bonding: an overview€¦ · atom a atom b bonding: underlying forces distance between nuclei y net...

Bonding: An Overview

LHSE Presents

Molecules and Compounds

Bonding: An Overview

• What is a bond?

• Bonding and Energy

– Bond Dissociation Energy

– Underlying Forces

• Types of bonds

– Covalent

– Polar Covalent

– Ionic

– Metallic

• Bonding Topics in other Lectures

What is a Bond?

A bond is the joining of two or more

atoms or ions under a force of attraction

When ANY atoms or ions join they

are considered a compound

before

after

Release

energy

Bonding and Energy

Reaction coordinate

Favorable

time

ener

gy

reactants

products

Activation

energy

Bonding and Energy

time

ener

gy

Consume

energy

before

after

Reaction coordinate

Unfavorable

bond

dissociation

energy

braking

bonds takes

energy!

Bonding and Energy

time

ener

gy

Consume

energy

before

after

Reaction coordinate

Unfavorable

+ +

- -

- -

-

-

1. Electrons (-) in Atom A are ATRRACTED to nucleus (+) in Atom B

2. Electrons (-) in Atom B are ATRRACTED to nucleus (+) in Atom A

3. Electrons (-) in Atoms A and B REPULSE each other

4. Nuclei (+) in Atoms A and B REPULSE each other

Atom A Atom B

Bonding: Underlying Forces

Distance between nuclei

Pote

nti

al E

ner

gy

Net attraction

Net repulsion

+

-

-

-

Bond length

Bond Dissociation

Energy

1. e- in Atom A are ATRRACTED nucleus in Atom B

2. e- in Atom B are ATRRACTED to nucleus in Atom A

3. e- in Atoms A and B REPULSE each other

4. Nuclei (+) in Atom s A and B REPULSE each other Atom A Atom B

+

-

-

-

Types of Bonds

CHEMICAL

• Within a compound

• Stronger

INTERMOLECULAR

• Between compounds

• Weaker

• van der Waals

• dipole

• hydrogen bonds

1. Covalent Bond:

• 2 Non-metal atoms share

some electron(s); ~equally

• molecule

• Bond drawn as line; C-H

• Orbitals overlap

1. Covalent

H

H

H

H C

Types of Bonds

CHEMICAL


• Stronger

Types of Bonds

CHEMICAL


• Stronger

1. Covalent

2. Polar covalent

2. Polar Covalent Bond:

• 2 Non-metal atoms share

some electron(s); unequally

• Partial charges ( +, -)

• Molecule

• Bond drawn as line; O-H

• Orbitals overlap

+

+

-

3. Ionic Bonds:

• results from the attraction of a

positive ion to a negative ion

• Often a metal (cation) to

non-metal (anion).

• A compound

• No orbital overlap

1. Covalent

2. Polar covalent

3. Ionic

Types of Bonds

CHEMICAL


• Stronger

Na+ Cl-

Types of Bonds

CHEMICAL


• Stronger

1. Covalent

2. Polar covalent

3. Ionic

4. Metallic

4. Metallic Bonds:

• Pure metals

• Valence electrons are not

strongly held by atoms nucleus.

• Delocalized valence electrons

• Sea of electrons around an array

of the positively charged core of

atoms

+

+

+

+

+ +

- -

-

- - -

- -

- -

-

-

-

H

H O

H

H

H

H C

covalent polar covalent ionic

A B

Electrons spend EQUAL

time around A and B

A B

Electron spend MORE

time around A than B

A B - +

Types of Bonds

How well do the share electrons?

Sharing means time!

Electron spend ALL

the time around A

covalent polar ionic

sharing

Electronegativity Electronegativity (EN): The capacity of an atom

in a molecule to attract shared electrons from

another atom

Difficult to actually measure

dec

rease

increase

Artificial scales are used to give relative strengths

This scale goes from 0.8 to 4.0

Electronegativity

Bond type between 2 atoms (AB):

1. Get the electronegativity for both atoms

2. Subtract the smaller value from the larger one

3. Compare result of subtraction to the bond scale.

1 2 3 0 0.4

ionic covalent polar

Electronegativity





1 2 3 0 0.4






Electronegativity

Determine the bond type for:

C-H

2.5 2.1 2.5 2.1 - = 0.4

D EN

1 2 3 0 0.4






Electronegativity

1 2 3


0 0.4


Na Cl

0.9 3.0 3.0 0.9 - = 2.1

D EN

Electronegativity Bond type between 2 atoms (AB):



3. Compare result of subtraction to bond scale.

1 2 3 0 0.4


O-H

3.5 2.1 3.5 2.1 - = 1.4

D EN


Bonding Topics in other Lectures

Valence electrons : Covalent Bonding

Simple dot structures

Topic: Lecture

Formula Unit: Ionic Bonding

Lattice

Compound & : Naming Compounds

Polyatomic naming

RECAP

• A bond is the joining of two or more atoms or ions under a

force of attraction

• When atoms or ions join they are considered a compound

• Bond formation is Favorable when energy is released upon

bonding

• The energy for breaking a bond is called the bond dissociation

energy

• Bond formation is Unfavorable when energy is consumed upon

bonding

• Bonding (A-B) is driven by the net sum of 4 forces:

1. e- in Atom A are ATRRACTED nucleus in Atom B

2. e- in Atom B are ATRRACTED to nucleus in Atom A

3. e- in Atoms A and B REPULSE each other

4. Nuclei (+) in Atoms A and B REPULSE each other

RECAP

• When the distance between nuclei is plotted against energy:

– The minimum energy is where the net attraction is at its maximum.

• The energy required to break the bond: bond dissociation energy

– The distance between nuclei, at the minimum energy, is the bond length

• There are 4 types of chemical bonding covered in this lecture:

1.Covalent

• atoms share some electron(s) ~equally; molecule

2.Polar covalent

•atoms share some electron(s) ~unequally; molecule; ( +, -)

3.Ionic

• results from the attraction of a cation to an anion; compound

4. Metallic

• Sea of e- around an array of the positively charged core of atoms

• The difference in electronegativity between 2 atoms determines

their bond type

– 0-0.4 covalent; 0.5-1.9 polar covalent; >2 ionic

Go check out the Covalent

Bonds and Ionic Bonds

lectures!

bonding: an overview€¦ · atom a atom b bonding: underlying forces distance between nuclei y net...

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