Chapter 6: Chemical Bonding

11

Chapter 6:Chapter 6:Chemical BondingChemical Bonding

1.1. Use the periodic table to infer the Use the periodic table to infer the number of valence electrons in an number of valence electrons in an atom and draw its electron dot atom and draw its electron dot structure.structure.

2.2. Be able to explain the types of bonds Be able to explain the types of bonds that atoms can form.that atoms can form.

3.3. List the characteristics of the different List the characteristics of the different types of chemical bonds.types of chemical bonds.

4.4. Define the vocabulary words.Define the vocabulary words.5.5. Use electronegativity values to Use electronegativity values to

classify a bondclassify a bond

22

Valence ElectronsValence Electrons Electrons in the highest occupied energy level Electrons in the highest occupied energy level

of an element’s atomsof an element’s atoms For representative elements, the number of For representative elements, the number of

valence electrons is the same as the group valence electrons is the same as the group number of that element (Page 414)number of that element (Page 414)

Shown in electron dot structuresShown in electron dot structures 3 5 3 5 2 1 2 1 6 8 6 8 4 7 4 7 Right, left, top, bottom (1,2,3,4)Right, left, top, bottom (1,2,3,4)Then 12 o’clock and counterclockwise (5,6,7,8)Then 12 o’clock and counterclockwise (5,6,7,8)

Symbol

of the

element

33

Valence Electrons (cont’d)Valence Electrons (cont’d)

Electrons in the highest occupied energy level of an Electrons in the highest occupied energy level of an element’s atomselement’s atoms

Can be figured out using the group numbers in the periodic Can be figured out using the group numbers in the periodic table.table. Ex: The elements of Group 1A (hydrogen, lithium, Ex: The elements of Group 1A (hydrogen, lithium,

sodium, etc.) all have a valence number of sodium, etc.) all have a valence number of 11, which , which means there is 1 electron in the highest occupied energy means there is 1 electron in the highest occupied energy level. The elements of group 7A (fluorine, chlorine, level. The elements of group 7A (fluorine, chlorine, bromine, etc.) have bromine, etc.) have 77 electrons in the outer energy level. electrons in the outer energy level.

The valence numbers also tell us the likely The valence numbers also tell us the likely oxidationoxidation

statestate of that element. More on this later. of that element. More on this later.

44

Oxidation States

The oxidation state of an atom is the charge it has when it gains or loses

electrons to form it’s most stable electron configuration.

Valence Number Oxidation State

(charge on the ion)

1 +1

2 +2

3 +3

5 -3

6 -2

7 -1

}

}

CATIONS

ANIONS

55

The Octet RuleThe Octet Rule Gilbert Lewis used this to explain why atoms form Gilbert Lewis used this to explain why atoms form

certain kinds of ions and molecule. certain kinds of ions and molecule. In forming compounds, atoms tend to achieve the In forming compounds, atoms tend to achieve the

electron configuration of a noble gas (8 valence eelectron configuration of a noble gas (8 valence e --)) Recall that each noble gas (except He) has 8 electronsRecall that each noble gas (except He) has 8 electrons

in its highest energy level and a general electron in its highest energy level and a general electron configuration of nconfiguration of nss22 n npp66

Exceptions: Molecules with an odd number of Exceptions: Molecules with an odd number of electrons, more than an octet (PClelectrons, more than an octet (PCl55), and less than ), and less than an octet (very rare) an octet (very rare)

Example: NOExample: NO22 has seventeen valence electrons has seventeen valence electrons [Nitrogen contributes five and each oxygen [Nitrogen contributes five and each oxygen contributes 6 (2 x 6 =12)]contributes 6 (2 x 6 =12)]

66

The Octet RuleThe Octet Rule An atom’s loss of an electron produces a An atom’s loss of an electron produces a cationcation, or , or positively charged ion. The most common cations are thosepositively charged ion. The most common cations are those

produced by the loss of valence electrons from the metals, produced by the loss of valence electrons from the metals, since most of these atoms have 1-3 valence electrons.since most of these atoms have 1-3 valence electrons.

Let’s look at sodium (a 1A metal) as an example:Let’s look at sodium (a 1A metal) as an example:

Na 1Na 1ss2222ss2222pp6633ss11 NaNa++ 1 1ss2222ss2222pp66-e-

77

Practice ProblemsPractice Problems Write the electron dot structure for each of the Write the electron dot structure for each of the

following:following:

1. Na1. Na

2. Al2. Al

3. N3. N

4. S4. S

5. Kr5. Kr

6. Chloride ion6. Chloride ion

7. Oxide ion7. Oxide ion Refer to pages 414, 417, and 418 for answers. Refer to pages 414, 417, and 418 for answers.

88

Practice ProblemsPractice ProblemsPlease write the Please write the oxidation numbersoxidation numbers of the following: of the following:1)1) NaNa 11) Po11) Po2)2) AlAl 12) Ga12) Ga3)3) FF 13) Cr13) Cr4)4) ClCl 14) N14) N5)5) MgMg6)6) PP7)7) CaCa8)8) SbSb9)9) II10)10) ScSc

99

Common Polyatomic IonsCommon Polyatomic IonsHydroxide:Hydroxide: OHOH-- Permanganate: MnOPermanganate: MnO44

--

Bicarbonate:Bicarbonate: HCOHCO33-- Ammonium: NHAmmonium: NH44

++

Carbonate:Carbonate: COCO332-2- Acetate:Acetate: C C22HH33OO22

--

Sulfate:Sulfate: SOSO442-2- Hydrogen- Hydrogen-

Sulfite:Sulfite: SOSO332-2- Phosphate: HPOPhosphate: HPO44

2-2-

Phosphate:Phosphate: POPO443-3- Dichromate: Dichromate: Cr Cr22OO77

2-2-

Nitrate:Nitrate: NONO33--

Nitrite:Nitrite: NONO22--

Chlorate:Chlorate: ClOClO33--

Cyanide:Cyanide: CNCN--

1010

Chemical BondingChemical Bonding

Chemical energy & potential energy stored Chemical energy & potential energy stored in chemical bondsin chemical bonds

Atoms prefer a low energy conditionAtoms prefer a low energy condition Atoms that are bonded have less energy Atoms that are bonded have less energy

than free atoms- more stable.than free atoms- more stable. To combine atoms: energy is absorbed To combine atoms: energy is absorbed To break a bond: energy is released (AB) To break a bond: energy is released (AB)

1111

Chemical BondsChemical Bonds Created when two nuclei simultaneously Created when two nuclei simultaneously

attract electrons attract electrons When electrons are donated or received, When electrons are donated or received,

creating an ion (anion, cation)creating an ion (anion, cation) In most elements, only valence electrons In most elements, only valence electrons

enter chemical reactionsenter chemical reactions Atoms of everyday substances are held Atoms of everyday substances are held

together by chemical bonds (water, salt together by chemical bonds (water, salt anti-freeze)anti-freeze)

1212

Types of Chemical BondsTypes of Chemical Bonds

1) 1) Ionic BondIonic Bond: : chemical bonding that results fromchemical bonding that results from

the electrical attraction between cations and anions the electrical attraction between cations and anions

where atoms completely give their electron(s) awaywhere atoms completely give their electron(s) away

1313

Types of Chemical BondsTypes of Chemical Bonds

2) 2) Covalent BondCovalent Bond: : chemical bonding that results chemical bonding that results

from the sharing of electron pairs between two atoms.from the sharing of electron pairs between two atoms.

The electrons are “owned” equally by the two atoms.The electrons are “owned” equally by the two atoms.

1414

Relative Forces of Relative Forces of AttractionAttraction

Ability of a nucleus to hold its valence Ability of a nucleus to hold its valence electrons (Group 7A has a greater ability electrons (Group 7A has a greater ability to hold on to its valence electrons than to hold on to its valence electrons than Group 1A)Group 1A)

Ionization energy: energy required to lose Ionization energy: energy required to lose an electron (As atomic number increases an electron (As atomic number increases down a group, the most loosely bound down a group, the most loosely bound electrons are more easily removed, so electrons are more easily removed, so ionization energy decreases. For the ionization energy decreases. For the most part, it increases along each most part, it increases along each period.)period.)

1515

Electron affinity – tendency to gain an Electron affinity – tendency to gain an electron (Energy is released)electron (Energy is released)

Electronegativity – measure of the Electronegativity – measure of the electron attracting power of an atom electron attracting power of an atom when it bonds with another atomwhen it bonds with another atom

* Fluorine (4.0) is the highest * Fluorine (4.0) is the highest * Cesium (0.7) is the lowest – least * Cesium (0.7) is the lowest – least

ability to attract bonding electrons and ability to attract bonding electrons and thus the greatest tendency to lose an thus the greatest tendency to lose an electronelectron

* Noble gases are not assigned * Noble gases are not assigned electronegativities because these electronegativities because these elements do not generally form bonds elements do not generally form bonds (inert)(inert)

1616

The periodic trend of the The periodic trend of the electronegativities is the same as that of electronegativities is the same as that of the ionization energies. Thus, as the the ionization energies. Thus, as the atomic number increases along a period, atomic number increases along a period, the electronegativity increases. As the the electronegativity increases. As the atomic number increases down a group, atomic number increases down a group, the electronegativity decreases. the electronegativity decreases.

In general, metals have a low In general, metals have a low electronegativity and nonmetals have a electronegativity and nonmetals have a high electronegativityhigh electronegativity

1717

Electronegativity and Bond TypesElectronegativity and Bond Types

Covalent BondsCovalent Bonds: bonding between elements with an electro-: bonding between elements with an electro-

negativity difference of negativity difference of 1.7 or less1.7 or less. .

Nonpolar-Covalent BondsNonpolar-Covalent Bonds: covalent bond in which electrons are : covalent bond in which electrons are shared evenly by the bonded atoms with an electronegativity shared evenly by the bonded atoms with an electronegativity difference of difference of 0 – 0.30 – 0.3..

Polar-Covalent BondsPolar-Covalent Bonds: covalent bond in which the bonded atoms : covalent bond in which the bonded atoms have unequal attraction of the shared electrons, and have an have unequal attraction of the shared electrons, and have an electronegativity difference of electronegativity difference of 0.4 – 1.70.4 – 1.7

Ionic BondsIonic Bonds: bonding due to difference in electric charge of two : bonding due to difference in electric charge of two elements due to loss/gain of electrons. Must have an electro- elements due to loss/gain of electrons. Must have an electronegativity of negativity of 1.8 – 4.01.8 – 4.0..

1818


Water is a Water is a polarpolar molecule, because the electrons molecule, because the electronsare not shared evenly by the hydrogen and oxygen.are not shared evenly by the hydrogen and oxygen.

Ionic BondsIonic Bonds: bonds in which electrons are donated from one: bonds in which electrons are donated from oneatom to another and have an electronegativity differenceatom to another and have an electronegativity differenceof of 1.8 or higher1.8 or higher. .

1919


Using the electronegativity values found on page 161 ofUsing the electronegativity values found on page 161 ofyour book, predict the types of bonds the following will form.your book, predict the types of bonds the following will form.

1) O1) O22

2) NaCl2) NaCl

3) N3) N22

4) Knowing that the electronegativity of sulfur is 2.5, what type4) Knowing that the electronegativity of sulfur is 2.5, what typeof bond will sulfur form with:of bond will sulfur form with:

a) hydrogena) hydrogenb) cesiumb) cesiumc) chlorinec) chlorine

2020

ElectronegativityElectronegativityElectronegativity is a measure of how strongly an elementElectronegativity is a measure of how strongly an element

can remove an electron from another element.can remove an electron from another element.

2121

Ionic (Electrovalent) BondsIonic (Electrovalent) Bonds The strongest chemical bondThe strongest chemical bondComplete transfer of electron(s) from one element to anotherComplete transfer of electron(s) from one element to another

Generally formed when metals combine with Generally formed when metals combine with nonmetals (Groups 1-2a w/ 5-7a)nonmetals (Groups 1-2a w/ 5-7a)

Coulombic forces – electrostatic force in which two Coulombic forces – electrostatic force in which two oppositely charged ions are mutually attractedoppositely charged ions are mutually attracted

Usually occurs when the difference in Usually occurs when the difference in electronegativities is 1.8 or greaterelectronegativities is 1.8 or greater

2222

NaCl – Ionic BondNaCl – Ionic Bond Draw Draw

2323


ClNa. :

::.

2424


ClNa. :

::.

2525


ClNa . :

::.

2626


ClNa . :

::.

2727


ClNa: ::

:

2828

Writing Ionic CompoundsWriting Ionic Compounds Beryllium fluoride Beryllium fluoride

Calcium oxideCalcium oxide

Scandium sulfideScandium sulfide

Aluminum chlorideAluminum chloride

2929

Ionic SolidsIonic Solids

Form crystal lattice (orderly, repeating, Form crystal lattice (orderly, repeating, three-dimensional pattern)three-dimensional pattern)

The charges and relative sizes of the The charges and relative sizes of the ions determines the crystal structureions determines the crystal structure

The number of ions of opposite charge The number of ions of opposite charge that surround the ion in a crystal is called that surround the ion in a crystal is called the the coordination numbercoordination number of the ion. of the ion.

3030

Poor conductors of electricity (no free Poor conductors of electricity (no free electrons)electrons)

High melting pointHigh melting point High boiling pointHigh boiling point Brittle and break easily under stressBrittle and break easily under stress Liquid or aqueous: good conductors of Liquid or aqueous: good conductors of

electricity but ionic bond is dissolvedelectricity but ionic bond is dissolved

3131

The Normal Arrangement The Normal Arrangement of an Ionic Crystalof an Ionic Crystal

Opposite charges attractOpposite charges attract

-

-

-

-

-

-

-

- -

-

+

+

+

+

+

+

+

+

+

+

3232

Arrangement when Stress is Arrangement when Stress is AppliedApplied

Adjacent to ions with same charge (repulsion)Adjacent to ions with same charge (repulsion)

+

+

+

-

-

-

-

+

-

+

-

-

+

+

+

+

-

-

+

-

3333

Crystal Lattice is DestroyedCrystal Lattice is Destroyed

Crystal melts, vaporizes, or dissolves in water Crystal melts, vaporizes, or dissolves in water (ions free to move about)(ions free to move about)

Cleavage – splitting along a definite lineCleavage – splitting along a definite line

+

+

+

-

-

-

-

+

-

+

-

-

+

+

+

+

-

-

+

-

3434

Electrons are sharedElectrons are shared One atom does not have enough pull on the One atom does not have enough pull on the

electron to take it completely from the other electron to take it completely from the other atomatom

Occurs when electronegativity difference is 1.7 Occurs when electronegativity difference is 1.7 or lessor less

Covalently Bonded Solids:Covalently Bonded Solids:

1. Softness1. Softness

2. Poor conductor of electricity and heat2. Poor conductor of electricity and heat

3. Low melting point 3. Low melting point

Covalent BondingCovalent Bonding

3535

Lewis StructuresLewis Structures Single covalent bondSingle covalent bond – one shared pair of – one shared pair of

electrons:electrons: HH· + ·H· + ·H H H or H HH H or H H Double covalent bondDouble covalent bond – two shared pairs – two shared pairs

of electronsof electrons

O + OO + O O O or O OO O or O O Triple covalent bondTriple covalent bond – three shared pairs – three shared pairs

of electronsof electrons

N + NN + N N N or N NN N or N N

NoteNote: all of these obey the : all of these obey the octetoctet rule rule

:

: :

::. .. .

::

: : : : : :

: :

: :.. . .

..: : : :: : :

3636

Coordinate covalent bondCoordinate covalent bond – one atom – one atom contributes both bonding electronscontributes both bonding electrons

NHNH33 + H + H++ [NH [NH44]]++

ammonia hydrogen ionammonia hydrogen ion ammonium ion ammonium ion

H H ++ H N H + HH N H + H++ H N H H N H

HH H H The structural formula shows an The structural formula shows an arrowarrow

that points from the atom donating the that points from the atom donating the electrons to the atom receiving them.electrons to the atom receiving them.

Refer to page 444Refer to page 444

: :::

:: :

3737

How to Construct Lewis StructuresHow to Construct Lewis StructuresStep 1Step 1: : Determine the type and # of atoms in moleculeDetermine the type and # of atoms in molecule

CHCH33II

has 1 Carbon, 3 Hydrogens and 1 Iodinehas 1 Carbon, 3 Hydrogens and 1 Iodine

Step 2Step 2: : Write electron dot notation for each type of atomWrite electron dot notation for each type of atom

CC HH· I· I

Step 3Step 3: Determine the total # of electrons available in : Determine the total # of electrons available in

the atoms to be combined.the atoms to be combined.

CC 1 x 4e1 x 4e-- = 4e = 4e--

II 1 x 7e1 x 7e-- = 7e = 7e--

HH 3 x 1e3 x 1e-- = 3e = 3e--

14 e14 e--

. ..

. .. ..

. ..

3838

How to Construct Lewis StructuresHow to Construct Lewis StructuresStep 4Step 4: : Arrange the atoms to form a skeleton structureArrange the atoms to form a skeleton structure

for the molecule. Then connect the atoms byfor the molecule. Then connect the atoms by

electron-pair bonds. electron-pair bonds.

H C IH C I

Step 5Step 5: Add unshared pairs of electrons to each non-: Add unshared pairs of electrons to each non-

metal atom so that each is surrounded by 8.metal atom so that each is surrounded by 8.

HH C IC I

. ...

. . . .

H

H

. ...

.. .H

H

. . ..

. ..

3939

Electron Dot Practice: CompoundsElectron Dot Practice: Compounds

1)1) HH22OO 5) CCl5) CCl22HH22

2)2) HH22OO22 6) NH6) NH33

3)3) HCNHCN 7) N7) N22

4)4) AlFAlF33 8) CO8) CO22

4040

A single water molecule is a good example of covalent bonding A single water molecule is a good example of covalent bonding between atoms. The hydrogen atoms “share” their electrons with between atoms. The hydrogen atoms “share” their electrons with the larger oxygen atom so that oxygen now has a full outer level the larger oxygen atom so that oxygen now has a full outer level with 8 electrons and each hydrogen has a full outer level with 2 with 8 electrons and each hydrogen has a full outer level with 2 electrons. Oxygen has a higher electronegativity than hydrogen, electrons. Oxygen has a higher electronegativity than hydrogen, so there is actually an uneven sharing of electrons, resulting in a so there is actually an uneven sharing of electrons, resulting in a polar molecule. More on this later. polar molecule. More on this later.

8p+

8n0

e-

e- e-

e- e-

e-

e-e-

e-e-

1p+ 1p+

shared electrons shared electrons

4141

Bond dissociation energyBond dissociation energy: total energy required to : total energy required to break the bond between two covalently bonded atoms break the bond between two covalently bonded atoms (remember that energy is measured in (remember that energy is measured in joulesjoules or or kilojouleskilojoules))

HH–H + 435 kJ–H + 435 kJ H + HH + H

Resonance StructuresResonance Structures: refers to bonding in molecules: refers to bonding in molecules

or ions that cannot be correctly represented by a or ions that cannot be correctly represented by a

single Lewis structure.single Lewis structure.

. .

4242

Bond Length vs. Bond Bond Length vs. Bond EnergyEnergyThere is a correlation between bond There is a correlation between bond lengthlength and the amount and the amount

of potential energy stored in that bond. For example:of potential energy stored in that bond. For example:

Bond Bond Length (pm) Bond energy (Kj/mol) Bond Bond Length (pm) Bond energy (Kj/mol)

C CC C 154154 346346

CC CC 134134 612612

CC CC 120120 835835

CC NN 147147 305305

CC NN 132132 615615

CC NN 116116 887887

NN NN 145145 163163

NN NN 125125 418418

NN NN 110110 945945

4343

Molecular orbitals – when two atoms combine and their Molecular orbitals – when two atoms combine and their atomic orbitals overlapatomic orbitals overlap

Sigma bond - molecular orbital that is symmetrical Sigma bond - molecular orbital that is symmetrical

along the axis connecting two atomic nucleialong the axis connecting two atomic nuclei

In both of these examples, the In both of these examples, the pp orbitals are overlapping orbitals are overlapping and sharing electrons.and sharing electrons.

4444

pi bond – weaker than sigma bond; usually pi bond – weaker than sigma bond; usually sausage-shaped regions above and below the sausage-shaped regions above and below the bond axis (Page 445)bond axis (Page 445)

4545

Examples of Sigma and Pi bondsExamples of Sigma and Pi bonds

H3C – CH3

H2C = CH2

H3C – CH3

HC CH–––

4646

VSEPR Theory (page 200)VSEPR Theory (page 200)VSEPR TheoryVSEPR Theory ( (VValence alence SShell hell EElectron-lectron-PPair air RRepulsion theory):epulsion theory):

states that repulsion between the sets of valence-level electrons states that repulsion between the sets of valence-level electrons surrounding an atom causes these sets to be oriented as far surrounding an atom causes these sets to be oriented as far

away from each other as possible, thus determining the shape away from each other as possible, thus determining the shape of molecules.of molecules.

4747

VSEPR TheoryVSEPR TheorySo then why is HSo then why is H22O bent, but BeFO bent, but BeF22 is linear? is linear?

The answer is the The answer is the free electron pairsfree electron pairs. Oxygen has 2 pairs, . Oxygen has 2 pairs, beryllium has none. beryllium has none.

HH22OO BeFBeF22

Be. .O::

..

1

2

4848

VSEPR ShapesVSEPR Shapes

LinearLinear

Trigonal-PlanerTrigonal-Planer

Bent/AngularBent/Angular

TetrahedralTetrahedral

Trigonal-PyramidalTrigonal-Pyramidal

Trigonal-BipyramidalTrigonal-Bipyramidal

OctahedralOctahedral (#s 3, 5 and 7 are (#s 3, 5 and 7 are coordinate covalent bonds!)coordinate covalent bonds!)

4949

VSEPR TheoryVSEPR TheoryThese free electron pairs These free electron pairs repelrepel each other because they have a each other because they have a

negative charge, and so they force those atoms that arenegative charge, and so they force those atoms that are

covalently bonded to be pushed as far away as possible. covalently bonded to be pushed as far away as possible. . . .

.

5050

Hybridization – several atomic orbitals Hybridization – several atomic orbitals mix to form the same total number of mix to form the same total number of equivalent hybrid orbitals (CHequivalent hybrid orbitals (CH4 4 – Page – Page

457457 ) )

*Note: An sp*Note: An sp33 orbital is an example of a orbital is an example of a hybrid.hybrid.

5151

Types of Covalent Types of Covalent BondingBonding

1. Nonpolar – when atoms have the same or1. Nonpolar – when atoms have the same or

similar electronegativity; when the atoms insimilar electronegativity; when the atoms in

the bond pull equally and the bonding the bond pull equally and the bonding

electrons are shared equally.electrons are shared equally.

(Generally a difference of 0.0- 0.4)(Generally a difference of 0.0- 0.4)

* Examples: Diatomic elements* Examples: Diatomic elements

(H(H2 2 , N, N2 2 , O, O22 , F , F22 , Cl , Cl22 , I , I22 , Br , Br22) )

* Nonpolar Covalent: * Nonpolar Covalent:

Bonded Hydrogen AtomsBonded Hydrogen Atoms

5252

2. Polar – unequal sharing of electrons2. Polar – unequal sharing of electrons

* Pairing of atoms when one has a stronger * Pairing of atoms when one has a stronger

attraction for the electronsattraction for the electrons

* Most compounds are polar covalent* Most compounds are polar covalent

Examples: HExamples: H22O , NHO , NH33 , HF , HCl , HF , HCl

* Polar covalent also called dipoles* Polar covalent also called dipoles

* Creates partial charges* Creates partial charges

Partially +Partially +

Partially -Partially -

Example: HCl (0.9 difference of the electro-Example: HCl (0.9 difference of the electro-

negativities) H (2.1) Cl (3.0)negativities) H (2.1) Cl (3.0)

Electronegativity difference is less than 1.7 Electronegativity difference is less than 1.7

5353

Example: Example: waterwater..An uneven distribution of the electrons results because An uneven distribution of the electrons results because

the oxygen has a higher electron affinity than the the oxygen has a higher electron affinity than the hydrogens. Thus, you have a negative and positive end hydrogens. Thus, you have a negative and positive end of the molecule: polarity. Because this molecule has of the molecule: polarity. Because this molecule has 22

poles, it is called a poles, it is called a dipoledipole molecule. molecule.

8p+

8n0

e-

e- e-

e- e-

e-

e-e-

e-e-

1p+ 1p+

Oxygen

Hydrogens

δδ - -

δδ + +

δδ = delta or = delta or overall overall

5454

Attractions Between MoleculesAttractions Between MoleculesMolecules are often attracted to each other by a variety of Molecules are often attracted to each other by a variety of

forces. The forces. The intermolecularintermolecular attractions are weaker than either attractions are weaker than either an ionic or covalent bond. These attractions are responsible an ionic or covalent bond. These attractions are responsible

for determining whether a molecular compound is a gas, liquid,for determining whether a molecular compound is a gas, liquid, or solid at a given temperature. Here is a list of these various or solid at a given temperature. Here is a list of these various

attractions:attractions:1. 1. van der Waals forcesvan der Waals forces: weakest type of intermolecular : weakest type of intermolecular attractions.attractions.

Dispersion (London) forcesDispersion (London) forces: weakest of all molecular : weakest of all molecular interactions, caused by the motion of electrons. interactions, caused by the motion of electrons. Increases as the # of electrons increases. Increases as the # of electrons increases.

Ex: Cl & F are gases at STP; Br is liquid at STP; Ex: Cl & F are gases at STP; Br is liquid at STP; I is solid at STP.I is solid at STP.

5555

2. 2. Dipole InteractionsDipole Interactions: attraction of polar molecules to one : attraction of polar molecules to one another. Remember that polar molecules are like magnets; they another. Remember that polar molecules are like magnets; they have a positive and negative end. have a positive and negative end.

A glucose molecule A glucose molecule

in water has many dipolein water has many dipole

interactions since bothinteractions since both

water and glucose arewater and glucose are

polar. The positive polespolar. The positive poles

of the water molecule areof the water molecule are

attracted to the negativeattracted to the negative

poles on the glucose andpoles on the glucose and

vice versa.vice versa.

5656

3. 3. Hydrogen BondsHydrogen Bonds: attractive forces in which a hydrogen : attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also covalently bonded to a very electronegative atom is also weakly bonded to an unshaired pair of electrons on another weakly bonded to an unshaired pair of electrons on another electronegative. Hydrogen bonding always involves electronegative. Hydrogen bonding always involves hydrogen. Hence the name. Duh.hydrogen. Hence the name. Duh.

The hydrogen bonding between The hydrogen bonding between

water molecules dictates many water molecules dictates many of of

the properties of water. It alsothe properties of water. It also

explains why water is a liquid explains why water is a liquid

rather than a gas at room rather than a gas at room

temperature.temperature.

5757

Network SolidsNetwork Solids MacromoleculesMacromolecules Covalent network of atoms bondedCovalent network of atoms bonded Absence of molecules throughout the solidAbsence of molecules throughout the solid PropertiesProperties

1. Hardness1. Hardness

2. Poor conductor of electricity (electrical 2. Poor conductor of electricity (electrical

insulation) insulation)

3. Poor conductor of heat3. Poor conductor of heat

4. High melting point4. High melting point

5858

Examples: diamond graphite (carbon)Examples: diamond graphite (carbon) Does not melt - vaporizes to a gas at 3500 Does not melt - vaporizes to a gas at 3500 °C°C

Carbon atomCarbon atom

Covalent bondCovalent bond

Boron nitride (BN), asbestos, silicone carbide Boron nitride (BN), asbestos, silicone carbide (SiC, grindstones), silicone dioxide (SiO(SiC, grindstones), silicone dioxide (SiO22 , , quartz) quartz)

5959

Metallic BondsMetallic Bonds Most metallic elements, except liquid Most metallic elements, except liquid

mercury, are solids at room temperature mercury, are solids at room temperature and exhibit a crystal structure (zinc)and exhibit a crystal structure (zinc)

Arrangement of stationary positive metal Arrangement of stationary positive metal ions surrounded by a “sea of mobile ions surrounded by a “sea of mobile electrons””electrons””

- - - -- - - - - - - -- - - - - - - -- - - - - - - - - - - -

+

+

+ +

+

+

+

+

+

6060

Properties:Properties:

1. Malleability – ability to be hammered 1. Malleability – ability to be hammered

into different shapesinto different shapes

2. Ductility – ability to be drawn into wire2. Ductility – ability to be drawn into wire

3. Conductor of heat3. Conductor of heat

4. Conductor of electricity4. Conductor of electricity

5. Luster – shine5. Luster – shine

6. Tenacity – structural strength 6. Tenacity – structural strength

(resistance to being pulled apart) (resistance to being pulled apart)

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AlloysAlloys Mixtures composed of two or more elements, at least Mixtures composed of two or more elements, at least

one of which is a metalone of which is a metal Properties usually superior to those of the component Properties usually superior to those of the component

elementselements Sterling silver – silver and copperSterling silver – silver and copper Bronze – copper and tinBronze – copper and tin Steel – iron, carbon, boron, chromium, manganese, Steel – iron, carbon, boron, chromium, manganese,

molybdenum, nickel, tungsten, vanadium (Interstitial molybdenum, nickel, tungsten, vanadium (Interstitial alloy)alloy)

Interstitial alloy – smaller atoms fit into spaces between Interstitial alloy – smaller atoms fit into spaces between larger atomslarger atoms

Substitutional alloy – atoms of the components are Substitutional alloy – atoms of the components are about the same size (They can replace each other in about the same size (They can replace each other in the structure.)the structure.)

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Summary : Types of Bonds Summary : Types of Bonds 1. Ionic – complete transfer of electrons1. Ionic – complete transfer of electrons2.2. Covalent – share electronsCovalent – share electrons A. Nonpolar : same or similar electronegativity A. Nonpolar : same or similar electronegativity B. Polar – unequal sharingB. Polar – unequal sharing Electronegativity Difference:Electronegativity Difference: CC << 2.0 2.0 ≤ ≤ II (Know exceptions) (Know exceptions) *Know table on page 465*Know table on page 4653.3. Network solids – covalent network of atoms Network solids – covalent network of atoms

(absence of molecules)(absence of molecules)4.4. Metallic – positive ions around a “sea of mobile Metallic – positive ions around a “sea of mobile

electrons” electrons”

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Electronegativity Electronegativity Differences and Bond TypesDifferences and Bond Types

0.0-0.3 Nonpolar covalent0.0-0.3 Nonpolar covalent 0.4-1.0 Moderately polar covalent0.4-1.0 Moderately polar covalent 1.0-1.8 Very polar covalent1.0-1.8 Very polar covalent 1.8 or greater Ionic1.8 or greater Ionic

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General Trends of the General Trends of the Representative Elements Representative Elements

Group 1A - lose one electronGroup 1A - lose one electron Group 2A - lose two electronsGroup 2A - lose two electrons Group 3A - lose three electrons Group 3A - lose three electrons Group 4A - share, lose or gain 4 e-Group 4A - share, lose or gain 4 e- Group 5A - share, gain three electronsGroup 5A - share, gain three electrons Group 6A - share, gain two electronsGroup 6A - share, gain two electrons Group 7A - gain one electronGroup 7A - gain one electron Group 8 - do not react, noble gases Group 8 - do not react, noble gases

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Think!Think! Why is it possible to bend metals but not Why is it possible to bend metals but not

ionic crystals?ionic crystals? In an ionic compound, ions of like charge In an ionic compound, ions of like charge

do not have mobile electrons as do not have mobile electrons as insulation. When forced into contact by insulation. When forced into contact by physical stress, the ions of like charge physical stress, the ions of like charge repel, causing the crystal to shatter.repel, causing the crystal to shatter.

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Attractions Attractions between Moleculesbetween MoleculesName and describe the weak Name and describe the weak attractive forces that hold groups of attractive forces that hold groups of molecules together.molecules together.

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Van der Waals ForcesVan der Waals Forces Weaker than either an ionic or covalent Weaker than either an ionic or covalent

bondbond Responsible for determining whether a Responsible for determining whether a

molecular compound is a gas, liquid, or molecular compound is a gas, liquid, or solid at a given temperaturesolid at a given temperature

Two types: dispersion forces and dipole Two types: dispersion forces and dipole interactionsinteractions

Dispersion – caused by motion of Dispersion – caused by motion of electrons; dispersion generally increases electrons; dispersion generally increases as the number of electrons increasesas the number of electrons increases

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Example of dispersion forces: (Refer to Example of dispersion forces: (Refer to Group 7A) F and Cl are gases at STP; Br Group 7A) F and Cl are gases at STP; Br is a liquid at STP, and I is a solid at STPis a liquid at STP, and I is a solid at STP

Dipole interactions – electrostatic Dipole interactions – electrostatic attractions between oppositely charged attractions between oppositely charged regions (Example: water) regions (Example: water)

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Hydrogen BondsHydrogen Bonds

Strongest of the intermolecular forcesStrongest of the intermolecular forces Important in determining the properties of Important in determining the properties of

water and biological molecules such as water and biological molecules such as proteinsproteins

Has only about 5% of the strength of an Has only about 5% of the strength of an average covalent bondaverage covalent bond

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Chapter 6: Chemical Bonding