Chapter 8Covalent Bonding

Covalent bonding …….Covalent bonding …….

• Usually forms between two nonmetals (takers)

• Neither want to give up their electrons but are willing to share electrons

Exception: Hydrogen Exception: Hydrogen

Hydrogen and a nonmetal …..neither wants to give up their electrons and neither has enough pull to take the

other’s so they share a pair of electrons

•Hydrogen has one electron, but only needs one more to be “happy”

In a covalent bond the…In a covalent bond the…

-shared electrons are attracted to adjacent nuclei

+ +

                                                

  

Covalent BondingCovalent Bonding

Covalent Bonds form molecules

(* remember: Ionic Compounds form formula units)

Molecule = smallest part of a covalent compound

That’s That’s why…….Covalent why…….Covalent

compounds are also compounds are also called called molecularmolecular

compoundscompounds

Binary (2-element) compounds

-similar to ionic, but indicate the number of atoms using prefixes

Naming Covalent Naming Covalent CompoundsCompounds

Prefix Meaning

Mono- 1

Di- 2

Tri- 3

Tetra- 4

Penta- 5

Hexa- 6

Hepta- 7

Octa- 8

Nona 9

Deca- 10

-if only 1 atom of 1st element, then no prefix is used

Ex.

COCarbon monoxide

CO2

Carbon dioxide

-if more than 1 atom of 1st element, then use prefix

N2O4

Dinitrogen tetraoxide

Ws. Naming Molecular Compounds

Ws. Name the following Molecular Compounds

Hydrogen Compounds can form Acids

• Remember…..Hydrogen is the exception to most rules

• Hydrogen has 1 electron but only needs 1 more to be happy so it acts like a nonmetal

• Hydrogen doesn’t want to give up it’s one electron but it is willing to share it.

• When hydrogen combines with an anion a covalent compound is formed

When these compounds are dissolved in water…..

…..they become acids.

What makes them an acid?

• Hydronium ions are formed

•Start with ionic compound name.

•Then follow the 3 rules

How to Name AcidsHow to Name Acids

Naming AcidsNaming AcidsRule #1 (Binary Acids)Rule #1 (Binary Acids)

• When anion ends in “ide”, the acid name begins with “hydro” and then ends in “ic”, then “acid”

• Ex. Hydrogen chloride (HCl)= hydrochloric acid Hydrogen sulfide (H2S) =hydrosulfuric acid

Naming AcidsNaming AcidsRule #2 (Tertiary Acids)Rule #2 (Tertiary Acids)

• If anion ends in “ate”, the acid name is the stem of the anion with the suffix “-ic” followed by the word “acid”

• Ex. Hydrogen nitrate (HNO3) = nitric acid

Naming AcidsNaming AcidsRule #3 (Tertiary Acids)Rule #3 (Tertiary Acids)

•When anion ends in “ite” , the acid name is the stem of the anion with suffix “-ous” followed by the word “acid”

•Ex. Hydrogen sulfite (H2SO3) = sulfurous acid

Ws. Name the Following Acids

Ws. Formula Writing

MoleculeMolecule

• Ex. CO H2O

1 molecule of carbon monoxide

1 molecule of water

Coefficient – the # of molecules or # of formula units .

H2O

4 molecules of water

How many molecules of How many molecules of water???water???

4

The number covalent bonds The number covalent bonds that will form depends on the that will form depends on the

# of valence electrons# of valence electrons

*Remember each atom is trying to achieve noble gas configuration (full outer shell)

7 valence electrons wants to share 1 pair

6 valence electrons wants to share 2 pair

5 valence electrons wants to share 3 pair

Chlorine atoms each have 7

valence electrons

….they each want one more so they will share one pair of electrons

Formation of Bonds

Single Covalent BondsSingle Covalent Bonds – 1 shared – 1 shared pair of electronspair of electrons

Cl2

Single bond- 1 shared pair of Single bond- 1 shared pair of electronselectrons

F and F F F

Double bond-2 shared pairs of Double bond-2 shared pairs of electronselectrons

O and O O O

Triple bond-3 shared pairs of electronsTriple bond-3 shared pairs of electrons

N and N N N

-you show the shared pair(s) of electrons between symbolsEx. Cl2

Lewis Dot Diagram of Lewis Dot Diagram of Covalent CompoundsCovalent Compounds

Cl Cl

Structural FormulasStructural Formulas •Each pair of shared electrons is

shown as a dash( - )•Ex. Cl2

Cl Cl Cl-ClLewis Dot Diagram Structural Formula

*Remember hydrogen only needs to share one pair

Be Be carefulcareful with with Hydrogen (HHydrogen (H22))

Hydrogen (HHydrogen (H22))

H-H

Diatomic Diatomic MoleculesMolecules• Two different atoms covalently

bonded

• Ex. CO OH-

Diatomic Diatomic ElementsElements

Ex.

Cl and Cl

Cl Cl

-when atoms of same element covalently bond

Diatomic Diatomic ElementsElements-elements that exist in pairs when not bonded to other atoms

(“BrINClHOF”)Br2 bromine

I2 iodineN2 nitrogenCl2 chlorineH2 hydrogenO2 oxygenF2 fluorine

More examples of More examples of singlesingle covalent bonds…covalent bonds…

Water HWater H22OO(2 single covalent

bonds)

HO

H

Hydrogen and chlorineHydrogen and chlorine

H-Cl

Methane CHMethane CH4 4

( 4 single covalent bonds)( 4 single covalent bonds)

H

H C H

H

PClPCl3 3 Phosphorus Phosphorus trichloridetrichloride

( 3 single covalent bonds)( 3 single covalent bonds)

Cl P Cl

Cl

Double BondsDouble Bonds

O O

Lewis Dot Diagram of carbon Lewis Dot Diagram of carbon dioxidedioxide

O C O

Carbon dioxideCarbon dioxide

O C O

Triple bondsTriple bonds

N N

Coordinate Coordinate Covalent BondsCovalent Bonds

• A coordinate covalent bond is formed when one atom donates both electrons to be shared.

Ammonium NHAmmonium NH44++

N H

H

H H

Ammonia NH3Hydrogen

Coordinate covalent bond

In coordinate bond structural In coordinate bond structural formula……formula……

An arrow points from the atom donating the pair of electrons toward the atom receiving them.

N HH

H

H

When drawing electron dot diagrams……..

•if an atom is “short” 2 electrons – try a coordinate covalent bond

H3(PO4)

H3(PO4)

P O

O

O

OH

H H

Coordinate covalent bond

Bond PolarityBond Polarity•Nonpolar - When bonding electrons

are equally shared (same electronegativity)

• Ex. Diatomic elements

•Polar – When one atom has higher electronegativity ( attractive force) and pulls electron closer to it. It gains a slight negative charge and the other atom gains a slight positive charge

• Ex. H2O

Ws. What is Electronegativity?

.4 and below Nonpolar covalent

Between .4 to 2.0 Polar covalent

Greater than 2.0 ionic

• If the difference is….. the type of bond will be..

Electronegativity Differences !!!!!Electronegativity Differences !!!!!

Describing each bond in the molecule as ….

•Even pull= NonpolarUneven pull = polarStrong uneven pull = ionic

Showing polarity of individual bonds

Use differences in electronegativitiesIndicated with δ ( lower case Greek letter delta) and charge.

Overall polarity of Overall polarity of MoleculesMolecules

equals the sum of all the bond polarities

The arrow points to the atom with the higher electronegativity

Symmetry in MoleculesSymmetry in Molecules• Symmetrical molecules are

usually nonpolar. Polar bonds cancel each other out

• Ex. CO2

Carbon TetrachlorideCarbon Tetrachloride

Bonds can be polar, yet Bonds can be polar, yet overall molecular polarity is overall molecular polarity is

nonpolarnonpolar

Asymmetrical Asymmetrical MoleculesMolecules

• Asymmetrical molecules are polar if there are polar bonds in the structure.

• Ex. H2O

Polarity of WaterPolarity of Water

HH

O

δ - δ -

δ + δ +

VSEPR TheoryVSEPR Theory•Valence shell electron-pair repulsion theory

• Because electron pairs repel, molecules adjust shapes so that pairs are as far away from each other as possible

Domains

• Single bond • Double bond• Triple bond• Lone unshared pair

The # of Electron Domains The # of Electron Domains determines the Basic Electron determines the Basic Electron

Domain shapeDomain shape

• Linear – 1 or 2 domains• Trigonal Planar – 3 domains• Tetrahedral – 4 domains• Trigonal bipyramidal – 5 domains• Octrahedral – 6 domains

Linear

Trigonal Planar ( flat)

Tetrahedral

Trigonal bipyramidal

Octahedral

Determining the Electron Domain Shape

• Count up all valence electrons• Start with central atom (C, or Lowest EN, never H)• Place other atoms around with maximum repulsion• Put 8 electrons around outside atoms• Any extra electrons go around the central atom• Count the number of domains to determine the

basic shape

• **** some compounds do NOT follow the octet rule

Let’s try some• CS2

• BeH2

• CO2

• CH4

• CCl4• NO3

-

• NH4+

• SiF4

• SF4

Molecular geometry

• Shapes are altered if there are non- bonding pairs of electrons

surrounding the central atom

Bent – can be formed from a trigonal planar or tetrahedral

Ex. H2O

Ex. SO2

Trigonal Pyramidal- can be formed from a tetrahedral

Ex. NH3

Ws. Electron Domain and Molecular Geometries

Structures and ModelsStructures and Models

Covalent Bonding: Molecular Model

Building Lab

Model Colors

• Black – Carbon family• Blue – Nitrogen family• Red - Oxygen family• Green or Purple - Halogens• Yellow - Hydrogen

• Use sticks to show single bonds

• Use springs to show multiple bonds

Formula Electron domain shape/

Molecular shape

Lewis Dot diagram * be careful of shape

Single, double or triple bond ( list each bond

EN Difference- list for for each bond

Bond Type ( polar or nonpolar –list for each bond)

Polarity of Molecule (polar or nonpolar)

H2

EA=D=NBD=BD=

Cl2

EA=D=NBD=BD=

EA= valenceelectrons available D = electron domains

NBD= non-bonding domains BD= bonding domains

Electron –Domain Basic Bond Shapes

• Linear

• Bent

• Trigonal Planar

• Trigonal Pyramidal

• Tetrahedral

Hints for Lab

Start with Central Atom

• If it has carbon, use “C” as central atom

• If no carbon, use single atom or atom with lowest EN as central atom

• Never put hydrogen as central atom

Hints about the Acids

• Do polyatomic ion groups first, then add the hydrogens

• Use single atom, except Hydrogen, as central atom

• Usually contain coordinate covalent bonds

Last Hint !!!!

• If an atom is “short” 2 electrons – try a coordinate covalent bond

H2(CO3)

CO

O

ODouble bond

H H

H3(PO4)

P O

O

O

OH

H H

Coordinate covalent bond

H2(SO4)

S

O

OO

O

H

H

Coordinate covalent bonds

H(NO3)

N OO

OH

Coordinate covalent bond

Properties of Properties of Covalent Covalent

CompoundsCompounds• Low melting points (usually below

300oC) • Boiling points usually lower than

ionic compounds• Many are liquids or gases at room

temperature• High to low solubility• Poor to non-conducting

Covalent Compounds form Covalent Compounds form Network SolidsNetwork Solids

• Most covalently bonds substances melt easily because you just have to break the weak attractions between molecule and molecule

• Ex. Ice – Water– Sugar (C12H22O11)

Covalent crystalsCovalent crystals

• If covalent compound forms crystals (repeating pattern)……..

• Requires a lot of energy to break all the covalent bonds

• Have high melting points• Ex. diamonds

A diamond ( pure carbon)

Solubility of Solubility of Covalent Covalent

CompoundsCompounds•“Like dissolves Like”•Polar compounds will

dissolve in polar solvents•Nonpolar compounds will

dissolve in nonpolar solvents

Why don’t water and oil mix?

-Water is polar, oil is nonpolar.

-Water is more attracted to itself than to the oil.

Why do detergents cause water and oil to mix?-detergents are long molecules with one polar and one nonpolar end.

-the water is attracted to the polar end and the oil is attracted to the nonpolar end.

Soap and DetergentSoap and DetergentNonpolar end –attracts nonpolar oil or grease

Polar end –attracts (polar)water

Chapter ReviewCovalent Bonding

Ionic vs. CovalentElectrons transfer Electrons shared

Metal and Non metal Nonmetal and Nonmetal

Formula units molecules

No prefixes in names Prefixes in names

Neutral compound Neutral compound

Called salts If starts with “H” it could be an acid when dissolved in H2O

High melting points, easily dissolved and conduct when dissolved

Low melting points, not easy to dissolve, don’t conduct electricity

Ws. Bond Prediction

Ws.Naming Compounds

Ws. Name the Following Compounds

Ws. Naming Compounds Reference Sheet

Diatomics = 2 atoms of same element bonded

to each other

BrINClHOF

Diatomic element is linear and Nonpolar

Covalent Bonds – 4 Types• Single- 1 shared pair of electrons

(1 from each atom)

• Double – 2 shared pairs of electrons (two from each atom)

• Triple- 3 shared pairs of electrons, (three from each atom)

• Coordinate covalent – both electrons of shared pair come from 1 atom

Structural FormulaStructural Formula- shows arrangement of

bonds• Cl Cl single• O O double• N N triple• C O coordinate covalent

Electron Dot Diagrams

• Every atom MUST have 8 electrons drawn around it except “H”.

• “H” needs 2 electrons

Polar vs. Nonpolar – depends on EN

( electronegativity) difference

• Nonpolar – shared evenly – EN difference below .4

• Polar – shared unevenly – EN .4 – 2.0

• Ionic – pulls electron off of atom. EN above 2.0

Polarity of Bond

•Depends on electronegativity difference

Polarity of Molecule

• Look at symmetry, then polarity of the bonds

Know how to name ionic compounds, covalent compounds and acids

The End