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

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-

• hard solid @ 22oC• high mp temperatures• nonconductors of electricity in solid

phase• good conductors in liquid phase or

dissolved in water (aq)

SALTS Crystals

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 StructuresYou 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 Covalent Bonds• NON-Polar bonds

–Electrons shared evenly in the bond–E-neg difference is zero

Between identical atoms Diatomic 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”

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 δ-δ+

HHO

δ-

δ+

Water is asymmetricalδ+

Water is a bent molecule

OH H H H

Making sense of the polar non-polar thing

BONDS

Non-polar PolarIdentical 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!!!!!!

C. Johannesson

VSEPR Theory• Valence Shell Electron Pair Repulsion

Theory

• Electron pairs orient themselves in order to minimize repulsive forces.

C. Johannesson

VSEPR Theory• Types of e- Pairs

– Bonding pairs - form bonds– Lone pairs - nonbonding e-

Lone pairs repel more strongly than

bonding pairs!!!

4 Shapes of molecules

1. Linear (straight line)Ball and stick model

Space filling model

2. BentBall and stick model

Space filling model

3.Trigonal pyramidBall and stick model

Space filling model

4.TetrahedralBall 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.

• 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”

H is shared between

2 atoms of OXYGEN or

2 atoms of NITROGEN or

2 atoms of FLUORINE

Of 2

different molecules

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 End