Covalent Bonding Molecular Compoundsgcit.org/ourpages/auto/2014/12/21/48018400/Per 1-2...2014/12/21 · Per 1 2 covalent bonding.notebook 36 December 19, 2014 Drawing Lewis Structures

Per 12 covalentbonding.notebook

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December 19, 2014

Covalent Bonding

and Molecular Compounds

Smith


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December 19, 2014

Covalent Bonding & Molecular Geometry

Examine these two forms of the same compound, ibuprofen.


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December 19, 2014


This form of ibuprofen has virtually no

antiinflammatory effect.

This form of ibuprofen is about 100x more effective at

alleviating pain than the other form.

Even though they consist of the exact same number and kinds of atoms, these two molecules have very different chemical properties.


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December 19, 2014

In this unit, we will explore what causes molecules to have various shapes. Later, we will then examine how molecular

geometry affects different chemical properties.


Take a look around you. The chemistry of everything you see, hear, feel, touch and taste is a result of not only what it's made of but also how it's put together.(Remember this for next year in biology!)


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December 19, 2014

Chemical Bonds

Ionic The electrostatic attraction between ions

Covalent The sharing of electrons between atoms

Metallic Each metal atom bonds to other metals atoms within a "sea" of electrons (covered in a later unit)

There are three basic types of bonds:


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December 19, 2014

1 Chlorine monoxide is

A ClO2

B ClO

C OCl

D O2Cl

E I don't know how to answer this.


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December 19, 2014

Chemical Bonds

Ionic BondingIonic bonds occur when the difference in electronegativity between

two atoms is more than 1.7.

Covalent BondingIf the difference of electronegativity is less than 1.7, neither atom

takes electrons from the other; they share electrons. This type of bonding typically takes place between two nonmetals.


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December 19, 2014

In the case of ionic bonding, a 3D lattice of ions is the result...not individual molecules. The chemical formula for an ionic compound is just the ratio of each type of ion in the lattice, not a particular number of ions in a molecule.

In contrast, covalent bonding results in individual molecules; each with its own unique shape. These shapes help determine the physical and chemical properties of everything around us!

Ionic v. Covalent Bonding

click here for an animationabout ionic and covalent bonding


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December 19, 2014

2 Which pair of atoms will form a covalent bond?

A Li and NeB K and Br

C C and O

D Na and Cl



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December 19, 2014

3 Which pair of atoms will form a covalent bond?

A Li and IB Na and ClC K and FlD H and O

E

I don't know how to answer this.


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December 19, 2014

Molecular Compounds

Covalent compounds are formed between two nonmetals.

When atoms are bonded covalently, the atoms are held together by sharing electrons. Such a compound is called a molecular compound which is also known as a molecule.

In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. Both atoms used the shared electrons to reach that goal.


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December 19, 2014

Naming Binary Molecular Compounds

Use prefixes to indicate the number the atoms

All end in "ide"

Examples

NO2 nitrogen dioxide

P2O5 diphosphorous pentoxide ( pentaoxide>pentoxide)


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December 19, 2014

Naming Binary Molecular Compounds

Look on your reference sheets for the prefixes.

The atom with the lower electronegativity is usually written first.

If there is only one of the first atom, the mono is left off.

Examples

CO carbon monoxide

CO2 carbon dioxide


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December 19, 2014

4 Chlorine monoxide is

A ClO2

B ClO

C OCl

D O2Cl



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December 19, 2014

5 Dinitrogen tetroxide is

A NO2

B N2O4

C NO3

D N4O2



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December 19, 2014

6 H2O is

A Hydrogen monoxide

B Dihydrogen monoxide

C Hydrogen oxide

D Hydrogen dioxide



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December 19, 2014

7 SO3 is

A sulfate B sulfur oxide

C sulfur trioxide

D sulfite



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December 19, 2014

8 MgO is

A monomagnesium monoxideB magnesium monoxideC monomagnesium oxideD magnesium oxideE I don't know how to answer this.


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December 19, 2014

9 P4O10 is

A Phosphorous pentoxide B Tetraphosphorous decoxide

C Phosphorous oxide

D PhosphateE I don't know how to answer this.


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December 19, 2014

Lewis structures are diagrams that show valence electrons as dots. Lewis structures are also known as Lewis dot or electron dot diagrams.

Note that no electrons are paired until after the fourth one.

Lewis Structures


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December 19, 2014

10 How many valence electrons does nitrogen have?

A 2B 3

C 4

D 5

E 7

F I don't know how to answer this.


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December 19, 2014

11 The Lewis structure for nitrogen is NTrue

False


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December 19, 2014

Recall that atoms tend towards having the electron configuration of a noble gas.For most atoms, that means having 8 valence electrons. The Octet Rule also applies to molecular compounds.

In covalent bonding, an atom will share electrons in an effort to obtain eight electrons around it (except hydrogen which will attempt to obtain 2 valence electrons).

The Octet Rule

A pair of valence electrons that is not shared between atoms is called an unshared pair, also known as a lone pair or a nonbonding pair.

Exceptions to the Octet Rule

H needs 2e

Be needs 2e

B needs 2e


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December 19, 2014

How do electron dot structures represent shared electrons?

Two atoms held together by sharing a pair of electrons are joined by a single covalent bond.

H + H H H

Hydrogen atom

Hydrogen atom

Hydrogen molecule

Shared pair of electrons

H

H

1s

1sHydrogen molecule


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December 19, 2014

How do electron dot structures represent shared electrons?

An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots.

H + H H H

Hydrogen atom

Hydrogen atom

Hydrogen molecule


H

H

1s

1sHydrogen molecule


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December 19, 2014

Structural Formulas

A structural formula represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms. As in the example below, one shared pair of electrons is represented by one dash.

HH

Hydrogen molecule


H H


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December 19, 2014

12 How many electrons are shared by two atoms to create a single covalent bond?

A 2

B 1


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December 19, 2014

The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.

Single Covalent Bonds

F F F F F F+ −−> OR

Fluorineatom

Fluorine molecule

Fluorineatom

1s

2s

2p

1s

2s

2p

Fluorine molecule


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December 19, 2014

In a water molecule, each hydrogen and oxygen atom attains a noblegas configuration by sharing electrons.

Lewis Structure of H2O

The water molecule has two unshared, or lone, pairs of electrons.

2 H + O > O H or O HH

HHydrogen atoms

Oxygen atom

Water molecule

1s 2p2s

1s 1s

O

H H

Water molecule


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December 19, 2014

In the ammonia molecule, NH3, each atom attains a noblegas configuration by sharing electrons.

This molecule has one unshared pair of electrons.

Lewis Structures of NH3

3 H + N > N H or N H

H

H

HHydrogen atom

Nitrogen atom Ammonia

molecule

1s 2p2s

1s 1sH

N

H1s

Ammonia molecule

H


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December 19, 2014

Drawing Lewis Structures

First, find the total number of valence electrons in the

polyatomic ion or molecule.

If it is an anion, add an electron for each negative charge.

If it is a cation, subtract an electron for each positive charge.

The P atom has 5 valence electrons.

A Cl atom has 7, and there are three of them.

The total number of valence electrons is:


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December 19, 2014


The central atom is the least electronegative element (excluding hydrogen).

Connect the other atoms to it by single bonds.

P has an electronegativity of 2.1 and Cl has an electronegativity of 3.0,

P will be the central atom.

The Cl atoms will surround the P atom.

The single bonds are shown as single lines.


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December 19, 2014

1. Count each single bond as a pair (two) of electrons.

2. Add electons to the outer atoms to give each one 8 (a full shell), or just 2 electrons for hydrogen.

3. Do the same for the central atom.

4. Check: Does each atom have a full outer shell (8 except, 2 for hydrogen)?

Have you used up all the valence electrons? Have you used too many electrons?



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December 19, 2014


First, find the total number of valence electrons in the polyatomic ion or molecule.

If it is an anion, add an electron for each negative charge.

If it is a cation, subtract an electron for each positive charge.

The N atom has 5 valence electrons

and

each of the three H atoms has 1 so the total number of valence electrons is,

NH3

5 + 3(1) = 8


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December 19, 2014


The central atom is the least electronegative element (excluding hydrogen because it can only have one bond).

Connect the other atoms to it by single bonds.

H can never be the central atom so N must be

The H atoms will surround the N atom.

The single bonds are shown as single lines.

HN HH

NH3


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December 19, 2014


HN HH

Each H already has two electrons, so that's done. But we have to add electrons to N to make 8.

HN HH

Count each single bond as a pair (two) electrons. Now add electons to the outer atoms to give each one a full shell (2 in the case of H).

Next, do the same for the central atom.

Check:Does each atom have a full outer shell ?

Have you used up all the valence electrons you started with? Have you used too many electrons?


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

CH4 Draw a Lewis Structure

H

H

HC

H

Check to make sure that each atom has a full outer shell.

Slide for Answer

C

H

H

H

H


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

NF3Draw a Lewis Structure

N F

F

F


Slide for Answer

N

F

F

F


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

SiF4Draw a Lewis Structure

F

Si

F

F F


Slide for Answer

Si


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December 19, 2014

Lewis Structures for ions

If you are drawing the Lewis Structure for an ION...

A negative ion has extra electrons, add the charge of the ion to your valence electron count.

ClO2 has 1(7) + 2(6) + 1 = 20 electrons

A positive ion is missing electrons, subtract the charge of the ion to your valence electron count.

NH4+ has 1(5) + 4(1) 1 = 8 electrons


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

PO43 Draw a Lewis Structure

O

P

O

O O


Slide for Answer

PO

O

O

O


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December 19, 2014

Lewis Structures

Draw the Lewis dot structure for the sulfate ion, SO4 2


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December 19, 2014

Lewis StructuresDraw the Lewis dot structure for the hydronium ion, H3O+


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December 19, 2014

C

NCl

F

OSB

P

I

H

CO OSi

SeXe

CO2Draw a Lewis Structure

We ran out of electrons, but carbon does not have an octet

yet!

Now What?

Slide for AnswerCO O


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December 19, 2014

Double and Triple Covalent Bonds

Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.

A bond that involves two shared pairs of electrons is a double covalent bond.

A bond formed by sharing three pairs of electrons is a triple covalent bond.


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December 19, 2014

Carbon Dioxide, CO2

1. Determine the # of valence electrons.

1 (4) + 2 (6) = 16 e

2. Form single bonds.This leaves 12 electrons, 6 pairs

3. Place lone pairs on oxygen atoms to give each 8.

Double and Triple Covalent Bonds

O C O

O C O


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December 19, 2014

O C O

Carbon Dioxide, CO2

4. Check: We had 16 electrons to work with; how many have we used?

5. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O.

Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with another bond.

O C O

O C O


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December 19, 2014

Covalent Bond Length


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December 19, 2014

Covalent Bond Energy

It requires more energy to break double and triple bonds compared to single bonds.

Triple bonds are the strongest of the three.

Bond Type Bond Energy

C C

C C

C C

348 kJ

614 kJ

839 kJ

Bond Type Bond Energy

N N 163 kJ

418 kJ

941 kJ

N N

N N


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December 19, 2014

Covalent Bond Energies


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December 19, 2014

Covalent Bonds Comparison

Type of Bond

Electrons shared

BondStrength

BondLength

2

4

6

weak

intermediate

strong

long

intermediate

short


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December 19, 2014

13 As the number of bonds between a pair of atoms increases, the distance between the atoms:

A increases

B decreases

C remains unchanged

D varies, depending on the atoms

E I don't know how to answer this


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December 19, 2014

14 As the number of bonds between a pair of atoms increases, the strength of the bond between the atoms:

A increases

B decreases

C remains unchanged




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December 19, 2014

15 As the number of bonds between a pair of atoms increases, the energy of the bond between the atoms:

A increases

B decreases

C remains unchanged




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December 19, 2014

16 How many electrons are shared by two atoms to create a single bond?


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December 19, 2014

17 How many electrons are shared by two atoms to create a double bond?


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December 19, 2014

18 How many electrons are shared by two atoms to create a triple bond?


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December 19, 2014

If you run out of electrons before the central atom has an octet……form multiple bonds until it does.

Writing Lewis Structures


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December 19, 2014

Oxygen molecule

Bonding of O2

1s

2s

2p

1s

2s

2p

O + O > O O or O O

O

O

Oxygenatom

Oxygenatom

Oxygenmolecule

Oxygenmolecule


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December 19, 2014

C

NCl

F

OSB

P

I

H

CSi

SeXe

CO Draw a Lewis Structure

Carbon has the lower electronegativity, so we will consider it the "central" atom...

O

Slide for Answer

C O


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December 19, 2014

Coordinate Covalent Bonds


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December 19, 2014

Coordinate Covalent BondsIn carbon monoxide, oxygen has a stable configuration but the carbon does not.

1s 2p2s

2s1s 2p

C + O −−> C O

Carbonatom Oxygen

atom

Carbonmonoxide

C

OCarbon monoxide molecule


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December 19, 2014

A coordinate covalent bond is a covalent bond in which one atom contributes both bonding electrons.

In a structural formula, you can show coordinate covalent bonds as arrows that point from the atom donating the pair of electrons to the atom receiving them.

In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.

Carbon has 4 valence electrons, oxygen has 6.

Coordinate Covalent Bonds


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

F2Draw a Lewis Structure

F F

Slide for Answer

F


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December 19, 2014

A molecule is a neutral group of atoms joined together by covalent bonds. Air contains oxygen molecules.

A diatomic molecule is a molecule consisting of two atoms. Certain elements do not exist as single atoms; they always appear as pairs.

When atoms turn into ions, this NO LONGER HAPPENS!

HydrogenNitrogenOxygenFluorineChlorineBromineIodine

Remember:HONClBrIF

Diatomic Molecules


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December 19, 2014

Return toTable ofContents

Resonance Structures


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December 19, 2014

C

NCl

F

OSB

P

I

H

Si

SeXe

O3Draw a Lewis Structure and use that to determine the VSEPR number

For the central oxygen:Electron domains = 3Bonding domains = 2Unpaired electrons = 1

Its VSEPR number is 3 2 1

O

O O

Slide for Answer

O O O

O O O


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December 19, 2014

Consider the Lewis structure we would draw for ozone, O3:

We would expect the double bond to have a shorter bond length than the single bond.

However, the true, observed structure of ozone shows that both OO bonds are the same length. How can this be?

Resonance

O

OO

O

O

O

[*]


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December 19, 2014

One Lewis structure cannot accurately depict a molecule like ozone. Therefore, we use multiple structures, called resonance structures, to describe the molecule.

Ozone has two resonance structures.

Resonance

O

O

OO

O

O

[*]


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December 19, 2014

ResonanceThe actual ozone molecule is a synthesis of these two resonance structures.

The bond length for both outer oxygen atoms falls somewhere between the single and double bond length.

O

O

OO

O

O

Resonancestructure

Resonancestructure

Ozone molecule

[*]


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December 19, 2014

Resonance

The nitrate ion, NO31 also requires resonance structures to explain

its covalent bonding.

There are three resonance structures for the nitrate ion:

[*]


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December 19, 2014

Draw the Lewis dot structure for SO3:

Resonance Structures

move for answer

[*]


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December 19, 2014

19 How many resonance structures can be drawn for the carbonate ion, CO32 ?

A 1B 2C 3D 4E 5

[*]

[This object is a pull tab]

Answer

C


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December 19, 2014

The benzene molecule is a regular hexagon of carbon atoms with a hydrogen atom bonded to each one. There are two resonance structures for benzene.

Benzene

Benzene, C6H6, is obtained from the distillation of fossil fuels. More than 4 billion pounds of benzene is produced annually in the United States. Because benzene is a carcinogen, its use is closely regulated.

[*]


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December 19, 2014

Localized v. Delocalized electronsIn truth, the shared pairs of electrons do not always remain between adjacent C atoms. They are not localized.

Instead, the electrons are said to be delocalized, meaning that they they can move around the 6carbon ring.

Benzene is commonly depicted as a hexagon with a circle inside to signify the delocalized electrons in the ring... we will talk more about this at the end of the year when we study organic chemistry.

<−−> or

[*]


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December 19, 2014


There are three types of ions or molecules that do not follow the octet rule:

#1 Ions or molecules with an odd number of electrons

#2 Ions or molecules with less than an octet

#3 Ions or molecules with more than eight valence electrons (an expanded octet)


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December 19, 2014

Though relatively rare and usually quite unstable and reactive, there are ions and molecules with an odd number of electrons.

NO is an example:

Exception 1: Odd Number of Electrons


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December 19, 2014

Exception 2: Fewer Than Eight Electrons

Beryllium (Be) this metal is shown to form molecular compounds, rather than ionic compounds as expected; only needs 4 electrons to be stable

Boron (B) only needs 6 electrons to be stable

Memorize these exceptions


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December 19, 2014

The only way PCl5 exists is if phosphorus has 10 electrons around it.

This is called an expanded octet.

Atoms on the third energy level or higher are allowed to expand their octet to 10 or 12 electrons.

The d orbitals in these atoms participate in bonding, allowing the expanded octet.

Exception 3: Expanded Octet


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December 19, 2014

How many electrons do these central atoms have around them?

Exception 3: Expanded Octet


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December 19, 2014

Draw the Lewis dot structure for phosphorous pentachloride, PCl5:



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December 19, 2014

Draw the Lewis dot structure for the xenon tetrafluoride, XeF4.



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December 19, 2014


Draw the Lewis dot structure for boron trifluoride, BF3:


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December 19, 2014

Draw the Lewis dot structure for the iodine tricholoride, ICl3.



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December 19, 2014

Polarity of BondsThough atoms often form compounds by sharing electrons, the electrons are not always shared equally. In a covalent bond, one atom has a greater ability to pull the shared pair toward it.


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December 19, 2014

Polarity of Bonds

Identical atoms will have an electronegativity difference of ZERO. As a result, the bond is NONPOLAR.


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December 19, 2014

Bonds and Electronegativity

Bond Type

NonPolar Covalent

Polar Covalent

Ionic

Electronegativity Difference

very small or zero

about 0.2 to 1.6

above 1.7 (between metal & nonmetal)


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December 19, 2014

Therefore, the fluorine end of the molecule has more electron density than the hydrogen end.

Polarity of Bonds

H F

We use the symbol to designate a dipole (2 poles). The "+" end is on the more positive end of the molecule and the arrow points towards the more negative end.


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December 19, 2014

When two atoms share electrons unequally, a bond dipole results.

Bond Dipoles and Electronegativity


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December 19, 2014

Polarity of Bonds

Compound Bond Electronegativity Dipole length (A0) Difference Moment (D)

HF 0.92 1.9 1.82HCl 1.27 0.9 1.08HBr 1.41 0.7 0.82HI 1.61 0.4 0.44

Bond lengths, Electronegativity, Differences and Dipole Moments of the Hydrogen Halides


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December 19, 2014

But just because a molecule possesses polar bonds does not mean the molecule as a whole will be polar.

Polarity of Molecules

For instance, in the case of CO2:

The polar bond is shown as a dipole, the arrow points to the more negative atom. Dipoles add as vectors.

[*]


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December 19, 2014


By adding the individual bond dipoles, one can determine the overall dipole moment for the molecule.

For a molecule to be polar, it must a) contain one or more dipoles AND b) have these polar bonds arranged asymmetrically

[*]

In other words, if all the dipoles are symmetrical, they will cancel each other out and the molecule will be

NONPOLAR.

Many molecules with lone pairs of electrons will be POLAR.


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December 19, 2014

These are some examples of polar & nonpolar molecules.


330, nonpolar

440, nonpolar

440, polar

431, polar110(?), polar

Slide for Answer

Slide for Answer Slide for Answer

Slide for AnswerSlide for Answer

[*]


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December 19, 2014

20 Which of these are polar molecules?

A a, bB a, b, cC a, cD a, c, dE c, e

[*]


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December 19, 2014

Documents

Covalent Bonding Molecular Compoundsgcit.org/ourpages/auto/2014/12/21/48018400/Per 1-2...2014/12/21 · Per 1 2 covalent bonding.notebook 36 December 19, 2014 Drawing Lewis Structures