# Part 1:Lewis Dot Diagrams and Structures

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Part 1:Lewis Dot Diagrams and Structures
Lesson 4 – Lewis Diagrams and Molecular Geometry Part 1:Lewis Dot Diagrams and Structures

Review of Chemical Bonds
There are 3 forms of bonding: _________—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) forming oppositely charged ions that attract one another _________—some valence electrons shared between atoms _________ – holds atoms of a metal together

The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together.

Electronegativity Difference
If the difference in electronegativities is between: ≥ 2.0: Ionic 0.>0.4 to < 2.0: Polar Covalent 0.0 to 0.4: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

Review of Valence Electrons
Remember from the electron arrangement that valence electrons are the electrons in the OUTERMOST energy level. B is 1s2 2s2 2p1; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons! Br is [Ar] 4s2 3d10 4p5 How many valence electrons are present?

Lewis Dot Diagrams A way of keeping track of valence electrons in ionic compounds. How to write them? Write the symbol. Put one dot for each valence electron Don’t pair up until they have to (Hund’s rule) X

The Lewis Dot diagram for Nitrogen
Nitrogen has 5 valence electrons. First we write the symbol. N Then add 1 electron at a time to each side. Until they are forced to pair up.

Ca Lewis Dots For Cations
Metals will have few valence electrons (usually 3 or less) Ca

Ca Lewis Dots For Cations Metals will have few valence electrons
These will come off Ca

Ca2+ Lewis Dots For Cations Pseudo-noble gas configuration
Metals will have few valence electrons These will come off Forming positive ions Ca2+ Pseudo-noble gas configuration

P P3- Lewis Dots For Anions
Nonmetals will have many valence electrons (usually 5 or more) They will gain electrons to fill outer shell. P P3-

Ionic Bonding Anions and cations are held together by opposite charges. The bond is formed through the transfer of electrons. Electrons are transferred to achieve noble gas configuration (octet rule).

Lewis Dot Diagrams Ionic Bonding
Na Cl

Lewis Dot Diagrams Ionic Bonding
Na+ Cl-

Lewis Dot Diagrams Ionic Bonding
All the electrons must be accounted for! Ca P

Lewis Dot Diagrams-Ionic Bonding
Ca P

Lewis Dot Diagrams Ionic Bonding
Ca2+ P

Lewis Dot Diagrams Ionic Bonding
Ca2+ P Ca

Lewis Dot Diagrams Ionic Bonding
Ca2+ P 3- Ca

Lewis Dot Diagrams Ionic Bonding
Ca2+ P 3- Ca P

Lewis Dot Diagrams Ionic Bonding
Ca2+ P 3- Ca2+ P

Lewis Dot Diagrams Ionic Bonding
Ca Ca2+ P 3- Ca2+ P

Lewis Dot Diagram Ionic Bonding
Ca Ca2+ P 3- Ca2+ P

Ionic Bonding Ca2+ Ca2+ P 3- Ca2+ P 3-

Lewis Dot Diagram Ionic Bonding
= Ca3P2 Formula Unit

Lewis Structures –Covalent Bonding

Covalent bonds Nonmetals hold on to their valence electrons.
Still want noble gas configuration. By sharing, both atoms get to count the electrons toward a noble gas configuration.

Covalent bonding Fluorine has seven valence electrons F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… …both end with full orbitals F F

F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven By sharing electrons… …both end with full orbitals F F 8 Valence electrons

Drawing Lewis Structures
Find total # of valence e-. Arrange atoms - singular atom is usually in the middle. Form bonds between atoms (2 e-). Distribute remaining e- to give each atom an octet If there aren’t enough e- to go around, form double or triple bonds.

H O Water Each hydrogen has 1 valence Electron (Total of 2e)
Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy H O

H O Water Put the pieces together (8 e to distribute).
The first hydrogen is happy The oxygen still wants one more H O

H O H Water The second hydrogen attaches
Every atom has full energy levels Remember to check count. H O H

Drawing Lewis Structures
CF4 1 C × 4e- = 4e- 4 F × 7e- = 28e- 32e- F F C F - 8e- 24e-

Drawing Lewis Structures
BeCl2 1 Be × 2e- = 2e- 2 Cl × 7e- = 14e- 16e- Cl Be Cl - 4e- 12e-

Multiple Bonds Sometimes atoms share more than one pair of valence electrons. A double bond is when atoms share two pairs (4 total) of electrons A triple bond is when atoms share three pairs (6 total) of electrons Know which elements are diatomic (Oxygen?)

C O Carbon dioxide CO2 - Carbon is central atom ( more metallic )
Carbon has 4 valence electrons Oxygen has 6 valence electrons (total of 12e) 16e must be distributed. C O

Carbon dioxide Attaching 1 oxygen leaves the oxygen 1 short, and the carbon 3 short C O

Carbon dioxide Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short IF the central atom is not surrounded by 4 electron pairs, it does not have an octet. You must convert one or more of the lone pairs on the terminal atoms to a double or triple bonds. O C O

Carbon dioxide The only solution is to share more O C O

Carbon dioxide The only solution is to share more O C O

Carbon dioxide The only solution is to share more O C O

Carbon dioxide The only solution is to share more O C O

Carbon dioxide The only solution is to share more O C O

Carbon dioxide The only solution is to share more O C O

O C O Carbon dioxide The only solution is to share more
Requires two double bonds Each atom can count all the electrons in the bond O C O

O C O Carbon dioxide 8 valence electrons
The only solution is to share more Requires two double bonds Each atom can count all the electrons in the bond Count e’s 8 valence electrons O C O

O C O Carbon dioxide The only solution is to share more
Requires two double bonds Each atom can count all the electrons in the bond 8 valence electrons O C O