. covalent bond

C. covalent compound

D. crystal lattice bond

STP 2

Why are the attractive forces between molecules of a covalent compound weak?

A. The molecules have no charge.

B. The molecules form ionic bonds.

C. interparticle forces

D. They lack electrolytes.

STP 3

A(n) ___ is a regular, repeating arrangement of atoms, ions, and molecules.

A. pattern

B. crystal

C. lattice

D. octet

STP 4

Which element would not be commonly used in a neon light display?

A. hydrogen

B. argon

C. helium

D. radon

STP 5

A(n) ___ is an uncharged group of two or more atoms held together by covalent bonds.

A. ion

B. crystal

C. electrolyte

D. molecule

IB Menu

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CIM

Figure 4.17 Na/Cl ionic bond

Figure 4.24 Electrolytes

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