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