Chapter 6 Chemical Bonds. 6.1 Ionic Bonding Chemical properties, such as reactivity, depend on an...

Chapter 6Chapter 6

Chemical BondsChemical Bonds

Chemical BondsChemical Bonds 6.1 Ionic Bonding6.1 Ionic Bonding

6.1 Ionic Bonding6.1 Ionic Bonding

Chemical properties, such as reactivity, Chemical properties, such as reactivity, depend on an element’s electron depend on an element’s electron configuration.configuration.


Stable Electron ConfigurationsStable Electron Configurations

The highest occupied energy level of a The highest occupied energy level of a noble gas atom is filled. noble gas atom is filled.

When the highest occupied level is filled When the highest occupied level is filled with electrons, the atom is stable and not with electrons, the atom is stable and not likely to react. likely to react.

The chemical properties of an element The chemical properties of an element depend on the number of valence depend on the number of valence electrons. electrons.


An electron dot diagram is a model of an An electron dot diagram is a model of an atom in which each dot represents a atom in which each dot represents a valence electron. valence electron.

The symbol in the center represents the The symbol in the center represents the nucleus and all the other electrons in the nucleus and all the other electrons in the atom. atom.


Ionic BondsIonic Bonds

Elements that do not have complete sets Elements that do not have complete sets of valence electrons tend to react. of valence electrons tend to react.

By reacting, they achieve electron By reacting, they achieve electron configurations similar to noble gases.configurations similar to noble gases.

Some elements achieve stable electron Some elements achieve stable electron configurations through the transfer of configurations through the transfer of electrons between atoms.electrons between atoms.


Transfer of ElectronsTransfer of Electrons

When sodium reacts with chlorine an When sodium reacts with chlorine an electron is transferred from sodium to electron is transferred from sodium to chlorine. chlorine.

Each atom ends up with a more stable Each atom ends up with a more stable electron arrangement.electron arrangement.


Formation of IonsFormation of Ions

When an atom gains or loses an electron, When an atom gains or loses an electron, the number of protons is no longer equal the number of protons is no longer equal to the number of electrons and the atom is to the number of electrons and the atom is not neutral. not neutral.

An atom that has a net positive or negative An atom that has a net positive or negative charge is called an ion. charge is called an ion.


An ion with a negative charge is an anion. An ion with a negative charge is an anion.

Anions form when atoms gain electrons. Anions form when atoms gain electrons.

Anions are named by using the element’s Anions are named by using the element’s root name plus –root name plus –ideide. .

For example ClFor example Cl−− is called a is called a chloride chloride ion.ion.


The elements that lose electrons become The elements that lose electrons become positive ions, called cations. positive ions, called cations.

Cations retain the same name as the Cations retain the same name as the element. element.

For example, NaFor example, Na++ is the sodium ion. is the sodium ion.


Formation of Ionic BondsFormation of Ionic Bonds

A particle with a negative charge will A particle with a negative charge will attract a particle with a positive charge.attract a particle with a positive charge.

When an anion and a cation are close When an anion and a cation are close together, a chemical bond forms between together, a chemical bond forms between them. them.

A chemical bond is the force that holds A chemical bond is the force that holds atoms or ions together as a unit. atoms or ions together as a unit.

An ionic bond is the force that holds An ionic bond is the force that holds cations and anions togethercations and anions together


Ionization EnergyIonization Energy

Cations form when electrons gain enough Cations form when electrons gain enough energy to escape from atoms. energy to escape from atoms.

The energy allows electrons to overcome The energy allows electrons to overcome the attraction of the protons in the nucleus.the attraction of the protons in the nucleus.

The amount of energy used to remove an The amount of energy used to remove an electron is called ionization energy. electron is called ionization energy.

The lower the ionization energy, the easier The lower the ionization energy, the easier it is to remove an electron. it is to remove an electron.


Ionization energies tend to increase from Ionization energies tend to increase from left to right across a period. left to right across a period.

It takes more energy to remove an It takes more energy to remove an electron from a nonmetal than from a electron from a nonmetal than from a metal in the period. metal in the period.

Ionization energies tend to decrease from Ionization energies tend to decrease from top of a group to the bottom.top of a group to the bottom.


Ionic CompoundsIonic Compounds

Compounds that contain ionic bonds are Compounds that contain ionic bonds are ionic compounds. ionic compounds.

A chemical formula is annotation that A chemical formula is annotation that shows what elements a compound shows what elements a compound contains and the ratio of the atoms or ions contains and the ratio of the atoms or ions in the compound.in the compound.


Subscripts are used to show the relative Subscripts are used to show the relative numbers of atoms of the elements numbers of atoms of the elements present. present.

If there is only one atom of an element If there is only one atom of an element present, no subscript is used.present, no subscript is used.

MgClMgCl22


Crystal LatticesCrystal Lattices

A chemical formula does not tell how the A chemical formula does not tell how the ions are arranged in a compound. ions are arranged in a compound.

Figure 5 shows that NaCl is arranged in a Figure 5 shows that NaCl is arranged in a cubic pattern. cubic pattern.

Solids whose particles are arranged in a Solids whose particles are arranged in a lattice structure are called crystals. lattice structure are called crystals.

The arrangement of ions depends on the The arrangement of ions depends on the ratio of ions and their relative sizes. ratio of ions and their relative sizes.


Crystals are classified into groups based Crystals are classified into groups based on the shape of their crystals. on the shape of their crystals.

Crystals are classified into seven different Crystals are classified into seven different systems distinguished by the angles at systems distinguished by the angles at which the faces meet and the length of the which the faces meet and the length of the edges on the face.edges on the face.


Properties of Ionic CompoundsProperties of Ionic CompoundsThe properties of an ionic compound can The properties of an ionic compound can be explained the strong attractions among be explained the strong attractions among ions within a crystal lattice. ions within a crystal lattice.

The arrangement of particles in a The arrangement of particles in a substance is the result of two opposing substance is the result of two opposing forces forces

– the attractions among particles in the the attractions among particles in the substancesubstance

– the kinetic energy of the particles. the kinetic energy of the particles.


The stronger the attractions among The stronger the attractions among the particles, the more kinetic energy the particles, the more kinetic energy the particles must have before they the particles must have before they can separate.can separate.

Chemical BondsChemical Bonds 6.2 Covalent Bonding6.2 Covalent Bonding

6.2 Covalent Bonding6.2 Covalent Bonding

A transfer of electrons does not tend to A transfer of electrons does not tend to occur between nonmetal atoms.occur between nonmetal atoms.


Sharing ElectronsSharing Electrons

A covalent bond is a chemical bond in A covalent bond is a chemical bond in which two atoms share a pair of valence which two atoms share a pair of valence electrons. electrons.

When two atoms share a one pair of When two atoms share a one pair of electrons, the bond is called a single bond. electrons, the bond is called a single bond.

Covalent BondsCovalent Bonds


Figure 9 shows four different ways to Figure 9 shows four different ways to represent a covalent bond. represent a covalent bond.

The electron cloud model and space filling The electron cloud model and space filling model show that orbitals of atoms overlap model show that orbitals of atoms overlap when a covalent bond forms. when a covalent bond forms.


Molecules of ElementsMolecules of Elements

A molecule is a neutral group of atoms A molecule is a neutral group of atoms that are joined together by one or more that are joined together by one or more covalent bonds. covalent bonds. The attractions between the shared The attractions between the shared electrons and the protons in each nucleus electrons and the protons in each nucleus hold the atoms together in a covalent hold the atoms together in a covalent bond. bond. Many nonmetal elements exist as diatomic Many nonmetal elements exist as diatomic molecules. molecules.


Multiple Covalent BondsMultiple Covalent Bonds

When the atoms in a NWhen the atoms in a N22 molecule share molecule share

three pairs of electrons, each atom has three pairs of electrons, each atom has eight valence electrons. eight valence electrons.

Each pair of shared electrons is Each pair of shared electrons is represented by a long dash, N≡N. represented by a long dash, N≡N.


When two atoms share three pairs of When two atoms share three pairs of electrons, the bond is called a triple bond. electrons, the bond is called a triple bond.

When two atoms share two pairs of When two atoms share two pairs of electrons, the bond is called a double electrons, the bond is called a double bond.bond.


Unequal Sharing of ElectronsUnequal Sharing of Electrons

In general, elements on the right of the In general, elements on the right of the periodic table have a greater attraction for periodic table have a greater attraction for electrons than the elements on the left.electrons than the elements on the left.In general, elements at the top of a group In general, elements at the top of a group have a greater attraction for electrons than have a greater attraction for electrons than elements at the bottom of a group.elements at the bottom of a group.Fluorine has the strongest attraction for Fluorine has the strongest attraction for electrons and is the most reactive electrons and is the most reactive nonmetal. nonmetal.


Polar Covalent BondsPolar Covalent Bonds

In a molecule of an element, the atoms In a molecule of an element, the atoms that form covalent bonds have the same that form covalent bonds have the same ability to attract an electron. ability to attract an electron.

In a molecule of a compound, electrons In a molecule of a compound, electrons may not be shared equally. may not be shared equally.


Figure 11 shows models of the molecules Figure 11 shows models of the molecules that form when hydrogen reacts with that form when hydrogen reacts with chlorine. chlorine.

A chlorine atom has a greater attraction for A chlorine atom has a greater attraction for electrons than a hydrogen atom does. electrons than a hydrogen atom does.


A covalent bond in which electrons are not A covalent bond in which electrons are not shared equally is called a polar covalent shared equally is called a polar covalent bond. bond.

When atoms form a polar covalent bond, When atoms form a polar covalent bond, the atom with the greater attraction for the atom with the greater attraction for electrons has a partial negative charge. electrons has a partial negative charge.

The other atom has a partial positive The other atom has a partial positive charge.charge.


Polar and Nonpolar MoleculesPolar and Nonpolar Molecules

The type of atoms in a molecule and its The type of atoms in a molecule and its shape are factors that determine whether shape are factors that determine whether a molecule is polar or nonpolar.a molecule is polar or nonpolar.


Attraction Between MoleculesAttraction Between Molecules

In a molecular compound, there are forces In a molecular compound, there are forces of attraction between molecules. of attraction between molecules.

Attractions between polar molecules are Attractions between polar molecules are stronger than attractions between stronger than attractions between nonpolar molecules.nonpolar molecules.

Chemical BondsChemical Bonds 6.3 Naming Compounds and Writing Formulas6.3 Naming Compounds and Writing Formulas

6.3 Naming Compounds and 6.3 Naming Compounds and Writing FormulasWriting Formulas

Chemists use a system for naming Chemists use a system for naming compounds that is based on composition. compounds that is based on composition.

The formula of a compound serves as a The formula of a compound serves as a reminder of the composition of the reminder of the composition of the compound. compound.


Describing Ionic CompoundsDescribing Ionic Compounds

The name of an ionic compound must The name of an ionic compound must distinguish the compound from other ionic distinguish the compound from other ionic compounds containing the same compounds containing the same elements. elements.

The formula of an ionic compound The formula of an ionic compound describes the ratio of the ions in the describes the ratio of the ions in the compound. compound.


Binary Ionic CompoundsBinary Ionic Compounds

A compound made from only two elements A compound made from only two elements is a binary compound. is a binary compound.

The names have a predictable pattern: the The names have a predictable pattern: the name of the cation followed by the name name of the cation followed by the name of the anion. of the anion.

The name for the cation is the name of the The name for the cation is the name of the metal without any change. metal without any change.


The name for the anion uses part of the The name for the anion uses part of the name of the nonmetal with the suffix name of the nonmetal with the suffix ideide. .

Figure 16 lists some common anions. Figure 16 lists some common anions.


Metals with Multiple IonsMetals with Multiple Ions

The alkali metals, alkaline earth metals, The alkali metals, alkaline earth metals, and aluminum form ions with positive and aluminum form ions with positive charges equal to the group number. charges equal to the group number. Many transition metals form more than Many transition metals form more than one type of ion. one type of ion. When a metal forms more than one ion, When a metal forms more than one ion, the name of the ion contains a Roman the name of the ion contains a Roman numeral to indicate the charge on the ion. numeral to indicate the charge on the ion. Figure 17 lists some metal cations. Figure 17 lists some metal cations.


For example, the formula for “copper (I) For example, the formula for “copper (I) oxide” is Cuoxide” is Cu22O O

– because it takes two Cubecause it takes two Cu++ ions to balance the ions to balance the charge on an Ocharge on an O2−2− ion. ion.

The formula for “copper (II) oxide” is CuO The formula for “copper (II) oxide” is CuO – because it takes only one Cubecause it takes only one Cu2+2+ to balance the to balance the

charge on an Ocharge on an O2−2− ion. ion.


Polyatomic IonsPolyatomic Ions

A covalently bonded group of atoms with a A covalently bonded group of atoms with a charge that acts as a unit is called a charge that acts as a unit is called a polyatomic ion. polyatomic ion. For example, iron (III) hydroxide is For example, iron (III) hydroxide is Fe(OH)Fe(OH)33. .

The subscript indicates there are three The subscript indicates there are three OHOH ions in the formula. ions in the formula. Figure 19 shows some of the common Figure 19 shows some of the common polyatomic ions. polyatomic ions.


Writing Formulas for Ionic Writing Formulas for Ionic CompoundsCompounds

If you know the name of an ionic If you know the name of an ionic compound, you can write its formula. compound, you can write its formula.

Write the symbol of the cation first, Write the symbol of the cation first, followed by the symbol of the anion. followed by the symbol of the anion.


Use subscripts to show the ratio of the Use subscripts to show the ratio of the ions in the compound.ions in the compound.

Oxidation numbers show how many Oxidation numbers show how many electrons are lost, gained or shared by electrons are lost, gained or shared by atoms.atoms.

The total charges on the cations and The total charges on the cations and anions anions mustmust add up to zero. add up to zero.


Describing Molecular Describing Molecular CompoundsCompounds

Like ionic compounds, molecular Like ionic compounds, molecular compounds have names that identify compounds have names that identify specific compounds. specific compounds.


The name and formula of a molecular The name and formula of a molecular compound describe the type and number compound describe the type and number of atoms in a molecule of the compound. of atoms in a molecule of the compound.


Naming Molecular CompoundsNaming Molecular Compounds

A general rule is that the most metallic A general rule is that the most metallic element appears first in the name. element appears first in the name.

If both elements are in the same group, If both elements are in the same group, the more metallic element is closer to the the more metallic element is closer to the bottom of the group. bottom of the group.

The name of the second element is The name of the second element is changed to end in the suffix changed to end in the suffix ideide. .


Figure 20 shows the Greek prefixes used Figure 20 shows the Greek prefixes used in naming molecular compounds. in naming molecular compounds.

Example: NExample: N22OO44 is is

dinitrogen tetraoxide. dinitrogen tetraoxide.


Writing Molecular FormulasWriting Molecular Formulas

Writing the formula for a molecular Writing the formula for a molecular compound involves writing the symbols for compound involves writing the symbols for the elements in the order they appear in the elements in the order they appear in the name. the name.

Prefixes indicate the number of atoms of Prefixes indicate the number of atoms of each in the molecule and are used as each in the molecule and are used as subscripts in the formula. subscripts in the formula.

For example: diphosphorus tetraflourideFor example: diphosphorus tetraflouride PP22FF44


If an ion ends in If an ion ends in ide,ide, it is monatomic. it is monatomic.– Sulfide is SSulfide is S2-2-

If ion ends in If ion ends in ite ite or or ateate it is a polyatomic it is a polyatomic ion and contains oxygen (oxyanions)ion and contains oxygen (oxyanions)– Sulfate is SOSulfate is SO44

2-2-

Chemical BondsChemical Bonds 6.4 The Structure of Metals6.4 The Structure of Metals

6.4 The Structure of Metals6.4 The Structure of Metals

The properties of a metal are related to The properties of a metal are related to bonds within the metal.bonds within the metal.


Metallic BondsMetallic Bonds

Metal atoms achieve stable electron Metal atoms achieve stable electron configurations by losing electrons. configurations by losing electrons.

There is a way for metal atoms to gain and There is a way for metal atoms to gain and lose electrons at the same time. lose electrons at the same time.

In a metal, valence electrons are free to In a metal, valence electrons are free to move among the atoms. move among the atoms.

In effect, the metal atoms become cations In effect, the metal atoms become cations surrounded by a pool of shared electrons. surrounded by a pool of shared electrons.


A metallic bond is the attraction between a A metallic bond is the attraction between a metal cation and the shared electrons that metal cation and the shared electrons that surround it.surround it.

The cations in a metal form a lattice that is The cations in a metal form a lattice that is held in place by strong metallic bonds held in place by strong metallic bonds between the cations and the surrounding between the cations and the surrounding valence electrons. valence electrons.


The more valence electrons an atom can The more valence electrons an atom can contribute to the pool, the stronger the contribute to the pool, the stronger the metallic bonds will be. metallic bonds will be.

Transition metals have more valence Transition metals have more valence electrons to contribute and are harder and electrons to contribute and are harder and have higher melting points. have higher melting points.


Typical transition metals have one or two Typical transition metals have one or two valence electrons and are less reactive valence electrons and are less reactive than alkali metals or alkaline earth metals.than alkali metals or alkaline earth metals.Tungsten (“heavy stone” in Swedish) melts Tungsten (“heavy stone” in Swedish) melts at 3410at 3410ooC, the highest melting point of any C, the highest melting point of any metal.metal.Fe, Co, Ni makeup the iron triad. Fe, Co, Ni makeup the iron triad. – Only elements known to create a Only elements known to create a

magnetic field.magnetic field.


Explaining Properties of MetalsExplaining Properties of Metals

The mobility of electrons within a metal The mobility of electrons within a metal lattice explains some of the properties of lattice explains some of the properties of metals. metals.

The ability to conduct electricity and The ability to conduct electricity and malleability are two important properties of malleability are two important properties of metals. metals.


A metal has a built-in supply of charged A metal has a built-in supply of charged particles that can flow from one location to particles that can flow from one location to another in the shared electrons. another in the shared electrons.

The lattice in a metal is flexible compared The lattice in a metal is flexible compared to the rigid lattice in an ionic compound. to the rigid lattice in an ionic compound.


When a metal is struck with a hammer, the When a metal is struck with a hammer, the ions shift positions and the shape of the ions shift positions and the shape of the metal changes. metal changes.

The metal does not shatter because the ions The metal does not shatter because the ions are still held together by the metallic bonds. are still held together by the metallic bonds.

Likewise metals can be drawn into thin wires Likewise metals can be drawn into thin wires without breaking (they are ductile).without breaking (they are ductile).


AlloysAlloys

An alloy is a mixture of two or more An alloy is a mixture of two or more elements, at least one of which is a metal. elements, at least one of which is a metal.

Alloys have the characteristics properties Alloys have the characteristics properties of metalsof metals

– conductorconductor

– malleablemalleable

– ductileductile


Pure Gold – 24 kPure Gold – 24 k

14 k gold – 58% Au and 42% Cu14 k gold – 58% Au and 42% Cu

12 k gold - 50% Au and 50% Cu12 k gold - 50% Au and 50% Cu


Copper AlloysCopper Alloys

The first important alloy was bronze. The first important alloy was bronze. – In its simplest form, bronze contains only In its simplest form, bronze contains only

copper and tin, which are relatively soft. copper and tin, which are relatively soft.

Mixed together in bronze, the metals are much Mixed together in bronze, the metals are much harder and stronger than either metal alone. harder and stronger than either metal alone.

Scientists can design alloys with specific Scientists can design alloys with specific properties by varying the types and amounts properties by varying the types and amounts of elements in the alloy.of elements in the alloy.


Brass is another alloy of copper. Brass is another alloy of copper.

– In its simplest form, brass contains only In its simplest form, brass contains only copper and zinc. copper and zinc.

Brass is shinier than bronze but is likely to Brass is shinier than bronze but is likely to weather more quickly.weather more quickly.


Steel AlloysSteel Alloys

Steel is an alloy of iron that contains Steel is an alloy of iron that contains carbon. carbon.

The carbon atoms form bonds with The carbon atoms form bonds with neighboring iron atoms. neighboring iron atoms.

The bonds make the lattice harder and The bonds make the lattice harder and stronger than a lattice containing iron only. stronger than a lattice containing iron only.

Stainless steel contains chromium and Stainless steel contains chromium and nickel with almost no carbon. nickel with almost no carbon.

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