Chemical Bonding Covalent Bonding – Part I Ball-and-stick model.

ChemicaChemical l

BondingBondingCovalent Bonding – Covalent Bonding –

Part IPart I

Ball-and-stick model

•Part I: Molecules vs. Ionic Part I: Molecules vs. Ionic Compounds; Lewis Dot and Compounds; Lewis Dot and Structural FormulasStructural Formulas

•Part II: Molecular Geometry Part II: Molecular Geometry •Part III: Naming molecular Part III: Naming molecular

compoundscompounds

Part 1: Essential Part 1: Essential QuestionsQuestions

• How do covalent molecules bond How do covalent molecules bond differently from ionic compounds?differently from ionic compounds?

• Does this difference in bonding affect the Does this difference in bonding affect the physical properties of ionic compounds physical properties of ionic compounds and covalent molecules?and covalent molecules?

• What does a molecular formula tell us?What does a molecular formula tell us?• What do these molecular compounds What do these molecular compounds

look like?look like?

Bonds are…Bonds are…Forces that hold groups of atoms together Forces that hold groups of atoms together

and make them function as a unit. and make them function as a unit.

Two types:Two types: Ionic bondsIonic bonds – – transfertransfer of electrons of electrons

Covalent bondsCovalent bonds – – sharingsharing of electrons. of electrons. The resulting particle is called a The resulting particle is called a ““moleculemolecule””

Covalent BondsCovalent Bonds• The word The word covalentcovalent is a is a

combination of the prefix combination of the prefix co-co- (from Latin (from Latin comcom, meaning , meaning ““withwith”” or or ““togethertogether””), and the verb ), and the verb valerevalere, meaning , meaning ““to be strongto be strong””..

• Two electrons shared together Two electrons shared together have the strength to hold two have the strength to hold two atoms together in a bond.atoms together in a bond.

MoleculesMolecules Many Many elementselements found in nature found in nature

are in the form of are in the form of moleculesmolecules:: a a neutral group of atomsneutral group of atoms joined joined

together by together by covalent bondscovalent bonds.. For example, air contains oxygen For example, air contains oxygen

molecules, consisting of two molecules, consisting of two oxygen atoms joined covalently oxygen atoms joined covalently is called a is called a ““diatomicdiatomic molecule molecule”” (O(O22))

How does HHow does H22 form? form?

• The nuclei repel each other, The nuclei repel each other, since they both have a positive since they both have a positive charge (like charges repel).charge (like charges repel).

++

(diatomic hydrogen molecule)

+ +

How does HHow does H22 form? form?

++

•But, the nuclei are attracted But, the nuclei are attracted to the electrons to the electrons

•Molecules Molecules shareshare the the electrons, and this is called a electrons, and this is called a ““covalent bondcovalent bond””, and , and involves only involves only NONMETALSNONMETALS!!

Covalent bondsCovalent bonds•NonmetalsNonmetals hold on to their hold on to their

valence electrons.valence electrons.• They canThey can’’t give away electrons to t give away electrons to

bond.bond.– But still want But still want noble gasnoble gas configuration. configuration.

• Get it by Get it by sharing valence electronssharing valence electrons with each other = with each other = covalent bondingcovalent bonding

• By sharing, By sharing, both atomsboth atoms get to get to count the electrons toward a noble count the electrons toward a noble gas configuration.gas configuration.

Covalent bondingCovalent bonding

• Fluorine has seven valence Fluorine has seven valence electrons (but would like to have 8)electrons (but would like to have 8)

F

Covalent bondingCovalent bonding

• Fluorine has seven valence Fluorine has seven valence electronselectrons

• A second atom also has sevenA second atom also has seven

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence

electrons A second atom also has seven By sharing electrons…

F F

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons…

…both end with full orbitals

F F

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F8 Valence electrons

Covalent bonding Fluorine has seven valence electrons A second atom also has seven By sharing electrons… …both end with full orbitals

F F8 Valence electrons

Properties of Molecular Properties of Molecular CompoundsCompounds

• Molecular compounds tend to Molecular compounds tend to have relatively have relatively lowerlower melting and melting and boiling points than ionic boiling points than ionic compounds – this is compounds – this is not as strong not as strong a bond as ionica bond as ionic

• Molecular compounds tend to be Molecular compounds tend to be gases or liquidsgases or liquids at room at room temperaturetemperature– Ionic compounds were solidsIonic compounds were solids

Properties of Covalent Properties of Covalent compoundscompounds

State at room tempState at room temp Liquids or gasesLiquids or gases

StructureStructure No generalizationNo generalization

Melting PointMelting Point Lower than ionic Lower than ionic cmpdscmpds

Boiling PointBoiling Point Lower than ionic Lower than ionic cmpdscmpds

Electrical Electrical conductivityconductivity

NoneNone

Solubility in waterSolubility in water Depends on polarity Depends on polarity but generally notbut generally not

How can you tell ionic vs How can you tell ionic vs covalent?covalent?

• LetLet’’s take a moment and make sure s take a moment and make sure we recognize the difference between we recognize the difference between ionic and covalent compoundsionic and covalent compounds

• http://www.youtube.com/watch?v=PKA4CZwbZWU (Tyler Dewitt – 8:51 min) (Tyler Dewitt – 8:51 min)

• Flip to the last page and complete the Flip to the last page and complete the Types Of Chemical Bonds worksheet.Types Of Chemical Bonds worksheet.

• A molecular compound has a A molecular compound has a molecular formula:molecular formula:– Shows Shows how many atomshow many atoms of each of each

element a molecule containselement a molecule contains

Molecular FormulasMolecular Formulas

Molecular FormulasMolecular Formulas• The formula for water is written as The formula for water is written as

HH22OO– The subscript The subscript ““22”” behind hydrogen behind hydrogen

means there are 2 atoms of hydrogen; means there are 2 atoms of hydrogen; if there is only one atom, the subscript if there is only one atom, the subscript 1 is omitted1 is omitted

• Molecular formulas Molecular formulas DO NOTDO NOT tell any tell any information about the information about the structurestructure (the (the arrangement of the various atoms). arrangement of the various atoms).

- Page 215

These are some of the different ways to represent ammonia:

1. The molecular formula shows how many atoms of each element are present

2. The structural formula ALSO shows the arrangement of these atoms!

3. The ball and stick model is the BEST, because it shows a 3-dimensional arrangement.

Structural FormulasStructural Formulas

Now the fun part,Now the fun part,

• LetLet’’s first start with drawing Lewis s first start with drawing Lewis Dot Diagrams and then convert Dot Diagrams and then convert them to structural formulas!them to structural formulas!

Example: Water, HExample: Water, H22OO

Example: Phosphorus trichloride, PCl3

Structural FormulasStructural Formulas

• Structural formulasStructural formulas are a graphic representation of the molecular are a graphic representation of the molecular structure, showing how the atoms are structure, showing how the atoms are arranged and connectedarranged and connected. . – Uses lines to indicate bondsUses lines to indicate bonds– And dots to represented unbonded electronsAnd dots to represented unbonded electrons

Structural FormulasStructural Formulas

• Now write HNow write H22O and PClO and PCl33 as as structural formulasstructural formulas

Bond typesBond types

• Our two examples involved only Our two examples involved only single bonds.single bonds.

• Single bonds are when Single bonds are when two two electronselectrons are shared between two are shared between two atoms, they form a single bond. 2 atoms, they form a single bond. 2 dots = 1 bonddots = 1 bond

Bond TypesBond Types• Sometimes atoms share Sometimes atoms share more more

thanthan one pairone pair of valence of valence electrons.electrons.

• A A double bonddouble bond is when atoms is when atoms share share two pairstwo pairs of electrons (4 of electrons (4 total)total)

• A A triple bondtriple bond is when atoms is when atoms share share three pairsthree pairs of electrons of electrons (6 total)(6 total)

Is there an easier way?Is there an easier way?

• Do we need to draw out the Lewis Do we need to draw out the Lewis Dot Diagrams each time or is Dot Diagrams each time or is there an easier way?there an easier way?

Writing Structural Writing Structural FormulasFormulas

1.1. Sum the number of valence electrons each atom Sum the number of valence electrons each atom ideally ideally wantswants..

2.2. Subtract the sum of the number of valence Subtract the sum of the number of valence electrons each atom electrons each atom hashas..

3.3. Divide by 2Divide by 2

4.4. Answer = number of bondsAnswer = number of bonds

5.5. Now, figure out how to place them!Now, figure out how to place them!

6.6. Fill in the rest of the unbonded valence electrons Fill in the rest of the unbonded valence electrons with dots to give each atom a full octet.with dots to give each atom a full octet.

ExampleExample

N

H

WantsWants

HasHas

BondsBonds

Structural Formula for Structural Formula for COCO22

WantsWants

HasHas

BondsBonds

Example: HCNExample: HCN

• HCN: C is central atomHCN: C is central atom

WantsWants

HasHas

BondsBonds

Practice: CF4

WantsWants

HasHas

BondsBonds

Practice: SO2

WantsWants

HasHas

BondsBonds

Diatomic MoleculesDiatomic Molecules

• Seven elements exist as Seven elements exist as homonuclear diatomic molecules at room temperaturediatomic molecules at room temperature

• They are They are more stablemore stable this way than as this way than as individual atoms! individual atoms!

• Diatomic molecules: Diatomic molecules: HH22 O O22 N N2 2 ClCl22 F F22 I I22 Br Br22

• LetLet’’s see how they bonds see how they bond

Diatomic MoleculesDiatomic Molecules

BBC Bitesize video to recap

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/atomic/covalentbond.shtml

STOPSTOP

• Now practice on your own by Now practice on your own by completing the Structural practice completing the Structural practice problems.problems.

Part II: Molecular Part II: Molecular GeometryGeometry

Essential QuestionsEssential Questions

1.1. Okay, these structural diagrams Okay, these structural diagrams are two dimensions. What do are two dimensions. What do these molecules really look like?these molecules really look like?

2.2. Do the bonds and lone pairs repel Do the bonds and lone pairs repel each other? And if yes, what each other? And if yes, what does this do to the shape of does this do to the shape of these molecules? these molecules?

Molecular geometryMolecular geometry• The shape of a molecule is determined by The shape of a molecule is determined by

the the number of electron groupsnumber of electron groups located located around the central atom.around the central atom.

• Electrons are negatively charged, so they Electrons are negatively charged, so they repel each other.repel each other.

• This causes molecules to take a shape with This causes molecules to take a shape with the the maximum distancemaximum distance between electron between electron pairs.pairs.

• Theory is called Theory is called VSEPRVSEPR

VSEPR: stands for...VSEPR: stands for...•VValence alence SShell hell EElectron lectron PPair air

RRepulsionepulsion• Predicts the three dimensional shape Predicts the three dimensional shape

of molecules.of molecules.• The name tells you the theory:The name tells you the theory:

– Valence shell = outside electrons.Valence shell = outside electrons.– Electron Pair repulsion = electron pairs Electron Pair repulsion = electron pairs

try to get try to get as far awayas far away as possible from as possible from each other.each other.

• Can determine the Can determine the angles of bondsangles of bonds..

Molecular geometryMolecular geometryTo determine the shape, we look at the To determine the shape, we look at the

central atom and answer to questions.central atom and answer to questions.• How many atoms are bonded to the How many atoms are bonded to the

central atom?central atom?• How many lone pairs are on it?How many lone pairs are on it?

https://ed.ted.com/lessons/what-is-the-shape-of-a-molecule-george-zaidan-and-charles-morton

(3:47)

LinearLinearOne or two atoms bonded to the One or two atoms bonded to the

central atom and no lone pairscentral atom and no lone pairs

Two dimensional Two dimensional

Trigonal planarTrigonal planar• Three atoms Three atoms

bonded to bonded to central atom central atom with no lone with no lone pairspairs

• Think of a Think of a triangle all in triangle all in one plane (2 one plane (2 dimensional)dimensional)

TetrahedralTetrahedral

• Four atoms Four atoms bonded to the bonded to the central atomcentral atom

• Want to get as far Want to get as far away from each away from each other as possible!other as possible!

• Three Three dimensionaldimensional

Trigonal pyramidalTrigonal pyramidal• Three atoms bonded to the central Three atoms bonded to the central

atom and one set of lone pair atom and one set of lone pair electrons.electrons.

• Think of tetrahedralThink of tetrahedral’’s bottoms bottom

BentBent

• Two atoms bonded and two sets of Two atoms bonded and two sets of lone pairs. lone pairs.

• Think of tetrahedral missing two Think of tetrahedral missing two legs.legs.

Molecular geometryMolecular geometryAtoms Atoms bonded to bonded to central central atomatom

Lone Lone pairspairs

ShapeShape Bond Bond angleangle

1 or 21 or 2 00 LinearLinear 180180

33 00 Trigonal Trigonal planarplanar

120120

44 00 TetrahedralTetrahedral 109.5109.5

33 11 Trigonal Trigonal pyramidalpyramidal

107107

22 22 bentbent 104.5104.5

Are those the only Are those the only shapes?shapes?

VSEPRVSEPRHow do we figure this out?How do we figure this out?

1.1. Calculate Calculate number of bondsnumber of bonds

2.2. Draw the Draw the structural diagramstructural diagram

3.3. Determine the molecular Determine the molecular shapeshape

4.4. Draw the Draw the molecular shapemolecular shape

How do we draw 3D?How do we draw 3D?

Example: Methane, Example: Methane, CHCH44

• Wants 8 + 4(2) = 16 Wants 8 + 4(2) = 16 • Has 4 + 4(1) = 8Has 4 + 4(1) = 8

• (16-8)/2 = 4 bonds(16-8)/2 = 4 bonds

VSEPR for methane (a VSEPR for methane (a gas):gas):

• Single bonds fill Single bonds fill all atoms.all atoms.

• There are 4 There are 4 pairs of pairs of electrons electrons pushing away.pushing away.

• The furthest The furthest they can get they can get away is away is 109.5º109.5º

C HH

H

H

This 2-dimensional drawing does not show a true representation of

the chemical arrangement.

4 atoms bonded4 atoms bonded• Basic shape is Basic shape is

tetrahedraltetrahedral..• A pyramid A pyramid

with a with a triangular triangular base.base.

• Same shape Same shape for everything for everything with 4 pairs.with 4 pairs.

CH HH

H 109.5º

Example: Example: Ammonia Ammonia (NH(NH33) )

Example: Water (HExample: Water (H22O)O)

Example: Carbon disulfide, Example: Carbon disulfide, CSCS22

Model Set ActivityModel Set ActivityFor this activity, you will work with a partner For this activity, you will work with a partner

to:to:

1.1. Calculate the number of bondsCalculate the number of bonds

2.2. Draw the structural diagramsDraw the structural diagrams

3.3. Build the molecule with the model setBuild the molecule with the model set

4.4. Check it with the teacherCheck it with the teacher

5.5. Draw a 3D version on your paperDraw a 3D version on your paper