Bond … Chemical Bond

What is Chemical Bonding???

A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together

ok, so…

it’s the attraction due to charges (+ and -)

Forces that link atoms together

Involves the valence electrons

So why do atoms bond?

TO BECOME MORE STABLE!!!!

Which electrons are involved in bonding?

It’s the VALANCE ELECTRONS

The outer most electrons

Maybe they’re shared,

Maybe they’re lost or gained

These are the electrons you have to worry about!!!

Types of Chemical Bonds

1. Covalent Bond

2. Ionic Bond

3. Metallic Bond

And…

James Bond

What Rule Is It?

Why is Ne, Ar, Kr, Xe, Rn so stable?

Complete outer shell

How many e- in the outermost shell

8

Bonding results because atoms want to be stable ~ they want to have a complete outer shell

And the rule is…

Octet Rule

chemical cmpds tend to form so that each atom, by gaining, losing or sharing e-, has an octet of e- in its highest E-level

aka – YOU WANT 8 IN THE OUTER SHELL

Don’t Write This!

There are some exceptions to the octet rule, however we will cover these when we get into writing Lewis Dot Structures.

1. Covalent Bonding

The SHARING of electron pairs

Valance electrons

Bond between 2 or more non-metals resulting in a molecule

Properties: low melting and boiling points, do not conduct electricity, typically liquids or gases.

C.B. – EX: Br + F BrF

Neither F nor Br easily lose e-

They get drawn together until their outer shells overlap

They now share their

valance e-

Br FBr

F+

Now each atom has a complete valance shell of 8 e-

C.B. – EX: H2 + O H2O

H and O can both pick up e-

How many does H need? O need?

1 e- 2 e-

O

H

H

+H

H

O

Multiple Bonds (double + triple)

The past two examples showed a single covalent bond.

This is not the only type

There are also double bonds and triple bonds

How many e- are shared in a double? In a triple?

O2 and N2

O2 and N2 are gases that contain multiple bonds. One pair of electrons is shared in each bond.

O2 N2

Now at any given time each atom has a complete valance shell, the octet rule is followed

OO NN

Lewis Diagrams

Lewis and Langmuir

developed a way to

represent molecules

Pairs of dots used

to represent valence

electron pairs

Irving Langmuir was the first to Irving Langmuir was the first to use the term “Covalent” use the term “Covalent”

Lewis Dot Structures

Step 1: The element symbol represents the nucleus and all e- except valence.

Step 2: Determine the # of valence electrons. These e- are the ones with the largest principal quantum numbers in the electron configurations.

Quick practice

Determine the nbr. of Valance e-

Li Be B C N O F Ne

Where are each of these elements located on the P.T. (pat attention to their group)

1 2 3 4 5 6 7 8

Remember what is the max. nbr. of valance e- that an atom can hold?

Octet Rule

Lewis Dot Structures

EX: carbon

step 1: C

step 2: 4 valance e-

step 3: C

>One more note: when filling the orbitalsaround the symbol there are an “s” and (3) “p”>So you fill them just like filling e- config.

s

pz px

py

Lewis Dot Structures

EX: bromine

step 1: Br

step 2: 7 valance e-

step 3: Br

Draw Lewis Dot Diagrams for…Phosphorus P

Chlorine Cl

Cesium Cs

Selenium Se

Silicon Si

Calcium Ca

Lewis Structures for molecules

1. Determine the total number of valence electrons in the molecule.

SF2

Total = 20 Valence e-

2. Arrange atoms to form a skeleton structure. Atom that needs the most e- to complete their octet goes in the center.

F S F

Lewis structures cont.

3. Use pairs of electrons (dots) to bond atoms. Put (2) dots in between each element, this represents a single bond.

F S F

Lewis structures cont.

4. Use remaining valence e- to give each atom an octet or full valence shell.

F S F

Since Chemists are lazy we take the e- that are shared and exchange them for solid lines (bonds)

1 line = pair of e-

F S FYou’re Finished!!

Exceptions

Now that you’ve mastered the Lewis dot diagrams and the octet rule you should know that there are exceptions to the octet rule

They involve the atoms of H, B, etc.

Exceptions

1. If you have extra e- and all of the atoms have an octet, put the extra e- on the central atom in pairs. (If the central atom has an atomic number greater than fifteen, you are allowed to have more than eight e- around it).

2. Boron tends to be stable with only 6 e- (rather than 8) in some compounds. Ex. BF3

3. Hydrogen does not follow the octet rule, instead it follows the duet rule, it only needs 2 e- to satisfy its outer energy level

More examples

HBr

H2S

CF4

O2

CO2

Try the following examples…

HF

CH4

SiF4

C2H4

C2H6

A little trick, that almost always works

If you didn’t already notice certain atoms like to form specific bonds, for example…

Carbon (and family) – likes to be a central atom and form 4 bonds

Nitrogen (and family) – likes to form 3 bonds

Oxygen (and family) – likes to form 2 bonds

Halogens – like to form 1 bond

Ions

These are very simple

How do you form a cation Loose an electron This mean you will subtract an e-

How do you form a anion Gain an electron This means you will add an e-

Lets try some

How many e- in NO3-

24

How many e- in PO33-

26

How many e- in NH4+

8

How to draw them…

Draw them just like a Lewis structure

Add in brackets and the charge

Practice

NH4+

ClO-

CN-

SiO32-

AsO33-

2. Ionic Bonding

Transfer of an e- from a metal to a nonmetal resulting in oppositely charged ions

Atoms lose an e- and become a…

Cation

Atoms gain an e- and become a…

Anion

Prop. of ionic cmpds: brittle, crystalline solids, good conductors of electricity when molten or dissolved in water, high melting and boiling points.

Electron transferred from one atom to the other

Oppositely charged ions attract

EX: Na+ + Cl- NaCl

Lewis Dot Structures for Ionic Bonds

Draw Lewis dots for each element.

Na + Cl

Draw an arrow to show the e- exchange between atoms.

Now draw them together.

[Na]+[ Cl ]-

Ionic bonds form because of the attraction between the pos. and neg. charges.

What Type of Bond???

How can you tell what bond will form

IndicatorsMetal and nonmetal will form a ionicUsually (2)+ nonmetals will form a covalent

However the one determining factor is that of Electronegativity

Covalent can either be polar or non-polar

Before we talk about EN, what is this polar/non-polar thing?

A molec. can have an overall charge

We can use EN to tell if a covalent bond is either polar or non-polar

We can also figure out in which part of the molec. is pos. and which part is neg.

Remember that electronegativity is the ability of an atom to attract an e- when bonded to another atom.

Bond Type – told by diff. in EN

>1.7 = IONIC

<0.3 = NON-POLAR COVALENT

I

N

C

E

N

0.3-1.7 = POLAR COVALENT

Bond Type

M – O |3.50 – 1.23| = 2.27 IONIC

B – P |2.01 – 2.06| = 0.05 NON-POLAR COVALENT

Mg – N |1.23 – 3.07| = 1.84 IONIC

C – Na |2.50 – 1.01| =1.49 POLAR COVALENT

3. Metallic Bond

Metals bonding with other metals DO NOT gain, lose e- or share e-.

Bonds are created from the delocalized e- that hold metallic atoms together.

Electrons flow like “a sea of charge”.

Properties: good conductors of electricity and heat, malleable and ductile, “shiny” reflective appearance

4. James Bond