( PRESENTATION )

CHEMICAL BOND

BOND FORMATION

exothermic process

Energy released

ENERGY

Reactants

Products

BREAKING BONDS

Endothermic reaction energy must be put into the bond in order to

break it

ENERGY Reactants

Products

Energy Absorbed

BOND STRENGTH Strong, STABLE bonds require lots of energy to

be formed or broken weak bonds require little E

TWO MAJOR TYPES OF BONDING

Ionic Bonding forms ionic compounds transfer of e-

Covalent Bonding forms molecules sharing e-

ONE MINOR TYPE OF BONDING

Metallic bondingOccurs between like atoms of a

metal in the free stateValence e- are mobile (move

freely among all metal atoms)Positive ions in a sea of electrons

Metallic characteristicsHigh mp temps, ductile, malleable,

shinyHard substancesGood conductors of heat and electricity

as (s) and (l)

It’s the mobile electrons that

enable me-tals to conduct

electricity!!!!!!

IONIC BONDING

electrons are transferred between valence shells of atoms

ionic compounds are made of ions

• ionic compounds are called Salts or Crystals

NOT MOLECULES

IONIC BONDING

Always formed between metals and non-metals

[METALS ]+ [NON-METALS ]

-

Lost e-Gained e-

IONIC BONDING Electronegativity difference > 2.0

Look up e-neg of the atoms in the bond and subtract

NaClCaCl2

Compounds with polyatomic ionsNaNO3

PROPERTIES OF IONIC COMPOUNDS

hard solid @ 22oC high mp temperatures nonconductors of electricity in solid phase good conductors in liquid phase or dissolved in

water (aq)

SALTSCrystals

COVALENT BONDING

Pairs of e- are shared between non-metal atoms

electronegativity difference < 2.0

forms polyatomic ions

molecules

PROPERTIES OF MOLECULAR SUBSTANCES

Low m.p. temp and b.p. temps

relatively soft solids as compared to ionic compounds

nonconductors of electricity in any phase

Covalent bonding

COVALENT, IONIC, METALLIC BONDING?

NO2sodiumhydride

HgH2Ssulfate

NH4+

Aluminum phosphate

KHKCl HF

• CO• Co

Also study your

characteristics!

DRAWING IONIC COMPOUNDS USING LEWIS DOT STRUCTURES

• Symbol represents the KERNEL of the atom (nucleus and inner e-)

• dots represent valence e-

NACL This is the finished Lewis Dot Structure

[Na]+ [ Cl ]-

How did we get here?

Step 1 after checking that it is IONICDetermine which atom will be the +ionDetermine which atom will be the - ion

Step 2Write the symbol for the + ion first.

NO DOTSDraw the e- dot diagram for the – ion

COMPLETE outer shell

Step 3Enclose both in brackets and show

each charge

DRAW THE LEWIS DIAGRAMS

LiFMgOCaCl2K2S

DRAWING MOLECULES USING LEWIS DOT STRUCTURES

Symbol represents the KERNEL of the atom (nucleus and inner e-)

dots represent valence e-

Always remember atoms are trying to complete their outer shell!

The number of electrons the atoms needs is the total number of bonds they can make.

Ex. … H? O? F? N? Cl? C? one two one three one four

METHANE CH4

This is the finished Lewis dot structure

How did we get here?

Step 1count total valence e- involved

Step 2connect the central atom (usually

the first in the formula) to the others with single bonds

Step 3complete valence shells of outer

atoms Step 4

add any extra e- to central atom

IF the central atom has 8 valence e- surrounding it . . YOU’RE DONE!

SOMETIMES . . . You only have two atoms, so there is no

central atom, but follow the same rules. Check & Share to make sure all the atoms

are “happy”.

Cl2 Br2 H2 O2 N2 HCl

DOUBLE bond atoms that share two e- pairs (4 e-)

O OTRIPLE bond

atoms that share three e- pairs (6 e-)

N N

DRAW LEWIS DOT STRUCTURES

You may represent valence electrons from different atoms with the following symbols x, ,

CO2

NH3

DRAW THE LEWIS DOT DIAGRAM FOR POLYATOMIC IONS Count all valence e- needed for covalent

bonding Add or subtract other electrons based on the

chargeREMEMBER!

A positive charge means it LOST electrons!!!!!

DRAW POLYATOMICS

Ammonium Sulfate

TYPES OF COVALENTCOVALENT

BONDSBONDSNON-Polar bonds

Electrons shared evenly in the bond

E-neg difference is zero

Between identical atomsDiatomic molecules

TYPES OF COVALENT

BONDS

Polar bondElectrons unevenly sharedE-neg difference greater than zero but

less than 2.0

closer to 2.0 more polar more “ionic

character”

PLACE THESE MOLECULES IN ORDER OF INCREASING BOND POLARITYWHICH IS LEAST AND WHICH IS MOST?

HClCH4

CO2

NH3

N2HF

a.k.a. “ionic character”

NON-POLAR MOLECULES

Sometimes the bonds within a molecule are polar and yet the molecule is non-polar because its shape is symmetrical. H

H

HH CDraw Lewis dot first andsee if equal on all sides

POLAR MOLECULES (A.K.A. DIPOLES)

Not equal on all sidesPolar bond between 2 atoms makes a polar molecule

asymmetrical shape of molecule

H Cl -+

ClH

SPACE FILLING MODEL“ELECTRON-CLOUD” MODEL

-+

HHO

-

+

WATER IS ASYMMETRICAL

+

WATER IS A BENT MOLECULE

O

H H H H

W - A - T - E - Ras bent as it can be!

Water’s polar MOLECULE!Water’s polar MOLECULE!

The H is positive The O is not - not - not - not

MAKING SENSE OF THE POLAR NON-POLAR THING

BONDS

Non-polar Polar

Identical Different

MOLECULES

Non-polar PolarSymmetrical

Asymmetrical

IONIC BONDS ….Ionic bonds are

so polar that the electrons are not shared but transferred between atoms forming ions!!!!!!

4 SHAPES OF MOLECULES

LINEAR (STRAIGHT LINE)

Ball and stick model

Space filling model

BENT

Ball and stick model

Space filling model

TRIGONAL PYRAMID

Ball and stick model

Space filling model

TETRAHEDRAL

Ball and stick model

Space filling model

INTERMOLECULAR ATTRACTIONS Attractions between

moleculesvan der Waals

forcesWeak attractive forces between non-polar molecules

Hydrogen “bonding”Strong attraction between special polar molecules

VAN DER WAALS Non-polar molecules can exist in liquid and

solid phases because van der Waals forces keep the

molecules attracted to each other

Exist between CO2, CH4, CCl4, CF4, diatomics and monoatomics

VAN DER WAALS PERIODICITY

increase with molecular mass. Greater van der Waals force?

F2 Cl2 Br2 I2

increase with closer distance between moleculesDecreases when particles are farther

away

HYDROGEN “BONDING”

Strong polar attractionLike magnets

Occurs ONLY between H of one molecule and N, O, F of another H “bond”

WHY DOES H “BONDING” OCCUR?

Nitrogen, Oxygen and Fluorine small atoms with strong nuclear charges

powerful atoms very high electronegativities

INTERMOLECULAR FORCES DICTATE CHEMICAL PROPERTIES

Strong intermolecular forces cause high b.p., m.p. and slow evaporation (low vapor pressure) of a substance.

WHICH SUBSTANCE HAS THE HIGHEST BOILING POINT?

HF NH3

H2O

WHY?

Fluorine has the highest e-neg, SO HF will experience the

strongest H bonding and

needs the most energy to weaken the i.m.f. and boil

THE UNUSUAL PROPERTIES OF WATER

Unusually high boiling point

Compared to other compounds in Group 16

DENSITY????

H2O(S) IS LESS DENSE THAN H2O(L)

The hydrogen bonding in water(l) molecules is random. The molecules are closely packed.

The hydrogen bonding in water(s) molecules has a specific open lattice pattern. The molecules are farther apart.

THE END