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Power Point Presentation

Presented by

V.B.Kedar

Chemistry 1

F.Y.B.Sc

Chapter 3

Chemical Bonding

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-

IONic Bonding

• Electronegativity difference > 2.0

– Look up e-neg of the atoms in the bond

and subtract

NaCl

CaCl2

• Compounds with polyatomic ions

NaNO3

• 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

• sodium hydride

• 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 Covalent Bonds

• NON-Polar bonds

– Electrons shared evenly in the bond

– E-neg difference is zero

Between identical atoms Diatomic molecules

Types of Covalent Bonds Polar 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

H H C Draw Lewis dot first and

see 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 - +

H H O

-

+

Water is asymmetrical

+

Water is a bent molecule

O

H H H H

Making sense of the polar

non-polar thing

BONDS

Non-polar Polar

Identical Different

MOLECULES

Non-polar Polar

Symmetrical 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. Bent

Ball and stick

model

Space filling

model

3.Trigonal pyramid

Ball and stick

model

Space filling

model

4.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.

• 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

Thanks