Chapter 8 Chemical Bonding. Section 1: Types of Chemical Bonds Elements typically exist as compounds in nature. They are not often found alone. Type of bonding influences chemical and physical properties. Example: graphite and diamond.
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Elements typically exist as compounds in nature.
They are not often found alone.
Type of bonding influences chemical and physical properties.
Example: graphite and diamond.
Are silicon dioxide and carbon dioxide similar or different? Why?
Bond energy - The energy required to break a bond
allows us to obtain information about the strength of a bonding interaction
How do we know that a solution of sodium chloride actually consists of sodium ions and chloride ions?
It conducts electricity
This indicates to us that electrons are transferred from one substance to another.
Ionic Bonding- when bonding forces occur due to the attraction between oppositely charged ions
gives the energy of interaction between a pair of ions
Is it possible for a molecule to have polar bonds but not have a dipole moment?
p. 387 # 114
Examples: NaCl, CaO
What are some of the exceptions to the rule that ions form noble gas configurations?
Practice: p. 383-384 #’s 45 - 52
Represents the bonds of elements in the gaseous state and do not necessarily apply to the solid state.
Why is the existence of ions favored by the solid state? Many ions can interact and stabilize each other.
What is the “official” definition of ionic compounds?
Any compound that conducts an electric current when melted.
% ionic character = measured dipole moment of X—Y / calculated dipole moment of X+Y-
Why is it useful to think of a protein as a group of C—C, C—H, C—N, C—O, and N—H bonds?
This makes the molecules more understandable. We expect certain bonds to behave in certain ways
What is the delocalization of electrons?
The ability of electrons to move through the entire molecule- one of the flaws of the bond model
See page 350 for information on models
approximate energies for reactions
To break bonds, what must happen?
energy must be added to the system
endothermic- energy has + sign
To form bonds, what must happen?
energy is released
exothermic- energy has – sign
∆H = ∑D(bonds broken) - ∑D(bonds formed)
Energy of reaction = energy required to break bonds – energy required to form bonds
D always has a positive sign and is bond energy PER MOLE
Summarize any rules about Lewis Structures that you have not previously included:
When writing Lewis structures, satisfy the octet rule 1st and if electrons remain after the octet rule has been satisfied, place them on elements having available d orbitals
How do you determine where extra electrons go when it is not immediately clear?
assume extra electrons should be placed on the central atom
Formal charge = number of valence electrons on free atom – number of valence electrons assigned to the atom in the molecule
Valence electrons assigned = number of lone pair electrons + ½ number of shared electrons