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Lesson 1: How Atoms Form Compounds

Lesson 2: Forming Solids

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compound

chemical formula

molecule

chemical bond

ionic bond

valence

covalent bond

5.1 How Atoms Form Compounds

What is a compound?

• A compound is a pure substance that contains two or more elements.

• Compounds are chemical combinations of elements with properties that are different from the elements that formed them.

5.1 How Atoms Form Compounds

Chemical Formulas for Compounds• A chemical formula contains atomic symbols and subscripts to show the

elements and the number of atoms of each element in the compound.

5.1 How Atoms Form Compounds

Describing Compounds• A water molecule, or H2O, is two hydrogen atoms bonded to

one oxygen atom.

• The subscript number shows how many atoms the element are in the compound.

• A molecule is a neutral particle that forms as a result of electron sharing.

5.1 How Atoms Form Compounds

How can a molecule model be built?

Describing Compounds (cont.)

• The chemical formula for sucrose, C12H22O11, includes all the atoms in one molecule.

5.1 How Atoms Form Compounds

Formulas and the Law of Definite Proportion• A pure compound will always contain the same elements in the same proportion

by mass.

5.1 How Atoms Form Compounds

Compounds and Their Elements• Compounds have different properties than the

elements that make them up.

– Sodium chloride is table salt.

– Sodium is a soft metal.

– Chlorine is a greenish-yellow gas.

5.1 How Atoms Form Compounds

Ionic Bonds and Ionic Compounds• A chemical bond is a force that holds atoms

together in a compound.

• An ionic bond is an electrical attraction between positively and negatively charged ions in an ionic compound.

5.1 How Atoms Form Compounds

Ionic Bonds—Transferring Electrons• An atom can become charged by transferring one or

more electrons to another atom.

• Both atoms become charged particles, or ions.

5.1 How Atoms Form Compounds

Ionic Bonds—Transferring Electrons• A lithium atom gives up an electron to a fluorine

atom.

• The result is a positively charged lithium ion and a negatively charged fluoride ion.

(cont.)

5.1 How Atoms Form Compounds

Ionic Bonds—Transferring Electrons• The two ions have opposite charges and are

attracted to each other.

(cont.)

• Lithium fluoride is the simplest type of compound, made only of two elements and known as a binary compound.

5.1 How Atoms Form Compounds

Ionic Bonds—Transferring Electrons(cont.)

5.1 How Atoms Form Compounds

Ionic Compounds• Elements in the same column on the periodic table form

a group.

• Metals in Group 1 can transfer 1 electron and will become +1 ions.

• Non-metals in Group 17 can gain an electron to form −1 ions.

• When a positive ion from Group 1 and a negative ion from Group 17 combine, a salt like sodium chloride forms.

5.1 How Atoms Form Compounds

Other Binary Ionic Compounds• Group 2 elements are also metals and can lose 2

electrons and form ions with a +2 charge.

• Elements in Group 16 can gain 2 electrons and form ions with a −2 charge.

5.1 How Atoms Form Compounds

Other Binary Ionic Compounds (cont.)

• Magnesium can transfer one electron to each of 2 Fluorine atoms to form magnesium fluoride (MgF2).

5.1 How Atoms Form Compounds

Properties of Ionic Compounds

• Usually solids at room temperature

• Brittle and break apart easily

• Have high melting and boiling points

• Many dissolve in water

5.1 How Atoms Form Compounds

Diagramming Electrons—Lewis Dot Diagrams

• A Lewis dot diagram is a system to represent atoms and their electrons.

• You must know the number of valence electrons an atom has.

• Valence electrons are the electrons in the outermost energy level.

5.1 How Atoms Form Compounds

Diagramming Electrons—Lewis Dot Diagrams

5.1 How Atoms Form Compounds

Diagramming Electrons—Lewis Dot Diagrams (cont.)

Ions and Noble Gases• Groups 2–12 of the periodic table are metals and the

valence number can vary.

• Elements in Group 18 are the noble gases.

• The noble gases are stable because their outer energy levels are filled.

• Elements that are stable rarely react to form compounds.

5.1 How Atoms Form Compounds

Noble Gas Structure by Gaining Electrons

• Chlorine can achieve noble gas structure by filling its outer energy levels.

• Argon is the nearest noble gas to chlorine.

• Chlorine can become more stable by gaining one electron and forming the chloride ion Cl–.

5.1 How Atoms Form Compounds

Noble Gas Structure by Losing Electrons• Magnesium can achieve the electron structure of neon, the nearest noble gas

on the periodic table.

• Magnesium can lose two electrons to form the stable ion Mg2+.

5.1 How Atoms Form Compounds

Covalent Bonds—Sharing Electrons

• Ionic bonds form when electrons are transferred.

• Some elements need to gain or lose too many electrons.

• A covalent bond is a chemical bond formed when atoms share electrons.

5.1 How Atoms Form Compounds

Covalent Bonds—Sharing Electrons

• Carbon has 4 valence electrons.

• Too much energy is needed for carbon to easily gain or lose 4 electrons.

(cont.)

5.1 How Atoms Form Compounds

Covalent Bonds—Sharing Electrons

• Covalent bonds form by sharing electrons.(cont.)

• Elements that are close together on the periodic table are more likely to share electrons in a covalent bond than to transfer electrons.

• Organic compounds are covalent compounds containing carbon atoms and are important for living organisms.

5.1 How Atoms Form Compounds

Covalent Bonds—Sharing Electrons(cont.)

5.1 How Atoms Form Compounds

Properties of Covalent Compounds• Can be solids, liquids, or gases at

room temperature

• Usually have lower melting and boiling points than ionic compounds

• Do not usually separate in water

• Most do not conduct electricity

5.1 How Atoms Form Compounds

Single Covalent Bonds

• Hydrogen has one unpaired electron.

• Two hydrogen atoms share their single electrons to form a pair.

• The shared pair of electrons is a single covalent bond, which holds the hydrogen molecule H2 together.

5.1 How Atoms Form Compounds

Double and Triple Bonds• Some atoms may form stronger bonds by sharing

more than one pair of electrons.

• A double bond has two pairs of shared electrons and is stronger than a single bond.

• A triple bond has three pairs of shared electrons and is stronger than a double bond.

5.1 How Atoms Form Compounds

Lesson 1 Review

Bromine is in Group 17. How many electrons does bromine need to gain or lose to obtain a noble gas structure?

A gain one electron

B gain two electrons

C lose one electron

D lose two electrons

5.1 How Atoms Form Compounds

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1. A

2. B

3. C

4. D

Lesson 1 Review

Which element can form a negative ion?

A carbon

B magnesium

C chlorine

D lithium

5.1 How Atoms Form Compounds

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1. A

2. B

3. C

4. D

Lesson 1 Review

What holds two elements together in an ionic bond?

A covalent bonds from shared electrons

B electron clouds combining

C unpaired electrons attracting each other

D opposite charges on negative and positive ions

5.1 How Atoms Form Compounds

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1. A

2. B

3. C

4. D

End of Lesson 1

metal

metallic bond

malleability

ductility

5.2 Forming Solids

crystal

unit cell

polymer

monomer

Metals• Metals are elements that are usually shiny, good conductors

of electricity and heat, and solid at room temperature.

5.2 Forming Solids

Metallic Bonds• A metallic bond is formed when many metal atoms

share their pooled electrons.

• Metal atoms can bond to atoms of the same element, or to other metals.

5.2 Forming Solids

Bonding and Properties• Metals are good conductors because their electrons

move freely.

• Metals can be hammered into sheets or pulled into wires without breaking.

5.2 Forming Solids

Metal Atoms and Patterns• Metal atoms combine in a regular pattern in which

some electrons are free to move about.

5.2 Forming Solids

Physical Properties of Metals• Malleability is the ability of a metal to be hammered or

rolled into sheets.

• Ductility is the ability of a substance to be pulled into a wire.

5.2 Forming Solids

Crystals• A crystal is a regular, repeating arrangement of

atoms, ions, or molecules.

5.2 Forming Solids

• Crystals are formed from repeating patterns.

• A unit cell is the smallest repeating pattern that shows how atoms, ions, or molecules are arranged in a crystal.

What is a polymer?• A polymer is a covalent compound made up of many

repeating units linked together in a chain.

• A monomer is a single molecule that forms a link in a polymer chain.

• Many hundreds of monomers link together to form a solid polymer.

5.2 Forming Solids

Synthetic Polymers• Synthetic polymers, such as polyethylene, are

polymers manufactured by humans.

5.2 Forming Solids

Natural Polymers• All living cells must contain three important kinds of natural

organic polymers—proteins, carbohydrates, and nucleic acids.

5.2 Forming Solids

Natural Polymers (cont.)

• Amino acid monomers join together to form a protein.

• Protein and carbohydrate polymers shown with their monomers.

5.2 Forming Solids

Lesson 2 Review

What holds carbohydrates together?

A ionic bonds

B metallic bonds

C covalent bonds

D electron clouds

5.2 Forming Solids

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1. A

2. B

3. C

4. D

Lesson 2 Review

Which of the following is the most malleable?

A crystal

B polymer

C metal

D monomer

5.2 Forming Solids

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1. A

2. B

3. C

4. D

Lesson 2 Review

A(n) ____ is the smallest repeating pattern in a crystal.

A monomer

B polymer

C metallic bond

D unit cell

5.2 Forming Solids

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1. A

2. B

3. C

4. D

End of Lesson 2

Chapter Resources Menu

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Chapter Assessment

California Standards Practice

Concepts in Motion

Image Bank

Science Online

Interactive Table

Virtual Lab

How many dots are in a Lewis dot diagram for the Group 1 element lithium?

A 1

B 2

C 3

D 4

Chapter Assessment 1

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1. A

2. B

3. C

4. D

Which is an example of a natural polymer?

A sodium chloride

B polyethylene

C polysaccharide

D quartz

Chapter Assessment 2

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1. A

2. B

3. C

4. D

Why are noble gases unlikely to form compounds with other elements?

A They form ionic bonds.

B They have 8 valence electrons.

C They form covalent bonds.

D Their outer energy levels are not filled with electrons.

Chapter Assessment 3

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1. A

2. B

3. C

4. D

Compounds sharing electrons are held together by ____.

A ionic bonds

B covalent bonds

C metallic bonds

D polymer chains

Chapter Assessment 4

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1. A

2. B

3. C

4. D

A polymer is made up of many repeating monomers held together by ____.

A metallic bonds

B polymer chains

C ionic bonds

D covalent bonds

Chapter Assessment 5

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1. A

2. B

3. C

4. D

Which elements are least likely to react with other elements?

A metals

B Group 17 elements

C Group 16 elements

D Noble gases

CA Standards Practice 1

SCI 3.b

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1. A

2. B

3. C

4. D

In the ionic compound magnesium oxide (MgO), how many electrons did oxygen give magnesium?

A 1

B 2

C 3

D none of the above

CA Standards Practice 2

SCI 3.b

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1. A

2. B

3. C

4. D

Metals are good conductors because ____.

A their electrons move freely

B their protons move freely

C they have ionic bonds

D none of the above

CA Standards Practice 3

SCI 3.c

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1. A

2. B

3. C

4. D

Noble gases are in which group on the periodic table?

A 1

B 2

C 17

D 18

CA Standards Practice 4

SCI 3.f

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1. A

2. B

3. C

4. D

Which property of copper allows it to be pulled into wires?

A ductility

B malleability

C conductivity

D luster

CA Standards Practice 5

SCI 7.c

0% 0%0%0%

1. A

2. B

3. C

4. D

Concepts in Motion 1

Concepts in Motion 2

Image Bank

Interactive Table

End of Resources