CHEMICAL BONDSCHEMICAL BONDS

An Element’s Search for An Element’s Search for HappinessHappiness

(chemical stability)(chemical stability)

CHEMICAL BONDSCHEMICAL BONDS

The forces that hold atoms together…The forces that hold atoms together…often driven by the Octet Rule and often driven by the Octet Rule and

stability.stability.

(Mutual electrical attraction between (Mutual electrical attraction between nuclei and valence electrons of nuclei and valence electrons of

different atoms that binds them.)different atoms that binds them.)

Chemical BondsChemical Bonds

The negatively charged The negatively charged electrons determine how two electrons determine how two or more atoms will interact or more atoms will interact when they are brought near when they are brought near each other.  In a sense, the each other.  In a sense, the

atoms fight over the available atoms fight over the available electronselectrons

Octet RuleAtoms tend to gain, lose, or share electrons in order to acquire a full

set of valence electrons.

8 (most of the time) 2 (1st energy level)or

Happy dogs!

IONIC BONDSIONIC BONDS

One big greedy thief dog!One big greedy thief dog!Ionic bonding can be best imagined as one Ionic bonding can be best imagined as one

big greedy dog stealing the other dog's big greedy dog stealing the other dog's bone. bone. 

IONIC BONDSIONIC BONDSChemical bonding that results from transfer of Chemical bonding that results from transfer of

electrons and electrical attraction between cations electrons and electrical attraction between cations and anions.and anions.

Form between metals Form between metals (on the left side of the (on the left side of the Periodic Table)Periodic Table) and non-metals and non-metals (on the right side of (on the right side of Periodic Table)Periodic Table)

Metal loses electron(s) and becomes positively Metal loses electron(s) and becomes positively charged…a cation.charged…a cation.

Non-metal gains electron(s) and becomes Non-metal gains electron(s) and becomes negatively charged…an anion.negatively charged…an anion.

The oppositely charged ions are held together The oppositely charged ions are held together because they are strongly attracted to each other.because they are strongly attracted to each other.

Determine difference in electronegativity Determine difference in electronegativity – See page 429See page 429– Difference of greater than 1.7 is often considered ionicDifference of greater than 1.7 is often considered ionic– Ionic character greater than 50%Ionic character greater than 50%

IONIC BOND?IONIC BOND?

Cs and F? Cs and F?

Page 429 electronegativity chartPage 429 electronegativity chart

F en = 4.0F en = 4.0

Cs en = 0.7Cs en = 0.7

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

3.3 is the electronegativity difference3.3 is the electronegativity difference A bond between Cs and F is ionic, greater than 1.7A bond between Cs and F is ionic, greater than 1.7

IONIC COMPOUNDSIONIC COMPOUNDS Expressed as “formula units” rather than Expressed as “formula units” rather than

molecules because they form networks of ions molecules because they form networks of ions attracted to each other…not independent neutral attracted to each other…not independent neutral units.units.

Characteristics:Characteristics:– Crystalline structureCrystalline structure– High melting pointsHigh melting points– BrittleBrittle– Dissolve in waterDissolve in water– This separates the ions by breaking the ionic This separates the ions by breaking the ionic

bonds…separated ions move freely making solution of bonds…separated ions move freely making solution of ionic compounds good conductors of electricity.ionic compounds good conductors of electricity.

– Also conductive when melted.Also conductive when melted.

Formula unit is NaCl, 1 sodium and 1 Formula unit is NaCl, 1 sodium and 1 choride, the simplest ratiochoride, the simplest ratioIonic compounds form orderly arrangements of the ions , Ionic compounds form orderly arrangements of the ions , called crystal lattices.called crystal lattices.

COVALENT BONDSBonds formed when electrons are

shared

Covalent bonds form between non-metals(on the right side of the Periodic Table)

The electrons are shared by the atoms. Electrons may be shared equally or

unequally. Molecules are formed because atoms

sharing electrons must be near each other

COVALENT BONDS

Enormous variety of size, shape, physical, Enormous variety of size, shape, physical, and chemical properties.and chemical properties. often lower melting point, often lower melting point, not necessarily crystalline not necessarily crystalline do not conduct electricity, do not conduct electricity, may or may not dissolve in watermay or may not dissolve in water

COVALENT BONDSThe dogs share the bones.

There are two types of sharing:

UNEQUAL EQUAL

POLAR COVALENT BONDSPOLAR COVALENT BONDS

In a covalent bond, the electrons are shared In a covalent bond, the electrons are shared between atoms to fulfill the Octet Rule for both.between atoms to fulfill the Octet Rule for both.

In a polar covalent bond, the electrons are In a polar covalent bond, the electrons are shared unequally. They are attracted more to the more shared unequally. They are attracted more to the more electronegative element.electronegative element.

The electrons spend more time near the more The electrons spend more time near the more electronegative element, making it seem more electronegative element, making it seem more negative and the other end of the molecule seem more negative and the other end of the molecule seem more positive…or “polar”positive…or “polar”

Determine difference in electronegativity Determine difference in electronegativity – See page 429See page 429– Difference of .3-1.7 is often considered polar covalent…but different Difference of .3-1.7 is often considered polar covalent…but different

sources give different rangessources give different ranges– Ionic character 5-50%Ionic character 5-50%

POLAR COVALENT BONDSPOLAR COVALENT BONDS

Unevenly matched dogs that are Unevenly matched dogs that are willing to share.willing to share.

These bonds can be thought of as two or These bonds can be thought of as two or more dogs that have different desire for more dogs that have different desire for

bones. They share unequally.bones. They share unequally.

POLAR COVALENT BOND?POLAR COVALENT BOND?

Unequal sharing of electronsUnequal sharing of electrons

Partial negativechargePartial

positive charge

POLAR COVALENT BOND?POLAR COVALENT BOND?

H and S?H and S?

Page 429Page 429

S en = 2.5S en = 2.5

H en = 2.1H en = 2.1

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

0.4 is the electronegativity 0.4 is the electronegativity differencedifference

A bond between H and S is polar covalent, .3-1.7A bond between H and S is polar covalent, .3-1.7

Polar molecules and polar Polar molecules and polar bondsbonds

Partial positive charge towards less electronegative element

Partial negative charge towards element with greater electronegativity.

Two sides to the molecules/bonds

S

Polar bonds lead to polar Polar bonds lead to polar moleculesmolecules

Polamolecules

Calm, quiet, humble on the sideline Fearless, crazed, maniacal on the

field

Two sides to Troy Polamalu

Polar molecules and polar Polar molecules and polar bondsbonds

Partial positive charge towards less electronegative element

Partial negative charge towards element with greater electronegativity.

Two sides to the molecules/bonds

S

NON-POLAR COVALENT NON-POLAR COVALENT BONDSBONDS

In a covalent bond, the electrons are shared In a covalent bond, the electrons are shared between atoms to fulfill the Octet Rule for both.between atoms to fulfill the Octet Rule for both.

In a non-polar covalent bond, the electrons In a non-polar covalent bond, the electrons are shared equally.are shared equally.

The charge is evenly distributed between The charge is evenly distributed between both atoms.  The molecule is non-polar meaning both atoms.  The molecule is non-polar meaning one side does not have more charge than the one side does not have more charge than the other. other.

Determine difference in electronegativity Determine difference in electronegativity – See page 429See page 429– Difference of less than .3 is often considered nonpolar covalent…again Difference of less than .3 is often considered nonpolar covalent…again

some sources give different rangesome sources give different range– Ionic character less than 5 %Ionic character less than 5 %

NON-POLAR COVALENT NON-POLAR COVALENT BONDSBONDS

Covalent Bonds: Dogs of equal strength Covalent Bonds: Dogs of equal strength share equally.share equally.

Covalent bonds can be thought of as two or Covalent bonds can be thought of as two or more dogs with equal attraction to the bones. more dogs with equal attraction to the bones. 

They share equally.They share equally.

NON-POLAR COVALENT NON-POLAR COVALENT BOND?BOND?

Cl and Br?Cl and Br?

Page 429 for enPage 429 for en

Cl en = 3.0Cl en = 3.0

Br en = 2.8Br en = 2.8

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

0.2 is the electronegativity difference0.2 is the electronegativity difference A bond between Cl and Br is non=polar covalent, A bond between Cl and Br is non=polar covalent,

less than 0.3less than 0.3

NON-POLAR COVALENT NON-POLAR COVALENT BOND?BOND?

Equal sharing of electronsEqual sharing of electrons

Equaldistribution of charge

Equaldistribution of charge

Diatomic ElementsDiatomic ElementsThey pair up!They pair up!

BrBr22

II22

NN22

ClCl22 HH22

OO22

FF22

The diabolical DIATOMIC BrINClHOF TWINS!

METALLIC BONDsMETALLIC BONDs

Electrons are “delocalized”Electrons are “delocalized” Electrons move freely around and Electrons move freely around and

between atoms in the network of between atoms in the network of empty orbitals. The electrons move empty orbitals. The electrons move through the substance with little through the substance with little restriction.  The model is often restriction.  The model is often described as the "kernels of atoms in described as the "kernels of atoms in a sea of electrons.”a sea of electrons.”

METALLIC BONDSMETALLIC BONDS

The free movement of electrons The free movement of electrons explains the properties of metals…explains the properties of metals… Conductivity: free movement of Conductivity: free movement of

electrons electrons Malleability & ductility: bonding is the Malleability & ductility: bonding is the

same in all directionssame in all directions Luster: energy released as electrons Luster: energy released as electrons

move easily between orbitalsmove easily between orbitals

METALLIC BONDSMETALLIC BONDS

Mellow dogs with plenty of bones to go Mellow dogs with plenty of bones to go around. They don’t have to worry about around. They don’t have to worry about

sharing!sharing!

We will look more closely at the different types of bonds

to understand how millions of different compounds form

from only about 100 different elements!

Lewis Dot of Ionic Lewis Dot of Ionic Compounds (electrons Compounds (electrons

taken, not shared)taken, not shared) Write the dot structures of the neutral Write the dot structures of the neutral

atomsatoms Write the ions created by the loss or Write the ions created by the loss or

gain of electrons, in brackets. The gain of electrons, in brackets. The metals have no dots. The non-metals metals have no dots. The non-metals have a full outer shell. have a full outer shell.

Show the ion charges as superscripts.Show the ion charges as superscripts. Show the ratio of ions needed to create Show the ratio of ions needed to create

a net charge of zero as a subscript.a net charge of zero as a subscript.

Criss-Cross Method to Criss-Cross Method to Determine Ratio of IonsDetermine Ratio of Ions

Write the ion symbols and charges Write the ion symbols and charges (superscripts). (superscripts). Get this info from periodic Get this info from periodic table for elements, polyatomic ion list for table for elements, polyatomic ion list for polyatomic ions.polyatomic ions.

Criss-cross the charge (numbers Criss-cross the charge (numbers only) to subscripts. only) to subscripts. This shows the ratio of This shows the ratio of ions required for a net charge of zero.ions required for a net charge of zero.

Simplify.Simplify. Mg Mg2+2+ N N3-3-

MgMg33NN22

Charges of ions from PTCharges of ions from PTgrou

p1 2 13 14 15 16 17 18

ve 1 2 3 4 5 6 7 2 or 8

charge

1+ 2+ 3+ 4+/- 3- 2- 1- 0

Why does it work?Why does it work?

The goal is a net charge of 0. The The goal is a net charge of 0. The charges, or oxidation numbers, must charges, or oxidation numbers, must

add up to zero.add up to zero.

MgMg33NN22

3 x 23 x 2++ = 6= 6++

2 x 32 x 3--= 6= 6--

0 net charge0 net charge

Covalent bonds Covalent bonds usually usually follow the octet follow the octet rulerule

Put all of the valence electrons in a Put all of the valence electrons in a pot and distribute them between the pot and distribute them between the atoms so each atom has a full octet atoms so each atom has a full octet by sharing up to 3 pairs of electrons.by sharing up to 3 pairs of electrons.

: single bond

:: double bond

:: triple bond

Lewis Dot Structures of Lewis Dot Structures of Covalent Bonds(shared Covalent Bonds(shared

electrons)electrons) Lewis dot structures show atoms near each Lewis dot structures show atoms near each

other sharing pairs of electrons to create other sharing pairs of electrons to create bonds and satisfy octet rule for both atoms.bonds and satisfy octet rule for both atoms.

They may share up to 3 pairs of electronsThey may share up to 3 pairs of electrons– 1 SHARED PAIR :SINGLE BOND 1 SHARED PAIR :SINGLE BOND – 2 SHARED PAIRS ::DOUBLE BOND2 SHARED PAIRS ::DOUBLE BOND– 3SHARED PAIRS :::TRIPLE BOND3SHARED PAIRS :::TRIPLE BOND

It does not matter which atom the electrons It does not matter which atom the electrons come from because they are shared.come from because they are shared.

Lewis Dot Structures of Lewis Dot Structures of Covalent CompoundsCovalent Compounds

Molecules are formedMolecules are formed Atoms sharing electrons stay near Atoms sharing electrons stay near

each othereach other Shared electrons that are involved in Shared electrons that are involved in

bonds are shown using pairs of dots :bonds are shown using pairs of dots : OR pairs of dots in a bond may be OR pairs of dots in a bond may be

replaced by single lines - a line for replaced by single lines - a line for each shared pair of electronseach shared pair of electrons

NomenclatureNomenclature A fancy word for naming thingsA fancy word for naming things

– Looking at a formula and giving the Looking at a formula and giving the compound a namecompound a name

– Looking at a name and writing the formulaLooking at a name and writing the formula USE THE FLOW CHART FOR THE USE THE FLOW CHART FOR THE

HOMEWORK EVERY TIMEHOMEWORK EVERY TIME– By the time you have finished the packet, By the time you have finished the packet,

you will understand the system IF you THINK you will understand the system IF you THINK about what you are doing and use the flow about what you are doing and use the flow chartchart

Binary compoundsBinary compounds

2 elements2 elements Where are they on PT?Where are they on PT?

– Metal and non-metal: ionicMetal and non-metal: ionic Name the metalName the metal Name the non-metal with an –ide endingName the non-metal with an –ide ending Include a Roman numeral to show the Include a Roman numeral to show the

charge of the metal if it is a transition metal charge of the metal if it is a transition metal (exceptions,Ag, Cd, Zn do NOT need Roman (exceptions,Ag, Cd, Zn do NOT need Roman numeral and Sn, Sb, and Pb DO need a numeral and Sn, Sb, and Pb DO need a Roman numeralRoman numeral

Binary compoundsBinary compounds

2 elements2 elements Where are they on PT?Where are they on PT?

– Non-metal and non-metal: CovalentNon-metal and non-metal: Covalent Name the first element using prefix only if Name the first element using prefix only if

there is more than 1there is more than 1 Name the second element with a prefix and an Name the second element with a prefix and an

––ide endingide ending

Mono,di,tri,tetra,penta,hexa,hepta,octa,nona,deMono,di,tri,tetra,penta,hexa,hepta,octa,nona,decaca

Tertiary compoundsTertiary compounds

3 or more elements3 or more elements Involve polyatomic ions: groups of atoms bonded Involve polyatomic ions: groups of atoms bonded

covalently and moving together as a charged group, covalently and moving together as a charged group, an ion made up of several covalently bonded atomsan ion made up of several covalently bonded atoms

See your listSee your list They have specific formulas, names, and charges They have specific formulas, names, and charges

which must be memorizedwhich must be memorized EXAMPLESEXAMPLES

– NH41+ ammoniumammonium

– OH1- hydroxidehydroxide

– SO42- sulfatesulfate

Writing formulas…Writing formulas…reverse the processreverse the process

Prefixes?Prefixes?– The prefixes tell you the number of each The prefixes tell you the number of each

elementelement– Elements written in orderElements written in order– No Criss-crossNo Criss-cross

No prefixes…ionicNo prefixes…ionic

What is the ending?What is the ending?– -ide? Usually binary -ide? Usually binary (exceptions ammonium and (exceptions ammonium and

hydroxide)hydroxide)

Write the symbol and charge of each Write the symbol and charge of each element or ionelement or ion

– Charges of transition elements are the Roman Charges of transition elements are the Roman numeralsnumerals

– Charges of others are from PTCharges of others are from PT

Criss-cross charge numbers to determine Criss-cross charge numbers to determine subscripts which will yield net charge of subscripts which will yield net charge of zero. (Reduce, assume “ones”)zero. (Reduce, assume “ones”)

No prefixes…ionicNo prefixes…ionic

What is the ending?What is the ending?– -ite or –ate-ite or –ate– PolyatomicPolyatomic– Find the polyatomic ions and elementsFind the polyatomic ions and elements– Write symbols and charges of eachWrite symbols and charges of each– Criss-crossCriss-cross

AcidsAcids If hydrogen is the cation, the substance is If hydrogen is the cation, the substance is

an acidan acid If the anion ends in –ideIf the anion ends in –ide

– Hydro+name of anion with –ic ending+ acidHydro+name of anion with –ic ending+ acid If the anion ends in –ateIf the anion ends in –ate

– Name anion with –ic ending+ acidName anion with –ic ending+ acid If the anion ends in –iteIf the anion ends in –ite

– Name the anion with –ous ending+ acidName the anion with –ous ending+ acid

– Reverse rules for formula writingReverse rules for formula writing

HydratesHydrates

Some compounds absorb water in a Some compounds absorb water in a specific ration into the crystal structurespecific ration into the crystal structure

Name the compound following the rulesName the compound following the rules Add a big dotAdd a big dot Use a prefix in front of the word hydrate Use a prefix in front of the word hydrate

to show how many water moleculesto show how many water molecules

Reverse rules for formula writingReverse rules for formula writing