Bonding powerpoint.ppt

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

Two Major Types of

Bonding

•

Ionic Bonding

– forms ionic _compounds – transfer of e

-•

Covalent

Bonding

-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

It’s the

mobile electrons

that enable m

e

tals to

ION

ic Bonding

• electrons are transferred between

valence shells of atoms • ionic compounds are

made of ions

• ionic compounds are called Salts or

Crystals

ION

ic bonding

• _Always formed between metals and non-metals

[METALS ]+ [NON-METALS ]

-Lost e

-ION

ic Bonding

• Electronegativity difference _{> 2.0}

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

NaCl CaCl₂

• _Compounds with polyatomic ions

• hard solid @ 22oC

• high mp temperatures

• _nonconductors of electricity in _solid phase

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

SALTS Crystals

Covalent Bonding

•

Pairs

of e- are

shared

between

non-metal

atoms

• electronegativity

difference

< 2.0

• forms polyatomic ions

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,

Ionic,

metallic

bonding?

• NO

• sodium

hydride

• Hg

• H

S

• sulfate

• NH

Drawing

ion

ic compounds

using Lewis Dot Structures

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

-NaCl

• This is the finished Lewis Dot Structure

[Na]

+

[ Cl ]

• 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

Draw the Lewis Diagrams

• LiF

Drawing

molecules

using

Lewis Dot Structures

• Symbol represents the KERNEL of the atom (nucleus and inner 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?

Methane CH

• This is the finished Lewis dot structure

• 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}

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”.

• DOUBLE bond

– atoms that share two e- pairs (4 e-)

O O

• TRIPLE bond

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

Draw Lewis Dot Structures

You may represent valence electrons

from different atoms with the following symbols x, ,

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

Draw Polyatomics

Types of

Covalent

Covalent

Bonds

Bonds

• NON-Polar

bonds

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

Between identical atoms

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

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

Polar molecules

(a.k.a.

Dipoles)

• Not equal on all sides

–Polar bond between 2 atoms makes a polar molecule

H

H

O



-

Water is

a

symmetrical

Water is a bent molecule

O

Making sense of the polar

non-polar thing

BONDS

Non-polar Polar Identical Different

MOLECULES

Non-polar Polar

IONIC bonds ….

Ionic bonds are so polar that the electrons are

not shared

C. Johannesson

VSEPR Theory

• Valence Shell Electron Pair Repulsion Theory

C. Johannesson

VSEPR Theory

• _{Types of e}- Pairs

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

-Lone pairs repel

1. Linear (straight line)

Ball and stick model

2. Bent

Ball and stick model

3.Trigonal pyramid

Ball and stick model

4.Tetrahedral

Ball and stick

• Attractions between

molecules

– van der Waals forces

• Weak 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

van der Waals periodicity

• increase with molecular mass.

• increase with closer distance between molecules

Hydrogen “Bonding”

• Strong polar attraction

– Like magnets

• Occurs ONLY

between H of one molecule and N, O, F of another

H is shared between

2 atoms of OXYGEN or

2 atoms of NITROGEN or

2 atoms of FLUORINE

Of 2

different

Why does H “bonding”

occur?

• Nitrogen, Oxygen and Fluorine

– small atoms with strong nuclear charges

• powerful atoms

Intermolecular forces

dictate chemical properties

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