1. Chemical Bonding and Molecular Geometry
Honors Chemistry
Mr. Kinton
Enloe High School

2. Chemical Bonds
A strong attachment between 2 atoms or ions that is caused by the movement of electrons
Chemical bonds are considered intra-particle forces
How the 2 atoms or ions interact with one another
There are three different bond types that are significant to chemists

3. Chemical Bonds
Ionic Bond: electrostatic force of attraction that exists between ions of opposite charge
Formed from atoms by the transfer of one or more electrons from one atom to another
Covalent bond: electrostatic force of attraction between positive nuclei and negatively charged electrons
Formed by atoms sharing 2 or more electrons
Metallic Bond: electrostatic force of attraction between 2 metals
Formed by positively charged metal atoms interacting with delocalized outer electrons.

4. Ionic Bond Typically composed of a metal and a non-metal
More important a cation and an anion
All ionic compounds are solids at room temperature (25o C) with high melting points
All ionic compounds have high boiling points
Ionic compounds form brittle solids, are not malleable and not ductile
Aqueous and molten ionic compounds conduct electricty

6. Covalent Bonds
Can exist as solids, liquids, or gases at room temperature
Covalent molecules have a wide range of melting points
Most covalent molecules have a low boiling point
Some covalent molecules form brittle solids
Typically they are not malleable or ductile
Molecules that are small and have a low mass (MW ≤ 100 amu) will be gases at room temperature

8. Covalent Network Solids
Type of solid that has a 3-D structure that is held together by covalent bonds
All are solids at room temperature
Quartz (SiO2), diamond (C), and graphite (C)
Some form extremely hard solids
Can be malleable or ductile

10. Metallic Bond
All metals except mercury (Hg), are solids at room temperature
Most metals have extremely high boiling points
Form hard solids that do not break easily
Are malleable and ductile
None of the metals exist as gases at room temperature
Are conductors of electricity due to moving electrons
Metals have luster (shiny)
Malleability, ductility, luster, and electrical conductivity are all due to the free moving electrons

12. Identifying Bond Types
Determine the type of bond in each of the following pairs:
Na and F
Cu and O
H and F
Si and Cl
Ag and Ag
Cu and Ni

13. Lewis Dot Diagrams
A tool used to show the valence electrons for an element
For each valance electron an element has, a dot is placed around the element symbol
1 dot is placed around each side before pairing electrons
A maximum of 8 dots is allowed around an atom
Octet rule: states that bonded atoms tend to have 8 valence electrons

14. Lewis Dot Diagrams
Allow us to predict how many covalent bonds an atom is likely to form
7A elements like to form 1 covalent bond
6A elements like to form 2 covalent bonds
5A elements like to form 3 covalent bonds
4A elements like to form 4 covalent bonds
Hydrogen and Fluorine will always form 1 covalent bond and will be terminal

15. Lewis Dot Diagrams
Give the Lewis Dot diagram for each of the following: Se Cl Al C

16. Lewis Dot Diagrams, Lewis Structures and Covalent Bonds
From the Lewis Dot diagrams of 2 nonmetals a structure can be created to show how they are bonded together
Lewis Structure: representation of covalent bonding in a molecule using Lewis symbols.
Shared electrons are represented using lines connecting the 2 atoms
Unshared/lone pairs/nonbonding electrons are shown as pairs of dots around the atom
Only shows the valence electrons

17. Covalent Bonds and Lewis Structures
Bond Type
Single
Double
Triple
# of e- 2 4 6
Notation
Bond Order 1 3
Bond Energy
Increases from single to triple
Bond Length
Decreases from single to triple

18. Covalent Bond Terminology
Bond order: The difference between the number of bonding electron pairs and the antibonding electron pairs
Bond energy/enthalpy: the energy required to break a bond when the substance is in the gas phase
Bond length: distance between the centers of 2 bonded atoms

19. How to Draw Lewis Structures for Covalent Compounds
Method 1:
Find the total number of valence shell electrons (vse) from all atoms
Write the symbols for the atoms to show which atoms are attached to which and connect each atom with a single bond
When a central atom has a group of other atoms bonded to it, the central atom is usually written first in the chemical formula
In oxyacids, the hydrogen is always bonded to an oxygen. The other atom is the central atom
In some chemical formulas are written in the order the atoms are connected
Hydrocarbons always have the carbon atoms attached to each other

20. Method 1
Complete the octets of the atoms bonded to the central atom first
Hydrogen only needs 2 electrons
Boron only needs 6 electrons
Place leftover electrons onto the central atom
If the central atom does not have an octet, form double and triple bonds using the appropriate atoms

21. Drawing Lewis Structures for Covalent Compounds
Method 2
Count up the number of electrons needed to satisfy the octet rule (Need)
Count up the number of electrons available to satisfy the octet rule (Available)
Determine the number of electrons that are shared by taking the difference between what you Need and what is Available (S = N – A) (Shared). Then take S and divide by 2
Determine the difference between available and shared electrons (L = A – S) (Left Over). Then take L and divide by 2 to get the number of lone pairs on your structure

22. Lewis Structures
Draw the Lewis Structures for the following molecules: H2 O2
C2H6
BH3
HCN
HClO
NH4+

23. Lewis Structures for Ionic Compounds
Write as many of each element symbol as indicated in the chemical formula. Include their most likely charge
Draw the Lewis Dot diagram for each element. Use “x” for the electrons around the anion
Show the transfer of electrons from the cation to the anion using arrows

24. Lewis Structures for Ionic Compounds
Write the final Lewis structure for the compound
Use coefficients to indicate the number of each ion needed
Place brackets around the anion with the charge inside the brackets
Represent transferred electrons as dots and electrons present before transfer as “x”
No electrons should be represented for the cation.

25. Lewis Structures
Draw the Lewis Structure for the following ionic compounds:
LiF
Na2O
Al2O3

26. Valence Shell Electron Pair Repulsion
We know that like charges repel each other
A similar thing happens when our atoms form bonds
The electrons will repel each other if they get to close
As a result our Lewis structures are rough estimates about how our molecules are arranged
VSEPR: model that accounts for the geometric arrangements of shared and unshared electrons around a central atom in terms of the repulsions between the electrons

27. VSEPR Vocabulary
Bonding Domain: A location where electrons are being shared between 2 atoms
Double and triple bonds count as only 1 bonding domain
Nonbonding Domain: Location around the central atom where lone pairs/nonbonding electrons are located
Electron Domain Geometry: 3-D arrangement of the electron domains around an atom according to VSEPR
Molecular Geometry: The arrangement in space of atoms in a molecule

28. VSEPR
To use VSEPR appropriately we must first count the total number of electron domains
This is the sum of the bonding and nonbonding domains around the central atom
Then based on the number of domains we try to arrange the atoms attached to the central atoms as far apart from each other
Chemists also look at the bond angles to maximize the distance between the atoms
VSEPR alone will tell us the electron domain geometry

30. VSEPR and Lewis Structures
As you can see, the VSEPR model gives us a 3-D structure however a Lewis Structure only gives us a 2-D representation.
To help correct that we can draw Lewis Structures using wedge-dash notation to help represent the 3-D features of our molecule
A wedge represents an atom coming out towards you
A dash represents an atom going in away from you

32. Molecular Geometry and bond Angles
For linear molecules the bond angles do not change
For trigonal planar molecules, the bond angle will change from 120o to less than 120o for bent structures
For tetrahedral molecules, 2 changes can take place:
If one lone pair is present, the bond angles are approximately o
If 2 lone pairs are present, the bond angles are approximately o

33. VSEPR and Real Molecules
VSEPR does a great job of producing general structures
Sometimes what is predicted is not always what is observed
This is because lone pairs of electrons on the central atom take up additional space and alter the shape of the molecule
This also alters the bond angles around the molecule
The real molecule will sometimes have a different Molecular geometry than what VSPER predicts

34. VSEPR
Identify the electron domain geometry, molecular geometry and bond angles in the following molecules: H2 O2
BH3
HClO
HCN
C2H6
NH3

35. Bond Polarity
A measure of how equally the electrons are shared between 2 atoms in a chemical bond
Ionic bond: complete transfer of electrons from one atom to another
Covalent bond: sharing of electrons between atoms
Nonpolar covalent: equal sharing of electrons in a bond
Polar covalent: unequal sharing of electrons in a bond
This is due to differences in electronegativity

36. Bond Polarity Location on the Periodic Table
Electronegativity Difference
Difference
Bond Type
Nonpolar
0-1.7
Polar
1.8 or greater
Ionic
Look at the atoms that are bonded to each other:
If 2 of the same nonmetals are bonded, it will be nonpolar
If 2 different nonmetals are bonded, it will be polar
If a metal and a nonmetal are bonded, it will be ionic

37. Molecule Polarity A molecule that possesses a nonzero dipole moment
The molecule has a positive and negative end (2 poles)
Dipole: when 2 electrical charges of equal magnitude but opposite sign are separated by a distance
Dipole moment: a quantitative measure of the separation between the positive and negative charges
This helps us determine and explain properties that we observe at a macroscopic level, in lab, and in life

38. Molecule Polarity
To have a dipole moment the molecule most contain polar bonds and/or have lone pairs around the central atom
As a result, polar molecules have separate centers of positive and negative charge

39. Molecular Polarity
Polar Molecule
Nonpolar Molecule

40. How to Determine Molecular Polarity
Symmetrical molecules with no lone pairs around the central atom and all the atoms around the central atom are the same will be nonpolar
Any tetrahedral, trigonal planar, or linear molecule satisfying these conditions will be nonpolar
Any molecule that has one or more lone pairs around the central atom will be polar

41. Molecular Polarity
For each of the following molecules determine if they are polar or nonpolar: H2 O3
HCN
HClO
C2H6
BH3
NH3