ChemicalBONDING

Chemical Bond• A bond results from the attraction of nuclei

for electrons– All atoms trying to achieve a stable octet

• IN OTHER WORDS– the p+ in one nucleus are attracted to the e- of

another atom• Electronegativity

Bond Formation

• exothermic process

Energy released

ENERGY

Reactants

Products

Breaking Bonds

• Endothermic reaction– energy must be put into the bond in order

to break itENERGY 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 bonding

– Occurs between like atoms of a metal in the free state

– Valence e- are mobile (move freely among all metal atoms)

– Positive ions in a sea of electrons

• Metallic characteristics– High mp temps, ductile, malleable, shiny– Hard substances– Good 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

NaCl

CaCl2

• Compounds with polyatomic ionsNaNO3

• hard solid @ 22oC

• high mp temperatures

• nonconductors of electricity in solid phase

• good conductors in liquid phase or dissolved in water (aq)

SALTSCrystals

Properties of Ionic Compounds

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?

• NO2

• sodiumhydride

• Hg• H2S• sulfate

• NH4+

• Aluminum phosphate

• KH• KCl • 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 IONIC

– Determine which atom will be the +ion– Determine which atom will be the - ion

• Step 2– Write the symbol for the + ion first.

• NO DOTS

– Draw the e- dot diagram for the – ion• COMPLETE outer shell

• Step 3– Enclose both in brackets and show each charge

Draw the Lewis Diagrams• LiF

• MgO

• CaCl2

• K2S

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 1– count total valence e- involved

• Step 2– connect the central atom (usually the first in

the formula) to the others with single bonds • Step 3

– complete 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 O• TRIPLE 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 charge

REMEMBER! A positive charge means it LOST

electrons!!!!!

Draw Polyatomics

• Ammonium

• Sulfate

Types of CovalentCovalent BondsBonds• NON-Polar bonds

– Electrons shared evenly in the bond

– E-neg difference is zero

Between identical atomsDiatomic molecules

Types of Covalent BondsPolar bond

– Electrons unevenly shared– E-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 polarity

which is least and which is most?

• HCl

• CH4

• CO2

• NH3

• N2

• HF

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 sides– Polar 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 pyramidBall and stick model

Space filling model

Tetrahedral

Ball and stick model

Space filling model

• Attractions between molecules– van der Waals forces

• Weak attractive forces between non-polar molecules

– Hydrogen “bonding”• Strong attraction

between special polar molecules

Intermolecular attractions

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 molecules– Decreases when particles are farther away

Hydrogen “Bonding”• Strong polar

attraction– Like 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