chapter 6: bonding or a scientific drama. quick review what is a molecule? two or more atoms...

Chapter 6: Bonding

orA Scientific Drama

Chapter 6: Bonding

orA Scientific Drama

Quick ReviewQuick Review

What is a molecule? Two or more atoms joined by

bonds What is a compound?

A molecule made up of more than one kind of atom

Binary compounds: 2 atoms Ternary compounds: 3

atoms

But what is a bond?

What is a molecule? Two or more atoms joined by

bonds What is a compound?

A molecule made up of more than one kind of atom

Binary compounds: 2 atoms Ternary compounds: 3

atoms

But what is a bond?A ‘diatomic’ chlorine molecule

Buckminsterfullerene

BondsBonds

Bonds hold molecules together Different types of bonds

give different properties Bond: force of attraction

between protons (nucleus) of one atom and electrons of another

Takes two electrons &

two nuclei

Bonds hold molecules together Different types of bonds

give different properties Bond: force of attraction

between protons (nucleus) of one atom and electrons of another

Takes two electrons &

two nuclei

BondFormatio

n

BondFormatio

n Electron orbitals overlap and hold two electrons in place

Bonds form when attraction > repulsion

Electron orbitals overlap and hold two electrons in place

Bonds form when attraction > repulsion

Making BondsMaking Bonds

Bond formation is SPONTANEOUS : System goes from high to low

energy, by releasing energy Creates stability

Bond formation is SPONTANEOUS : System goes from high to low

energy, by releasing energy Creates stability

Breaking BondsBreaking Bonds

Bond breaking is

NOT SPONTANEOUS System goes from low to high

energy, needs to get that energy from somewhere else

Bond breaking is

NOT SPONTANEOUS System goes from low to high

energy, needs to get that energy from somewhere else

Bonds and Energy LevelsBonds and Energy Levels

Kinetic and potential energies both decrease when bonds are formed

Kinetic and potential energies both increase when bonds are broken KE is your temperature, PE reflects that

In comparisons, more energy lost means a more stable compound Because energy out = energy in

Kinetic and potential energies both decrease when bonds are formed

Kinetic and potential energies both increase when bonds are broken KE is your temperature, PE reflects that

In comparisons, more energy lost means a more stable compound Because energy out = energy in

Which kind of energy is stored in a chemical bond?

1) potential 2) kinetic

3) activation 4) ionization

As energy is released during the formation of a bond, the stability of the chemical system generally:

1) decreases

2) Increases

3) remains the same

Which kind of energy is stored in a chemical bond?

1) potential 2) kinetic

3) activation 4) ionization

As energy is released during the formation of a bond, the stability of the chemical system generally:

1) decreases

2) Increases

3) remains the same

Valence ElectronsValence Electrons

Valence electrons are in the outermost energy level of an atom, so higher energy

Elements in same period have same # valence electrons, so behave similarly

Valence involved in bonding, others stay back and relax

Valence electrons are in the outermost energy level of an atom, so higher energy

Elements in same period have same # valence electrons, so behave similarly

Valence involved in bonding, others stay back and relax

Major League Valence Electrons

Major League Valence Electrons

steady, reliable a little less predictable

wild, unpredictable

The Octet RuleThe Octet Rule

Noble gases are inert (inactive), very stable 8 valence electrons, complete octet 8 is most electrons that can be held in valence

shell All atoms want 8, and work to get there by

interacting with others Bonding is sharing or giving/receiving

electrons Stability found in complete octet

Noble gases are inert (inactive), very stable 8 valence electrons, complete octet 8 is most electrons that can be held in valence

shell All atoms want 8, and work to get there by

interacting with others Bonding is sharing or giving/receiving

electrons Stability found in complete octet

Exceptions to octet rule: H & He: only 2 electrons B & Al: will try for 8 electrons, but fine with 6 N: easy-going, can have less or more than 8 F: really electronegative, can take more than

8e-, bonds with nonmetal in Period 3 or lower Somewhat reactive noble gases (with F)

Exceptions to octet rule: H & He: only 2 electrons B & Al: will try for 8 electrons, but fine with 6 N: easy-going, can have less or more than 8 F: really electronegative, can take more than

8e-, bonds with nonmetal in Period 3 or lower Somewhat reactive noble gases (with F)

Lewis Electron Dot Structures

or Lewis Structures, or Lewis Diagrams

Lewis Electron Dot Structures

or Lewis Structures, or Lewis Diagrams Show valence

electrons for bonding

Chemical symbol surrounded by 1 to 8 “VE” dots

Symbol represents nucleus and non-VE, called a kernel

Show valence electrons for bonding

Chemical symbol surrounded by 1 to 8 “VE” dots

Symbol represents nucleus and non-VE, called a kernel

Two on top in S, then one at a time

Draw Lewis Structures for:

K Mn Sn Al At Kr C Si Pb

Draw Lewis Structures for:

K Mn Sn Al At Kr C Si Pb

Important Clarification About Lewis StructuresImportant Clarification About Lewis Structures

When placing electrons dots around a chemical symbol, the first two always go on top

BUT those are simply the first 2 of however many valence electrons are present

They are counted with the valence electrons, not separate

If an atom has 1 VE, only draw 1 dot, not 2 on top and then 1

When placing electrons dots around a chemical symbol, the first two always go on top

BUT those are simply the first 2 of however many valence electrons are present

They are counted with the valence electrons, not separate

If an atom has 1 VE, only draw 1 dot, not 2 on top and then 1

3 Types of Bonding3 Types of Bonding

Covalent: sharing of electrons

Ionic: giving and receiving of electrons

Metallic: distribution of electrons in metals




Types of Bonds:Covalent BondingTypes of Bonds:

Covalent Bonding

Covalent bondsCovalent bonds

Covalent bonds: atoms share electrons to achieve a stable octet

2 nonmetals, same or different elements

Remember: 2 electrons per bond 8 electrons (octet) = up to 4 bonds can

be formed (with exceptions)

Single/double/triple bonds Extra electrons as lone pairs

Covalent bonds: atoms share electrons to achieve a stable octet

2 nonmetals, same or different elements

Remember: 2 electrons per bond 8 electrons (octet) = up to 4 bonds can

be formed (with exceptions)

Single/double/triple bonds Extra electrons as lone pairs

Know That Lines Are Bonds!

Know That Lines Are Bonds!

7 single bonds 1 double bond & 2 single bonds

10 single bonds

Looks confusing,but same basicprinciple

- Reminder -- Reminder -

Electronegativity is a measure of the attraction of a nucleus for a bonded electron; how much an atom “wants” electrons

Electronegativity is a measure of the attraction of a nucleus for a bonded electron; how much an atom “wants” electrons

Rules for Lewis Diagrams of covalent bonds

Rules for Lewis Diagrams of covalent bonds

1. Count total # valence electrons in atoms of compound

2. Arrange atoms• Central usually has lowest

electronegativity, only present once, and isn’t H

3. Place single bonds

4. Add lone pair electrons to outsides, then center

5. Make more bonds if needed, using lone pairs







Draw Lewis structures for:• C2H2 •Water N2 •Ammonia

Draw Lewis structures for:• C2H2 •Water N2 •Ammonia







Draw the Lewis structure for

formaldehyde, CH2O


formaldehyde, CH2O1. Count total # valence

electrons in atoms of compound













hypobromous acid, HOBr


hypobromous acid, HOBr1. Count total # valence

electrons in atoms of compound












Polarity of covalent bonds & The 1.7 “Rule”

Polarity of covalent bonds & The 1.7 “Rule”

Bond polarity is a measure of differences in electronegativity (EN)

Nonpolar covalent: share electrons evenly, with same EN, like diatoms

Polar covalent: unequal sharing of electrons, different EN, bonded atoms become “+” and “-”

Bond polarity is a measure of differences in electronegativity (EN)

Nonpolar covalent: share electrons evenly, with same EN, like diatoms

Polar covalent: unequal sharing of electrons, different EN, bonded atoms become “+” and “-”

0.0

0.1 to ~1.7-1.9

“RULE” NOT ALWAYS TRUE!

1.7 Rule1.7 Rule

Electronegativity BondDifference Polarity

0.0 nonpolar covalent0.1 - 1.7 polar covalent

1.8 and up ionic

Which of the following bonds is the most polar in nature?

1) Cl2 2) HCl 3) HBr 4) HI

The bond in a diatomic nitrogen molecule (N2) is best described as

1) polar 2) nonpolar ionic

3) nonpolar covalent 4) polar ionic

Which of the following bonds is the most polar in nature?

1) Cl2 2) HCl 3) HBr 4) HI

The bond in a diatomic nitrogen molecule (N2) is best described as

1) polar 2) nonpolar ionic

3) nonpolar covalent 4) polar ionic

Molecular SubstancesMolecular Substances

Each atom of a molecular substance has the electron configuration of a noble gas

Can be solid/liquid/gas, depending on attractive forces

Properties associated with covalent bonding: generally soft, poor conductors of heat and electricity, low melting/boiling points

Each atom of a molecular substance has the electron configuration of a noble gas

Can be solid/liquid/gas, depending on attractive forces

Properties associated with covalent bonding: generally soft, poor conductors of heat and electricity, low melting/boiling points

Molecules may contain polar bonds without being polar themselves

Molecules may contain polar bonds without being polar themselves

C-O: 0.8 C-Cl: 0.6 O-H: 1.2 H-Cl: 1.0 N-H: 0.8

Symmetrical = nonpolar Asymmetrical = polar

Which electron dot diagrams represent polar molecules?

Which electron dot diagrams represent polar molecules?

Molecular ShapesMolecular Shapes

Linear Bent Pyramidal Tetrahedral

Remember: lone pairs influence shape!

Symmetry = nonpolar

Linear Bent Pyramidal Tetrahedral

Remember: lone pairs influence shape!

Symmetry = nonpolar

One Last Note About CovalentOne Last Note About Covalent

Network solids are covalently bonded compounds without truly individual molecules

They go on forever in repeating patterns of atomic structure

Can be “divided” into unit cells, simplest representation of larger shape

Network solids are covalently bonded compounds without truly individual molecules

They go on forever in repeating patterns of atomic structure

Can be “divided” into unit cells, simplest representation of larger shape

Unit cell…

…of a net-work solid.

NOTa net-worksolid.

Types of Bonds:Ionic Bonding

or“The Suspiciously

Generous Stranger”

Types of Bonds:Ionic Bonding

or“The Suspiciously

Generous Stranger”

Ionic BondingIonic Bonding Metal ion (+ cation) and a nonmetal ion (- anion) Positive and negative ions held together by

electrostatic attraction between opposite charges Causes high melting/boiling points,

hard/brittle substances, sometimes conductive

Metal ion (+ cation) and a nonmetal ion (- anion) Positive and negative ions held together by

electrostatic attraction between opposite charges Causes high melting/boiling points,

hard/brittle substances, sometimes conductive

IonsIons Formed when individual atoms lose or gain electrons to be like the

closest noble gas Metals low EN, nonmetals high EN

Metals lose valence e- (to the nonmetal)

and become cations (+) Nonmetals gain valence e- (from the metal)

and become anions (-) Oxidation numbers represent charges formed,

and the closest noble gas

configuration

Formed when individual atoms lose or gain electrons to be like the closest noble gas

Metals low EN, nonmetals high EN Metals lose valence e- (to the nonmetal)

and become cations (+) Nonmetals gain valence e- (from the metal)

and become anions (-) Oxidation numbers represent charges formed,

and the closest noble gas

configuration

Electrons (-) charged, soNegative charge = gain electronsPositive charge = loss electrons

ReminderReminder

Ionization energy: the amount of

energy needed to remove the

most loosely bound electron from a neutral

atom

-Sort of the inverse of electronegativity Metals have low IE, want to lose their electrons,

don’t put up a fight Nonmetals have high IE, want all the electrons

they can get, hold on for dear life

Ionization energy: the amount of

energy needed to remove the

most loosely bound electron from a neutral

atom

-Sort of the inverse of electronegativity Metals have low IE, want to lose their electrons,

don’t put up a fight Nonmetals have high IE, want all the electrons

they can get, hold on for dear life

Nonmetals gain e- & look like the closest noble gas to the right.

Metals lose e- to look like the closest previous noble gas.

Lewis Structures for ionsLewis Structures for ions

Electron loss/gain based on electronegativity values

Nonmetals pull electrons away from metals

Ions go Ions go in brackets, in brackets, with charge with charge superscriptsuperscript

Electron loss/gain based on electronegativity values

Nonmetals pull electrons away from metals

Ions go Ions go in brackets, in brackets, with charge with charge superscriptsuperscript

May use different colorsor symbols for “new”electrons

Lewis Structures for IonsLewis Structures for Ions

1. Count starting valence e- for each atom

2. Add or subtract electrons for ionic charge

3. Draw Lewis structures with new total electrons

∙Metals will have none, nonmetals will have 8

·Draw nonmetals’ added e- differently than original

4. Put brackets around the ion

5. Write charge as a superscript








Co Cr As Te Po O W2+ 3+ 3- 2- 4+ 2- 6+

Where do all the [M+]valence e- go?

Lewis Structures for Ionic Bonding

Lewis Structures for Ionic Bonding















NaCl MgO KBr PbI2

Polyatomic IonsPolyatomic Ions

Polyatomic ions have multiple atoms in a charged compound.

Receives e- from elsewhere to become stable

All individual atoms are not necessarily charged

Associate with other things by ionic bonding, but held together by covalent bonds

Polyatomic ions have multiple atoms in a charged compound.

Receives e- from elsewhere to become stable

All individual atoms are not necessarily charged

Associate with other things by ionic bonding, but held together by covalent bonds

Lewis Structures for Polyatomic Ions

Lewis Structures for Polyatomic Ions

-Polyatomic ions are held together by covalent bonds, but interact with other things by ionic bonding

Combined rules

1.Count all valence electrons, plus or minus any charge

*Add for (-), subtract for (+)

2.Follow steps for covalent

bonding

3.Add brackets and

superscript like ionic bonds

-Polyatomic ions are held together by covalent bonds, but interact with other things by ionic bonding

Combined rules

1.Count all valence electrons, plus or minus any charge

*Add for (-), subtract for (+)

2.Follow steps for covalent

bonding

3.Add brackets and

superscript like ionic bonds

NO3 PO4- 3- - NH4

+ClF2

+HSO4

1.7 +

0.0

0.1-1.6

Metallic BondsMetallic Bonds

Metals: few valence electrons and low ionization energies

Can mix, but don’t bond with

other metals Atoms fixed in crystalline lattice Valence e- in a “sea of mobile

electrons” Metallic bonds: force of attraction

of mobile VE for (+) atoms Like metal ion Whack-a-Mole

Metals: few valence electrons and low ionization energies

Can mix, but don’t bond with

other metals Atoms fixed in crystalline lattice Valence e- in a “sea of mobile

electrons” Metallic bonds: force of attraction

of mobile VE for (+) atoms Like metal ion Whack-a-Mole

Metallic Bond PropertiesMetallic Bond Properties

Good heat/electric conductivity Bonds are strong: high melting and boiling

points Malleability: metals can be hammered into

shapes Atoms move to new positions, but electrons stay

mobile

Which element has a crystalline lattice throughout which electrons flow freely?

1) Bromine 2) Calcium 3) Carbon 4) Sulfur

Good heat/electric conductivity Bonds are strong: high melting and boiling

points Malleability: metals can be hammered into

shapes Atoms move to new positions, but electrons stay

mobile

Which element has a crystalline lattice throughout which electrons flow freely?

1) Bromine 2) Calcium 3) Carbon 4) Sulfur

Metallic bonding animation:

http://www.youtube.com/watch?v=XHV9LzCH2KA

Metallic bonding animation:

http://www.youtube.com/watch?v=XHV9LzCH2KA

Other BondsOther Bonds

Savings bonds Get stronger over

time James Bond’s

Vary in strength from one to the next

Barry Bonds Also increase in

strength, but End up much

stronger than should ever occur naturally

Savings bonds Get stronger over

time James Bond’s

Vary in strength from one to the next

Barry Bonds Also increase in

strength, but End up much

stronger than should ever occur naturally

Distinguishing BetweenBond Types




-Nonmetal & nonmetal-Metal & nonmetal-Polyatomic ions & anything

Intermolecular ForcesIntermolecular Forces

Act between molecules, not within them like “real bonds”

Only in covalent compounds, not ionic or metal

Strong IMF give high boiling and melting points

Electrostatic attractions exist between ionic compounds

Act between molecules, not within them like “real bonds”

Only in covalent compounds, not ionic or metal

Strong IMF give high boiling and melting points

Electrostatic attractions exist between ionic compounds

DipolesDipoles

Polar molecules are dipoles (two distinct ends) Opposite charges temporarily attract by

dipole-dipole forces between covalent molecules

A dipole can “persuade” a nearby molecule to become an induced dipole

Dipole moment is the strength of attraction

Polar molecules are dipoles (two distinct ends) Opposite charges temporarily attract by

dipole-dipole forces between covalent molecules

A dipole can “persuade” a nearby molecule to become an induced dipole

Dipole moment is the strength of attraction

Hydrogen BondingHydrogen Bonding

Important enough to get its own slide Hydrogen bonds act between an H atom and

a nearby N, O, or F (3 very electronegative atoms)

Much stronger than dipole- dipole attractions Hold water molecules together, give H2O its high boiling point (high for a small molecule)

Hydrogen in polar molecules is basically a bare proton, attracted by N/O/F

Important enough to get its own slide Hydrogen bonds act between an H atom and

a nearby N, O, or F (3 very electronegative atoms)

Much stronger than dipole- dipole attractions Hold water molecules together, give H2O its high boiling point (high for a small molecule)

Hydrogen in polar molecules is basically a bare proton, attracted by N/O/F

chapter 6: bonding or a scientific drama. quick review what is a molecule? two or more atoms...

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